WO2017019577A1 - Catalyseur, procédé et système pour l'oxydation sélective de monoxyde de carbone - Google Patents

Catalyseur, procédé et système pour l'oxydation sélective de monoxyde de carbone Download PDF

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WO2017019577A1
WO2017019577A1 PCT/US2016/043783 US2016043783W WO2017019577A1 WO 2017019577 A1 WO2017019577 A1 WO 2017019577A1 US 2016043783 W US2016043783 W US 2016043783W WO 2017019577 A1 WO2017019577 A1 WO 2017019577A1
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catalyst
water
particles
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gas
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Bert D. CHANDLER
Johnny SAAVEDRA
Christopher J. PURSELL
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen; Reversible storage of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification
    • C01B3/56—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
    • C01B3/58—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction
    • C01B3/583—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction the reaction being the selective oxidation of carbon monoxide
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    • B01J2208/00168—Controlling the temperature by indirect heat exchange with heat exchange elements outside the bed of solid particles
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    • B01J2235/15—X-ray diffraction
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P20/584—Recycling of catalysts

Definitions

  • the filed of the invention relates to purification of gases by CO oxidation, and catalysts and systems therefor.
  • the primary production method of hydrogen gas as an industrial feedstock is via steam reforming, wherein a mixture of methane and other light hydrocarbons is reacted with water at high temperature in the presence of a metal catalyst to produce H 2 and C0 2 according to reaction formula 1, shown below.
  • CO is also a common contaminant in other gas feedstocks, particularly those produced through partial oxidation chemistries.
  • CO is a well-known poison for many industrial reactions, and as such must be removed from the gas prior to downstream processing.
  • many catalytic processes are highly sensitive to CO. The CO strongly binds to the catalyst in place of the desired substrate resulting in partial or total deactivation of the reaction.
  • Some processes that require CO-purified gaseous feedstocks include: H2/N2 streams used in ammonia synthesis (Haber-Bosch Process)- 140 million tones NH3 produced/year
  • adsorption separations require operating the process at high pressure (typically between 5 and 10 atm) to achieve high removal efficiencies.
  • High pressure results in the physical attrition of the sorbent particles, which diminishes their adsorption capacity and necessitates the inclusion of additional beds in the process.
  • PSA is a capital-intensive process and has low volume throughput, making it cost effective only in low volume, specialty gas separations. Further, PSA is a relatively slow process, which reduces hydrogen throughput and requires substantially higher capital expenditures for multiple large separation units.
  • Separation membranes have also been adapted to eliminate CO.
  • the most viable membranes allow only one small chemical species, such as hydrogen through the membrane while all the other reformate gases are retained.
  • Membranes are constructed of either inorganic ceramics or precious metal alloys of Pd. In comparison to PSA, these systems typically operate with 40 - 50 psi differential pressure at temperatures up to about 200 °C making them inefficient and/or expensive. Scrubbers employ liquid - gas interactions to remove the contaminants. While proper selection of stripping agent allows these processes to be very selective, they are complicated systems that use specialty chemicals. Additionally, the units require multiple steps to transfer the contaminant from gas phase to liquid, then from liquid back to gas phase, which is ultimately vented. Scaled up processes have found limited applications in the hydrogen purification industry.
  • Methanation is commonly used to remove CO from the hydrogen feed in ammonia synthesis (e.g. the Haber-Bosch process).
  • methanation requires relatively high temperatures (300° C) to be efficient and is unselective for CO, resulting in substantial reaction between hydrogen and the C0 2 that is also typically present in the feed.
  • methanation consumes a substantial portion of the hydrogen that has been produced via the steam reforming and WGS reactions. The combination of all these factors typically results in loss of 3- 10% of the produced hydrogen and requires this secondary methane to either be recycled or used as fuel for high temperature units. While methanation processes successfully remove CO, they result in substantial energy losses (nominally 5-15%) for the overall hydrogen production and purification process.
  • the ideal PROX catalyst must have high activity at low temperatures ( ⁇ 150 °C), preferably below 100 °C, and most preferably below 50 °C.
  • the catalyst must also be highly selective for CO oxidation over H 2 oxidation, with at least 50% of the consumed oxygen used to oxidize CO, preferably more than 70% of the consumed oxygen used to oxidize CO, and most preferably more than 85% of the consumed oxygen used to oxidize CO.
  • a reduction of the CO to below 10 ppm or below 1 ppm with high 0 2 selectivity (> 50%) will make CO PROX catalysts viable for the purification of H 2 for fuel cells, ammonia synthesis, and other processes where CO presents problems in downstream feeds.
  • the ability to operate over a wide temperature range is desirable as well.
  • having high PROX activity at temperatures near the operating temperature of the fuel cell (70-90 °C) is highly desirable.
  • the PROX catalyst may be required to operate at approximately 20-30 °C.
  • the ability to operate CO PROX over a wide range of temperatures, particularly temperatures close to the temperature required for either preceding or subsequent processing steps, may eliminate the necessity of cooling the gas streams and provide a substantial economic advantage.
  • CO PROX catalysts materials composed of mixed copper and cerium oxides have been examined as CO PROX catalysts; however, these materials are poisoned by CO2 and H2O, which are common impurities in the hydrogen and light hydrocarbon feeds. Carbon dioxide is also the reaction product and is therefore extremely difficult to remove as the reaction proceeds.
  • H2O/CO2 the CuOx/Ce20 3 catalysts must be operated in a very narrow temperature window. Achieving acceptable activity and selectivity in this temperature window remains a substantial technical challenge for these catalysts.
  • gold based PROX catalysts have exceptional CO oxidation activity (high reaction rates) at low temperatures ( ⁇ 100 °C) and have exceedingly poor hydrogenation activity relative to traditional noble metal catalysts. This makes Au the most promising catalyst for the CO PROX reaction.
  • Strategies to optimize Au catalysts used in CO PROX have included: adjusting metal particle size, incorporating heterometals in order to increase O2 activation activity, modifying the metal oxide identity used as support by the combination of metal oxides with the primary goal to increase the selectivity towards CO oxidation compared to H2 oxidation (using mixed/combined oxides), and varying the metal oxide morphology (porous/nanoscale metal oxides).
  • state of the art Au catalysts have not been able to consistently achieve the activity and selectivity necessary to achieve CO PROX performance adequate for industrial requirements.
  • Catalysts should desirably have sufficient activity and selectivity over a wide range of reaction conditions to compensate for various operating conditions and changes that occur during the catalyst and process lifetime.
  • a preferential CO oxidation reaction (PROX) catalyst comprising: a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm; a hydrophilic support in contact with the particles; and about 0.1 to about 10 monolayers of water on a surface of the support.
  • PROX preferential CO oxidation reaction
  • a preferential CO oxidation reaction (PROX) catalyst is provided, which is prepared by process comprising: removing one or more of an adsorbed carbonate, bicarbonate, carboxylate, organic carbonate, adsorbed hydrocarbon, or a mixture of two or more thereof from a surface of a supported catalyst, the supported catalyst comprising a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm and a hydrophilic support in contact with the particles; and simultaneously or thereafter adsorbing about 0.1 to about 10 monolayers of water on a surface of the support.
  • PROX preferential CO oxidation reaction
  • a method for preparing or regenerating a preferential CO oxidation reaction (PROX) catalyst comprising: removing one or more of adsorbed carbonate, bicarbonate, carboxylate, organic carbonate, adsorbed hydrocarbon, or a mixture of two or more thereof from a surface of a supported catalyst, the supported catalyst comprising a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm and a hydrophilic support in contact with the particles; and simultaneously or thereafter adsorbing about 0.1 to about 10 monolayers of water on a surface of the support.
  • PROX preferential CO oxidation reaction
  • a process for oxidizing CO comprising: contacting the catalyst and a feed gas comprising CO, 0 2 and H 2 0 at a temperature ranging from about 0 to about 300 °C, to thereby oxidize the CO.
  • a process for oxidizing CO comprising: contacting the catalyst and a feed gas comprising CO, O2 and H 2 0 at a temperature ranging from about 0 to about 300 °C, to thereby oxidize the CO and produce a first product gas comprising 1000 ppm or less of CO; optionally, adding or removing one or more of O2, H2O, or both to or from the first product gas, to optionally form a second feed gas; contacting the first product gas or second feed gas with a second catalyst at a temperature ranging from about 0 to about 300 °C, to thereby oxidize said CO.
  • a process for oxidizing CO comprising: contacting the catalyst and a feed gas comprising CO, O2 and H2O at a temperature ranging from about 0 to about 300 °C, to thereby oxidize the CO; wherein the catalyst is distributed along a catalyst bed having an upstream portion and a downstream portion, and wherein the temperature of the upstream portion is higher than the temperature of the downstream portion.
  • a treatment method for producing highly active Gold based catalysts to be used in the preferential CO oxidation reaction, improving the catalyst resistance to deactivation, and optimizing the use of catalytic metal by allowing for high gas throughput.
  • a technology based on a dual-step process for performing the CO oxidation reaction with increased activity (elevated throughput), more efficient use of the metal (high turnover rates), increased stability (resistance to deactivation over time), and increased selectivity (avoiding undesired side reactions, 3 ⁇ 4 oxidation, methanation, WGS, etc).
  • a process for the flexible operation of the preferential CO oxidation reaction, allowing for high performance under a wide variety of process operating conditions, including temperature, feed content of water and CO2.
  • a process is provided that allows for the purification of a wide variety of gases including, but not limited to, hydrocarbon streams (C1-C10 alkanes, alkenes, and functionalized hydrocarbons) and permanent gases (N 2 , 0 2 , H 2 , Air, He, Ar, etc).
  • a composition of Au nanoparticles for CO oxidation a process for synthesizing the same catalyst, and processes for using the same catalyst for purifying gas streams by converting CO to C0 2 .
  • catalysts and processes are provided that are capable of selectively oxidizing CO in the presence of other gases including H 2 , N 2 , methane, ethane, and others for the purification of said gas streams under a variety of conditions.
  • a compositionally controlled catalyst capable of removing carbon monoxide (CO) from gas mixture via oxidation of CO to carbon dioxide (C0 2 ) by using supported gold nanoparticle catalysts with specific ratios of water content in the reactive gas mixture and on the surface of the catalyst. Careful control over the amount of water adsorbed on the catalysts generates a new composition of matter that allows for high CO oxidation activity while limiting the oxidation of hydrogen, hydrocarbons, and other molecules. This can be suitably applied to the purification of non-condensable hydrocarbon streams (C1-C3 alkanes and alkenes) and permanent gases (N 2 , 0 2 , H 2 , Air, He, Ar, etc).
  • non-condensable hydrocarbon streams C1-C3 alkanes and alkenes
  • permanent gases N 2 , 0 2 , H 2 , Air, He, Ar, etc.
  • the resulting purified gases can be used in applications and processes that are sensitive to the amount of CO in the feed gas, such as fuel cells and processes employing metal catalysts.
  • This can also be used in the purification of hydrogen and light hydrocarbons and may be used as a replacement for methanation processes in hydrogen production and purification, particularly for ammonia synthesis, petroleum refining, and the production of high purity gases.
  • a compositionally controlled catalyst capable of removing carbon monoxide (CO) and oxygen (0 2 ) from gas mixture via oxidation of CO to carbon dioxide (C0 2 ) by using supported gold nanoparticle catalysts with specific ratios of water content in the reactive gas mixture and on the surface of the catalyst, followed by a secondary catalyst bed containing a hydrogenation or oxidation catalyst for reacting the remaining 0 2 with the feed gas (e.g. H 2 ).
  • This can be suitably applied to the purification of non-condensable hydrocarbon streams (C1-C3 alkanes and alkenes) and reactive permanent gases (0 2 , H 2 , Air, etc).
  • the resulting purified gases can be used in applications and processes that are sensitive to the amount of CO and 0 2 in the feed gas, such as fuel cells and processes employing metal catalysts.
  • This can also be used in the purification of hydrogen and light hydrocarbons and may be used as a replacement for methanation processes in hydrogen production and purification, particularly for ammonia synthesis, petroleum refining, and the production of high purity gases.
  • Fig 4. Effect of thermal treatments and carbonate deposition during CO oxidation on the water adsorption capacity of a Au/Ti0 2 catalyst.
  • the H 2 treatment involved heating under flowing H 2 (lOOmL/min, 250 °C, 16 h) ( «); regeneration refers to slowly cooling the catalyst immediately after the H 2 treatment under H 2 0/N 2 (4000 Pa H 2 0, 20 °C, 12 hr, 100 mL/min N 2 ) (®).
  • the "carbonated" catalyst was operated under CO oxidation conditions (1% CO, 20% 0 2 , 20 °C, 1 h, Dry gas) ( ⁇ ) and was again regenerated (o).
  • Fig 6. PROX performance and deactivation of AU/AI2O3 with water in the feed (1% CO, 1.4% O2, 60% H 2 , balance He).
  • A Performance comparison between AU/AI2O3 operated at 40 °C and 80 °C (various space velocities, 1-20 Torr H2O, see Fig. 7) and literature reports (Table 8). When feed water content and space velocity are properly controlled, this AU/AI2O3 catalyst far surpasses literature reports for CO PROX performance, easily achieving literature benchmarks.
  • B CO conversion and
  • C O2 selectivity during 10 hour experiments with AU/AI2O3 at 80 °C. When water is removed, selectivity immediately drops; CO oxidation activity also drops, but more slowly. Thus, maintaining sufficient water on the catalyst prevents deactivation over 10 hours, and is critical for optimum catalyst performance. CO conversion measurement errors are typically + 0.02%; O2 selectivity measurements are typically + 5%.
  • FIG. 7 PROX reactivity over AU/AI2O3 at high conversion.
  • Panel (A) shows CO slip versus PH2O at several space velocity values; CO slip ⁇ concentration of CO in the reactor outlet. At 40 °C, activity (low CO slip) and selectivity ( ⁇ 90%) are maximized at ⁇ 5 Torr added water; CO oxidation activity increased at 80°C, but the reaction was less sensitivity added water.
  • Panel (B) shows CO slip versus SV for the data in panel A;
  • panel (C) shows O2 selectivity versus SV for the data in panel (A). The data demonstrate controlling space velocity can tune catalyst performance. When the space velocity is low, very low CO slips ( ⁇ 5ppm) are achieved, but at the expense of O2 selectivity.
  • Fig. 8 Effect of SV on CO PROX catalysis over Au/Al 2 0 3 .
  • A CO conversion as a function of water content at several different values for the space velocity;
  • B 0 2 selectivity for C0 2 as a function of CO conversion at 20°C.
  • Fig. 9 Effect of water and temperature on CO PROX catalysis over Au/Al 2 0 3 .
  • A Normalized nominal activity
  • B 0 2 selectivity for C0 2 as a function of Pmo and temperature.
  • Activity measurement errors are typically + 0.02%; 0 2 selectivity measurement errors are + 5%.
  • FIG. 10 Gas adsorption data.
  • A Volumetric water adsorption isotherms (20-50 °C) on the Au/Al 2 0 3 catalyst. As the temperature increases, the amount of water adsorbed on the catalyst at a given pressure decreases substantially. The box indicates the range of ⁇ 2 ⁇ that corresponds to the activity maxima in Figure 9A and Table 1. There is a relatively narrow range of water coverage enabling the highest CO oxidation activity, regardless of the reaction temperature.
  • B CO adsorption isotherms (20°C) determined by infrared spectroscopy in the presence and absence of water. At pressures as low as 2.3 Torr, where total CO oxidation activity is maximized, roughly half of the CO adsorption sites are blocked by water.
  • Fig. 12 Changes in FTIR spectra showing D 2 0 treatment of AU/T1O2 and AU/AI2O3 (30 mg) wafers at 20°C. The top (blue) spectra were collected after H2O saturation; the bottom (red) spectra were collected after D2O interchange.
  • Fig. 13 Proposed reaction mechanism for CO oxidation over AU/T1O2 in the presence of water.
  • A Potential energy diagram; both pathways are limited by a combination of *COOH decomposition and the reaction between *CO and *0(H).
  • B Schematic representation of the lower (green) pathway (* indicates an adsorbed species).
  • KIE Kinetic Isotope Effect
  • Fig. 18 Effects of added water on CO oxidation in the presence (PROX) and absence (CO Oxidation) of H2 at 20 °C. Rates are normalized to the maximum observed conversion.
  • Fig. 19 Water adsorption isotherms for AU/AI2O3 at 20, 30, 40, and 50 °C.
  • Fig. 20 XPS data for the Au/Al 2 0 3 catalyst.
  • Fig 21 XRD data for the AU/AI2O3 catalyst.
  • Fig. 22 Effects feed water content on CO oxidation activity by Au/Ti0 2 and Au/Al 2 0 3 catalysts shown through plots of (A) Activity vs. Pmo (B) reaction order plots, and (C) reaction order based on the amount of weakly adsorbed water (wH 2 0). Reaction conditions: 1% CO, 20% 0 2 , 22 °C.
  • Fig. 23 Adsorption isotherms (A) and linear Langmuir plots (B) at 20 °C for weak water adsorption on Au/Al 2 0 3 and Au/Ti0 2 .
  • Fig. 24 Effects of added water on CO adsorption.
  • A Au-CO peak area, measured via infrared spectroscopy, as a function of water pressure.
  • B Au-CO peak area during drying with 1% CO/N 2 after saturating with water at several Pmo.
  • Fig. 25 Infrared spectra of H 2 0 and D 2 0 exchanged (A) Au/Ti0 2 and (B) Au/Al 2 0 3 .
  • Fig. 26 CO oxidation H(D) kinetic isotope effects experiments for Au/A1203.
  • A average KIE for 7 experiments with H 2 0 and D 2 0 exchanged treated samples.
  • B Effects of adding and removing 700 Pa H20/D20 to co Au/Al 2 0 3 catalytic activity. All testing was performed at (20 C with a 1% CO and 20 % 0 2 feed.
  • Fig. 27 Kinetic parameters for Au/Ti0 2 and Au/Al 2 0 3 catalysts.
  • Fig. 28 CO oxidation in presence of 600 ppm of H 2 0 on Au/Al 2 0 3 .
  • Fig. 30 Decrease in CO adsorption capacity on a Au/Ti0 2 catalyst due to the presence of H 2 0 in the gas.
  • the CO adsorption changes were monitored using the Au-CO integrated peak (-2100 cm "1 in the IR spectra). All spectra are referenced to the catalyst pellet (at 20°C) after drying at 120°C (N 2 ) for 1 hr.
  • Fig. 32 PROX catalysis showing CO slip and C0 2 selectivity as a function of water pressure for a Au/Al 2 0 3 catalyst operating at 50 °C.
  • Fig 33 PROX catalysis showing CO slip and C0 2 selectivity as a function of water pressure for a Au/Ti0 2 catalyst operating at 50 °C.
  • Fig. 34 Effects of heating protocol on Au/Al 2 0 3 catalyst performance.
  • Fig. 35 PROX catalysis showing CO slip and C0 2 selectivity as a function of water pressure for a Au/ZnO catalyst operating at 80 °C.
  • Fig. 36 PROX catalysis showing CO slip and CO2 selectivity as a function of water pressure for a Au/Si0 2 catalyst operating at 80 °C.
  • PROX results for single-stage, dual-bed catalyst arrangement for removing CO and 0 2 from a hydrogen stream.
  • the invention provides a preferential CO oxidation reaction (PROX) catalyst, comprising: a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm; a hydrophilic support in contact with the particles; and about 0.1 to about 10 monolayers of water on a surface of the support.
  • the active catalyst is composed of gold nanoparticles interacting with a hydrophilic support with a thin layer of water adsorbed on the support. This thin layer of water is critical to the operation of the catalyst, and has not been previously described or employed.
  • the gold nanoparticles can range in size from 0.5-20 nm, but preferably are smaller than 10 nm and most preferably smaller than 5 nm.
  • Numerous supports can be used, including metal oxides (such as alumina, titania, silica, ceria, ZnO, iron oxides, manganese oxides, etc.), mixed metal oxides, metal hydroxides, zeolites, clays, etc. with the key feature being that the support adsorbs and retains water under the reaction conditions.
  • the preferred support will vary based on the desired reaction conditions, with supports that bind water more strongly being preferred for higher temperature reactions and / or lower water content gas feeds and supports that bind water less strongly preferred for lower temperature reactions and / or higher water content gas feeds.
  • the layer of adsorbed water can range from 0.1 monolayer to multiple monolayers, and can be adjusted to help control catalytic activity.
  • the practical maximum height of the water layer is approximately 5 water monolayers higher than the height of the Au nanoparticles.
  • the hydrophilic nature of the support allows the water layer to be controlled by adjusting the amount of water in the reactive gas. Additional promoters such as alkaline or alkaline earth metals and metal hydroxides may also be added to the catalyst.
  • the Au or Ag particles have a size ranging from about 0.5 to about 15 nm. In some embodiments, the particles have a size ranging from about 0.5 to about 10 nm. In some embodiments, the particles have a size ranging from about 0.5 to about 5 nm. In some embodiments, the particles have a size ranging from about 0.5 nm to less than 5 nm.
  • the hydrophilic support is metal oxide, mixed metal oxide, metal hydroxide, zeolite, vermiculite, clay, silica-alumina, mixed manganese oxide, Mn0 2 , A1 2 0 3 , CeioAlOx, Ce 2 A10x, Ce-Al-O x , Ce-Co-O, Ce-Cu-O x , CeFeOx, Ce-Fe-O x , Ce-Mn-O x , Ce0 2 , Ce0 2 nanocrystal, Ce0 2 nanocube, Ce0 2 nanorod, Ce0 2 polyhedra, Ce0 2 /Ti0 2 , Ce0 2 -Co 2 0 3 , Ce0 2 - Fe 2 0 , CeZnOx, CeZrOx, Fe 2 0 , Fe-Ce-O x , Mn-Ce-O x , Mn0 2 -Ce0 2 , MnO x -Ce0 2 , Mn
  • the hydrophilic support is A1 2 0 3 .
  • the support further comprises a promoter.
  • the promoter is selected from the group consisting of alkaline metal, alkaline earth metal, alkaline metal hydroxide, alkaline earth metal hydroxide, and a mixture of two or more thereof.
  • the surface comprises an intersection of the support and one or more of the particles.
  • the layer of adsorbed water comprises about 0.1 to about 5 monolayers of water on the surface of the support. In some embodiments, the layer of adsorbed water comprises about 0.1 to about 2.5 monolayers of water on the surface of the support. In some embodiments, the layer of adsorbed water comprises about 0.5 to about 2.5 monolayers of water on the surface of the support. In some embodiments, the layer of adsorbed water comprises about 1 to about 2 monolayers of water on the surface of the support.
  • less than about 50% of the surface comprises a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate. In some embodiments, less than about 25% of the surface comprises a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate. In some embodiments, less than about 10% of the surface comprises a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate. In some embodiments, less than about 5% of the surface comprises a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate. In some embodiments, less than about 1% of the surface comprises a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate. In some embodiments, the surface does not comprise a surface bound carbonate, bicarbonate, carboxylate, or organic carbonate.
  • the particles are present in an amount ranging from about 0.1 to about 60% by weight of the catalyst. In some embodiments, the particles are present in an amount ranging from about 0.1 to about 30% by weight of the catalyst. In some embodiments, the particles are present in an amount ranging from about 0.1 to about 10% by weight of the catalyst. In some embodiments, the particles are present in an amount ranging from about 0.5 to about 10% by weight of the catalyst.
  • the preferential CO oxidation reaction (PROX) catalyst is prepared by process comprising: removing one or more of an adsorbed carbonate, bicarbonate, carboxylate, organic carbonate, or a mixture of two or more thereof from a surface of a supported catalyst, the supported catalyst comprising a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm and a hydrophilic support in contact with the particles; and simultaneously or thereafter adsorbing about 0.1 to about 10 monolayers of water on a surface of the support.
  • the invention provides a method for preparing or regenerating a preferential CO oxidation reaction (PROX) catalyst, comprising: removing one or more of adsorbed carbonate, bicarbonate, carboxylate, organic carbonate, or a mixture of two or more thereof from a surface of a supported catalyst, the supported catalyst comprising a plurality of Au or Ag particles having a size ranging from about 0.5 to about 20 nm and a hydrophilic support in contact with the particles; and simultaneously or thereafter adsorbing about 0.1 to about 10 monolayers of water on a surface of the support.
  • PROX preferential CO oxidation reaction
  • the removing comprises heating the supported catalyst to a temperature greater than about 150 °C for a time ranging from about 0 to about 16 hours.
  • the adsorbing is carried out thereafter and comprises contacting the supported catalyst with liquid H 2 0 or an H 2 0-containing inert gas or an H 2 0-containing reactive gas.
  • the removing comprises heating the supported catalyst to a temperature greater than about 150 °C, and wherein the adsorbing is carried out thereafter and comprises cooling the supported catalyst to a temperature of about 25 °C over a period of about 1 to about 24 hours while contacting the supported catalyst with an H 2 0-containing inert gas.
  • the removing comprises contacting the supported catalyst with a diluted mixture of H 2 and 0 2 gases at a temperature ranging from about 20 to about 400 °C.
  • the removing and simultaneous adsorbing comprise contacting the supported catalyst with a gaseous mixture of 02 N 2 /He/H 2 0/CO at a temperature ranging from about 20 to about 250 °C for a time ranging from about 0 to 5 hours. In some embodiments, the removing and simultaneous adsorbing comprise contacting the supported catalyst with a gaseous mixture of 02 N2/He/H20/CO at a temperature ranging from about 20 to about 100 °C for a time ranging from about 0 to 5 hours.
  • the active catalyst can be prepared in many ways and is not limiting.
  • supported gold or silver nanoparticles must be prepared on a hydrophilic support.
  • Numerous preparation methods are available in the literature; these methods include, but are not limited to, deposition-precipitation techniques (including urea deposition-precipitation), wetness impregnation techniques, strong electrostatic adsorption techniques, and colloid or nanoparticle deposition.
  • Commercially available catalysts can also be suitable precursors.
  • catalysts purchased from Strem Chemicals (Au/alumina, product number 79-0160; Au/titania, product number 79-0165; Au/zinc oxide, product number 79- 0170) as well as catalysts provided by MinTek.
  • the gold nanoparticles can range in size from 0.5-20 nm, but preferably are smaller than 10 nm and most preferably smaller than 5 nm.
  • Numerous supports can be used, including metal oxides (such as alumina, titania, silica, ceria, ZnO, iron oxides, manganese oxides etc.), mixed metal oxides, metal hydroxides, zeolites, clays, etc. with the key feature being that the support adsorbs and retains water under the reaction conditions.
  • any adsorbed carbonates must be removed and the water layer must be added.
  • Several methods can be used to prepare the active catalyst from the catalyst precursor, with the carbonate removal being the first critical step. This can be accomplished by heating to high temperatures under a flowing reactive or inert gas. A reactive mixture of H2 and 02 diluted in an inert carrier gas can also be passed over the catalyst at low to moderate temperatures to decompose the carbonates.
  • the water layer can be added by passing liquid water over the catalyst and drying in an inert gas or by equilibrating the catalyst surface with a gas containing water in an inert carrier gas.
  • water in an inert gas feed can be flowed over the catalyst at a low to moderate temperatures to decompose carbonates, hydroxylate the support surface, and deposit the water layer.
  • the catalyst can be prepared from a suitable supported gold nanoparticle precursor.
  • the thermal treatments used in catalyst preparation or regeneration often result in dehydroxylation of the catalyst surface and loss of adsorbed water. Therefore, the activation and pre-treatment typically performed immediately prior to contact with the reactive gas is particularly preferred in preparing the active composition of matter.
  • This class of pretreatments, which generate the active composition of matter enable the catalysts to generate high initial activity and can be used to regenerate a deactivated catalyst.
  • This general activation method can be summarized by the following elements:
  • the catalyst When the catalyst has been stored for prolonged times, and prior to PROX catalysis, the catalyst should be contacted with a moisture containing gas (no CO) to prepare the active composition of matter.
  • a moisture containing gas no CO
  • the catalyst may be contacted with a diluted mixture of H 2 and 0 2 gases, at temperatures ranging from 20 - 400 °C.
  • the catalyst may be contacted with a diluted mixture of H 2 , 0 2 , and H 2 0 gases, at temperatures ranging from 20 - 400 °C and cooled to the reaction temperature under a gas comprised of H 2 0 and an diluent gas (e.g. N 2 , air, etc.)
  • a gas comprised of H 2 0 and an diluent gas e.g. N 2 , air, etc.
  • the temperature used in the treatment described in the point 1 should be changed accordingly.
  • Supports that bind carbonates more strongly require the use of higher temperatures during catalyst pretreatment or regeneration.
  • the invention provides a process for CO oxidation in the presence of other gases using a PROX catalyst as described herein.
  • the CO oxidation process is carried out during the production of hydrogen gas via steam reforming.
  • the invention provides a process for oxidizing CO, comprising: contacting the PROX catalyst of the invention and a feed gas comprising CO, O2 and H2O at a temperature ranging from about 0 to about 300 °C, to thereby oxidize the CO.
  • the process further comprises removing O2 by contacting the gas with another catalyst.
  • the O2 removing catalyst is a hydrogenation catalyst.
  • the hydrogenation catalyst comprises a metal on an oxide support.
  • the metal comprises nickel, platinum, manganese, copper, iron, palladium or combinations thereof.
  • the oxide support comprises ⁇ 2, AI2O3, CeioAlOx, Ce 2 A10 x , Ce-Al-O x , Ce-Co-O, Ce-Cu-O x , CeFeOx, Ce-Fe-O x , Ce-Mn-Ox, Ce0 2 , Ce0 2 nanocrystal, Ce02 nanocube, Ce02 nanorod, Ce02 polyhedra, Ce02/ i02, Ce02-Co20 3 , Ce02- Fe 2 0 , CeZnOx, CeZrOx, Fe 2 0 , Fe-Ce-O x , Mn-Ce-O x , Mn0 2 -Ce0 2 , MnO x -Ce0 2 , T1O2, Zn-Ce0 2 , Zn-Ce-Ox, ZnO, ZnO-Fe20 3 , or a mixture of two or more thereof.
  • the oxide support is Ab0 3 . In some embodiments, the oxide support comprises S1O2. In some embodiments, the hydrogenation catalyst is Ni/Al20 3 . In some embodiments, the hydrogenation catalyst is Pt/Si02. In some embodiments, the process can utilize a single stage, dual-bed reactor system comprising the PROX catalyst and the second catalyst. In some embodiments, the process functions by having sufficiently high oxygen pressure to drive the CO oxidation reaction over the PROX catalyst to completion. The excess 0 2 needed to drive the CO oxidation reaction can then be removed using the O2 removing catalyst. In some embodiments, the second catalyst can be present at the bottom or the end of the reactor bed.
  • the O2 removing catalyst removes 50%, 60%, 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or substantially 100% of the remaining oxygen.
  • the process results in a substantially pure hydrogen effluent. In some embodiments, only about 2% of the hydrogen is sacrificed.
  • the feed gas comprises O2 and CO in an O2/CO molar ratio of about 1,000,000: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 100,000: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 10,000: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 1,000: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 100: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 75: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 50: 1.
  • the feed gas comprises O2 and CO in an O2/CO molar ratio of about 20: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 10: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 5: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio of about 1: 1. In some embodiments, the feed gas comprises O2 and CO in an O2/CO molar ratio ranging from about 0.2 to about 5.
  • the feed gas comprises H2O in an amount sufficient to maintain about 0.1 to about 10 monolayers of water on the surface of the support during said contacting.
  • the process produces a product gas comprising 1000 ppm or less of CO. In some embodiments, the process produces a product gas comprising 100 ppm or less of CO. In some embodiments, the process produces a product gas comprising 10 ppm or less of CO. In some embodiments, the process produces a product gas comprising 1 ppm or less of CO. In some embodiments, the process produces a product gas comprising 0.1 ppm or less of CO. In some embodiments, the process comprises an 0 2 selectivity for CO2 of 30% or greater. In some embodiments, the process comprises an O2 selectivity for CO2 of 40% or greater. In some embodiments, the process comprises an O2 selectivity for CO2 of 50% or greater.
  • the process comprises an O2 selectivity for CO2 of 60% or greater. In some embodiments, the process comprises an O2 selectivity for CO2 of 70% or greater. In some embodiments, the process comprises an O2 selectivity for CO2 of 80% or greater. In some embodiments, the process comprises an O2 selectivity for CO2 of 90% or greater.
  • the temperature ranges from about 0 to about 200 °C. In some embodiments, the temperature ranges from about 0 to about 175 °C. In some embodiments, the temperature ranges from about 0 to about 150 °C. In some embodiments, the temperature ranges from about 10 to about 150 °C. In some embodiments, the temperature ranges from about 20 to about 150 °C. In some embodiments, the temperature ranges from about 20 to about 100 °C. In some embodiments, the temperature ranges from about 20 to about 50 °C.
  • the feed gas further comprises one or more of non-condensable hydrocarbon, high dewpoint hydrocarbon, hydrocarbon, alkane, alkene, functionalized hydrocarbon, permanent gas, hydrogen, ammonia, N2, H 2 , air, He, Ar, C1-C10 hydrocarbon, or a mixture of two or more thereof.
  • the process produces a first product gas comprising 1000 ppm or less of CO; and which further comprises a second process for oxidizing said CO, the second process comprising: optionally, adding or removing one or more of O2, H 2 0, or both to or from the first product gas, to optionally form a second feed gas; contacting the first product gas or second feed gas with a second catalyst at a temperature ranging from about 0 to about 300 °C, to thereby oxidize said CO.
  • the second catalyst comprises the PROX catalyst as described herein.
  • the catalyst is distributed along a catalyst bed having an upstream portion and a downstream portion, and wherein the temperature of the upstream portion is higher than the temperature of the downstream portion. In some embodiments, the temperature gradually decreases between the upstream portion and the downstream portion.
  • the invention provides a dual stage process for using Au based catalysts to oxidize CO in non-condensable gas streams shown in Figure 5 (dew point > T36) comprising the steps of: decreasing initial CO concentration to 100 ppm, and finishing in a second stage until CO content is reduced to ⁇ 10 ppm.
  • the catalytic activity and selectivity is tuned by the control of adsorbed water on the catalysts. In some embodiments, the temperature is gradually decreased between sequential operating units.
  • activity and selectivity is preserved in the range of 0-150 °C, and wherein water is adsorbed on the catalyst.
  • gas mixture is comprised by high dew point hydrocarbons.
  • gas mixture is comprised by permanent gases 0 2 , N2, He, Ar, and their mixtures.
  • gas mixture is comprised of permanent gases and hydrocarbon mixtures.
  • gas mixture is comprised of high 3 ⁇ 4 concentrations mixtures. In some embodiments, where the catalyst is pretreated with water vapor/02 mixtures to achieve high catalytic activity.
  • the invention provides a single stage process for the preferential CO oxidation in gas streams using Au based catalysts exhibiting a gradual temperature decrease along the length of the bed.
  • high selectivity is afforded by performing the reaction in two serial steps, in which the main components are:
  • An initial CO oxidation reactor (stage 1, unit 36 in Figure 5) using a near stoichiometric amount of O2 (O2/CO 0.2 - 5) from air in which the resulting CO concentration is reduced to a range of 1000- 1 ppm.
  • the operating conditions for this reactor can be varied based on the specifics of the inlet feed and the requirements of the downstream process. Broad guidelines for this unit are as follows: a. The unit (unit 36) is operated at a higher temperature, which can be close to the outlet temperature of the preceding unit (typically, but not exclusively, a water-gas shift reactor). These temperatures are typically in the range of (50-200 °C). b.
  • the moisture content of the feed stream is equilibrated at the temperature of saturator 34, where T34 corresponds to the temperature necessary to obtain the desired water pressure (and therefore water coverage - typically 0.5-2 monolayer equivalents of water on the support) on the catalyst in Stage 1 (36), operated at T36.
  • T34 corresponds to the temperature necessary to obtain the desired water pressure (and therefore water coverage - typically 0.5-2 monolayer equivalents of water on the support) on the catalyst in Stage 1 (36), operated at T36.
  • the amount of added 0 2 can be varied based on the specifics of the feed and the operational requirements of the unit, but will typically have an O2/CO ratio in the range of 0.2-5.
  • stage 2 A second auxiliary stage (stage 2) in which CO content is lowered to ⁇ 1000 ppm.
  • the operation conditions in this stage are: a. Operating temperature (in unit 42) either (a) a low temperature, particularly when high selectivity is desired or (b) close to the delivery temperature necessary for the next downstream unit in the processing This temperature (T42) can be varied according to the process requirements, but will typically range from 0 to 100 °C ( Figure 5).
  • T42 can be varied according to the process requirements, but will typically range from 0 to 100 °C ( Figure 5).
  • the moisture content necessary for stream F may differ from the moisture content of stream C based on differences in the operating temperatures and the properties of the catalysts employed.
  • the primary function of saturator 2 (40) is to adjust the water content to the value necessary to obtain the desired water coverage on the catalyst in Stage 2 (42), typically 0.5-2 monolayer equivalents of water on the support.
  • the amount of added O2 can be varied based on the specifics of the feed and the operational requirements of the unit, but will typically have an O2/CO ratio in the range of 0.2-5.
  • Streams B and D can be used either to add water to the system or remove excess water, depending on the specifics of the inlet feed and the operating conditions.
  • H2 oxidation can be largely prevented, which improves the selectivity to values > 90%.
  • High selectivity in stage 2 is attained due to two factors: (i) water adsorbed on the support physically blocks the H2 binding sites at the metal- support interface, and (ii) H2 binding is an activated process, so employing lower temperatures prevents H2 adsorption / dissociation.
  • the dual stage system takes advantage of the higher activity at higher temperatures, using a small amount of residual CO and water to prevent 3 ⁇ 4 oxidation, and the higher intrinsic selectivity available at lower temperatures in stage 2.
  • the system can be operated under a variety of conditions and with a variety of catalysts.
  • the catalysts in stage 1 and stage 2 need not be identical, but certain qualities are required for high activity and selectivity:
  • the catalyst should consist of Au nanoparticles supported on a metal oxide or other material that can adsorb water.
  • the gold nanoparticles should be smaller than 10 nm in diameter, and preferably smaller than 5 nm in diameter. There should be sufficient remaining surface area on the support to adsorb water.
  • Supports may be either traditional amorphous supports or may consist of nanoscale support particles.
  • Micropore structures ( ⁇ 5 nm pore size) will favor capillary condensation, which may increase the amount of water adsorbed at a given humidity level.
  • 5- Promotors while not required, may be added (either to the support or to the Au) to improve catalyst performance.
  • Bi-metallic and mixed (combined) oxides may also be used.
  • the catalyst used in stage 1 does not necessarily need to be the same as the catalyst used in stage 2.
  • the catalyst and operating conditions used in Stage 1, particularly the water adsorption qualities, can be chosen based on the outlet conditions from the upstream unit. For relatively dry feeds and/or higher operating temperatures, the preferred catalyst will bind water strongly (or have a higher water adsorption capacity). For relatively wet feeds and/or lower operating temperatures, the preferred catalyst will bind water less strongly (or have a lower water adsorption capacity).
  • stage 2 The catalyst and operating conditions used in stage 2, particularly the water adsorption qualities of the catalyst, can be chosen based on the outlet conditions from Stage 1, the overall process requirements (CO tolerance, selectivity), and downstream requirements (temperature, CO content, and humidity). Catalysts with higher intrinsic selectivity for CO oxidation (over H 2 oxidation) will generally be preferred and operated at temperatures that maximize selectivity and H 2 throughput. For lower operating temperatures, catalysts with lower water adsorption strength (or lower adsorption capacity) relative to stage 1 will generally be preferred.
  • stage 1 for example, alumina, silica-alumina, vermiculite, etc.
  • stage 1 for example, alumina, silica-alumina, vermiculite, etc.
  • EMBODIMENT 1 Two stages operated in such way that the CO slip in stream D (after stage 1) ranges from 1000-1 ppm.
  • the specifics of the catalyst can be varied based on the humidity of the inlet feed. Alumina (better water sorbent) is preferred in the first stage and Titania is preferred in the second stage.
  • EMBODIMENT 2 Two stages operated in such way that the CO slip in stream D (after stage 1) ranges from 1000-1 ppm.
  • the specifics of the catalyst can be varied based on the humidity of the inlet feed.
  • Alumina better water sorbent
  • Titania is preferred in the second stage.
  • an additional H 2 or hydrocarbon oxidation catalyst can be placed to remove any remaining 02 from the process.
  • the specifics of this secondary catalyst can be varied based on the humidity of the inlet feed and the oxygen tolerance of the downstream process.
  • Typical oxidation catalysts are comprised of an active metal (e.g.
  • oxide support alumina, titania, silica, phosphate, etc.
  • active carbon alumina, titania, silica, phosphate, etc.
  • EMBODIMENT 3 One stage process with a single catalyst where temperature gradually decreases along the catalytic bed. Temperature and moisture in the top of the bed can be chosen to reach high CO conversion while temperature in the bottom is chosen in order to reach the desired CO slip. Excess of water in the bottom of the bed causes a under-optimal activity, but also limits H 2 oxidation. Weaker water sorbent support is preferred in this type of embodiment (e.g. T1O2).
  • EMBODIMENT 4 One stage process with a single catalyst where temperature gradually decreases along the catalytic bed. Temperature and moisture in the top of the bed can be chosen to reach high CO conversion while temperature in the bottom is chosen in order to reach the desired CO slip. Excess of water in the bottom of the bed causes a under-optimal activity, but also limits H 2 oxidation. Weaker water sorbent support is preferred in this type of embodiment (e.g. AI2O3 or T1O2). At the end of the second stage, an additional H 2 or hydrocarbon oxidation catalyst can be placed to remove any remaining 02 from the process. The specifics of this secondary catalyst can be varied based on the humidity of the inlet feed and the oxygen tolerance of the downstream process.
  • Typical oxidation catalysts are comprised of an active metal (e.g. Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, W, Re, Os, Ir, Pt, Au, Hg, etc.) supported on an oxide support (alumina, titania, silica, phosphate, etc.) or active carbon.
  • an active metal e.g. Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, W, Re, Os, Ir, Pt, Au, Hg, etc.
  • oxide support alumina, titania, silica, phosphate, etc.
  • EXAMPLE 1 Controlling Activity and Selectivity using Water in the Au-catalyzed Preferential Oxidation of CO in H 2
  • a typical benchmark goal for the PROX reaction is to reduce the CO concentration at the reactor outlet (hereafter referred to as the "CO slip") to 50 ppm with 0 2 selectivity to C0 2 > 50%. 1 3
  • the 50/50 goal We refer to this as the 50/50 goal.
  • Supported Au nanoparticles are well-known to be highly active CO oxidation catalysts 4"6 and notoriously poor hydrogenation catalysts. 7 They should be excellent PROX catalysts, but 20 years of research has produced very few catalysts capable of achieving the 50/50 goal (Fig. 6A).
  • a FOM value of 1 describes a catalyst and reaction conditions that meet the 50/50 goal.
  • Figure 6A plots several FOM values against the nominal activity for some of our experimental conditions. Approximately 60 literature reports are included (details in SI 3.3), most of which were collected at 80°C, the operating temperature of many fuel cell systems. 34 The literature results vary greatly, so nominal activities are normalized to the total amount of Au, making no adjustments for Au particle size. We are aware of only two reports that achieve the 50/50 goal, both using low space velocities and nominally dry feeds. 1 ' 8 By controlling the amount of water added to the reaction (vide infra) and using higher space velocities, we far surpass the 50/50 goal, and do so at space velocities 1-2 orders of magnitude larger than literature reports (Fig. 6 A, Table 8).
  • Figure 7 shows CO slip and O2 selectivity data for the experiments in Fig. 6A.
  • the experimental protocol SI 2.2-3 was critical to achieve high activity and selectivity, so catalysts were always equilibrated with 30 Torr water before initiating the reaction.
  • the water pressure Pmo was then systematically lowered, allowing the CO conversion to stabilize at each PH2O (generally 30 min).
  • Controlling the space velocity (SV), which is simply the flow rate normalized to the amount of catalyst, is critical to achieving high activity and selectivity.
  • SV space velocity
  • the reaction can operate at very high conversions (99.9%, ⁇ 10 ppm CO slip) while maintaining high O2 selectivity (> 80%); if the SV drops too low, O2 selectivity suffers (Fig. 7C).
  • the key elements of this mechanism are (i) the facile generation of reactive Au-OOH from 0 2 and a proton from water adsorbed at the metal- support interface, (ii) a very low reaction barrier between Au-OOH and Au-CO, and (iii) the rate limiting decomposition of Au-COOH. 5
  • the CO oxidation kinetics and H/D kinetic isotope effect for Au/Al 2 0 3 are essentially identical to Au/Ti0 2 , indicating the same mechanism is likely at work (SI 3.1).
  • Our results are largely consistent with the extensive PROX mechanistic work from the Behm 2 ' 29 and Piccolo 37 ; however, there are two important distinctions from their previous interpretations.
  • EXAMPLE 2 Supporting Information for "Controlling Activity and Selectivity using Water in the Au-catalyzed Preferential Oxidation of CO in H 2 "
  • the catalysts used in this study were commercial AUROliteTM samples (Au/Al 2 0 3 and Au/Ti0 2 ) purchased from AuTEK. These catalysts were pretreated by the manufacturer to ensure the particles were of appropriate size to be active for CO oxidation. The catalysts were crushed and stored in a dark refrigerator. Powdered silicon carbide (400 mesh) was purchased from Aldrich. The Au particles on the A11/AI2O3 catalyst were too small to be imaged by TEM. A sintered catalyst (500 C under H 2 for 4 hours) showed an average particle size of 2.2 nm. Gases (N 2 , He H 2 , 0 2 , and 5% CO/He) were 5.0 grade supplied by Praxair and used with no additional purification. Water was purified to a resistivity of 18.6 ⁇ with a Barnstead Nanopure system.
  • the catalysts are active with no further treatment; however, careful control of the reaction conditions is critical to maximize the resulting catalytic activity. This is due to the importance of surface water and carbonates:
  • Carbonates formation is closely related to the lack of water adsorbed on the catalyst and/or in the gas mixture. In both cases, decomposition of -COOH intermediates (on Au or on the support) seems to be intimately related to the presence of water 5 ⁇ 22 ⁇ 25 . Additionally, higher temperature pretreatments result in catalysts that form greater amounts of surface carbonates under reaction conditions 35 resulting in lower catalytic activity 52 .
  • catalysts (20-200 mg) are diluted in an inert material (S1O2, SiC, ⁇ - ⁇ 2 ⁇ 3 ) and tested in a continuous bed reactor apparatus.
  • a model gas reformate mixture (1-2% CO, 1-2% 0 2 , 50-60% H 2 , and 0-5% CO2, 20-200 mL/min) is passed through the catalyst bed.
  • CO PROX experiments are typically performed in the 20-100°C temperature range. The heating rate is not always reported, but is normally low, and varies in the range 0.2-l°C/min 37 ' 54 .
  • FIG. 11 plots the CO conversion for a Au/Ah0 3 catalyst (60 mg) at 40°C when a slow heating ramp (2 °C/min ( «)) is used compared to the conversion when the reacting mixture is contacted with the catalyst at 40 °C with no ramping ( A ). All other conditions were the same. This difference in activity for the same catalyst is attributable to two main causes:
  • the catalyst surface must have a high water coverage before and during the reaction.
  • Thermal pretreatments should be carried out at temperatures as low as possible.
  • Reaction temperature must be reached quickly by accelerating the heating ramp of the catalytic bed. This can be achieved by preheating the furnace before bringing the reactor on-line.
  • the CO oxidation reactor consisted of a home-built laboratory scale single pass plug-flow micro-reactor.
  • the reaction zone consisted of finely ground fresh catalyst (5-100 mg) diluted in 1200 mg of silicon carbide. Gas flows were controlled with four electronic low-pressure mass flow controllers (Porter Instruments).
  • the composition of the feed and reactor effluent (CO and C0 2 ) were determined using a Siemens Ultramat 23 IR gas analyzer, which included an electrochemical O2 analyzer.
  • No thermal pre-treatment was performed to the Au/Al 2 0 3 catalyst.
  • the reaction temperature (20-80 °C) was maintained with a water bath pumped through a dewar. The water bath was always heated to the reaction temperature before immersing the U-tube reactor in the dewar.
  • the catalyst was then stabilized in the reactive atmosphere until steady-state conditions were reached (with no change in CO oxidation rate, ⁇ 30 min).
  • the water pressure in the feed gas was changed by decreasing the temperature of the saturator; the lowest attainable value was approximately 1 mTorr (the equilibrium vapor pressure at the temperature of dry ice, - 78.5 °C).
  • CO reaction order CO kinetic dependence was performed using five CO concentrations (0.45, 0.73, 1.0, 1.24, and 1.46% V oi) with variable concentration of water in the feed. 0 2 content was held constant at 1.35%.
  • OH and adsorbed H 2 0 on T1O2 and AI2O3 can be interchanged in-situ under carefully controlled conditions.
  • T1O2 isotope exchange has been described in Ref 5 . Briefly, at 20°C, D2O containing N2 flow (100 mL/min) interchanges OH (to OD) and H2O (to D2O) from T1O2 in a 30 min treatment. Additional treatment for 30 minutes under flowing N2 eliminates excess D2O.
  • the interchange process is slower compared to T1O2 and requires either longer treatment times when interchange occurs at 20°C, or higher temperatures maintaining the same interchange time (30 min).
  • a liquid nitrogen trap was used to remove impurities from the CO tank (UHP Grade, from Air Products).
  • the entire gas handling system was purged with CO three times before exposing the sample. After collecting a background spectrum, the sample was exposed to 20 Torr CO, and the surface was allowed to equilibrate for 5-10 minutes; previous work has shown this is ample time for CO equilibration on Au catalysts 41 ⁇ 56 ⁇ 57 . An infrared spectrum was recorded and the pressure in the cell was slowly decreased to the next pressure.
  • the sample was first dried under vacuum at room temperature. CO (20 Torr) was added to the cell and allowed to equilibrate for 5-10 minutes. Once at equilibrium, an IR spectrum was collected. The CO pressure was then incrementally decreased with IR spectra being collected at each equilibrated pressure of CO. Next, the cell was evacuated, 0.1 Torr of water was added to the chamber, and allowed to equilibrate. CO was then incrementally added to the chamber and IR spectra collected at each pressure of CO. This general procedure was repeated for higher pressures of added water.
  • Water adsorption isotherm measurements were measured at four different temperatures (20, 30, 40 and 50 °C) using a Micromeritics 3Flex volumetric adsorption apparatus. Prior to measuring the isotherms, the catalyst (100 mg) was evacuated at a rate of 10 mm Hg/s to less than 0.01 ⁇ Hg. The catalyst was first heated to 90°C at 5°C/min and held at that temperature for 30 minutes. A second temperature ramp was used to heat the samples (in vacuo) from 90 to 120°C using a rate of 5 °C/min. The catalyst was then held at 120°C for a minimum of eight hours; the pressure did not exceed 0.01 ⁇ Hg during the second stage of the pretreatment.
  • the catalyst was cooled to the adsorption experiment temperature under vacuum.
  • the sample temperature was maintained using a Neslab recirculating bath coupled to a Cryofab dewar.
  • the water source temperature was maintained at 43 ⁇ 0.1 °C and the instrument manifold was maintained at 45 ⁇ 0.02 °C.
  • small doses of water (0.05 mmol/g) were equilibrated with the sample to develop the high resolution adsorption and desorption isotherms. Free-space was measured after the analysis to avoid any stray gas interference or exposure prior to the water adsorption.
  • Rate-determining decomposition of Au-COOH accompanied by a proton transfer from Au-COOH to water adsorbed on the support.
  • reaction kinetics data A more detailed comparison of the reaction kinetics data is found below; for convenience, we have compiled the key kinetic parameters in Table 2.
  • the overall reaction kinetics are essentially the same for both catalysts, indicating that both materials catalyze CO oxidation via the same, or very similar, reaction mechanisms.
  • Figure 15 shows that reaction rate correlates extremely well with the amount of water adsorbed on the catalysts; additionally, the reaction orders for adsorbed water are substantially larger than the reaction orders for the water in the gas phase.
  • FIG 16 shows the results for the KIE experiment for CO oxidation on AU/T1O2 (A-left) and AU/AI2O3 (B-right).
  • Six separate experiments were performed and averaged with H2O saturated (A blue data, O) and D2O saturated ( « red data, D) samples.
  • the measured KIE values (1.84 and 1.81 for T1O2 and AI2O3, respectively) are essentially the same for the two catalysts.
  • the magnitude is consistent with a primary KIE, indicating that O-H(D) bond cleavage is involved in akinetically important step.
  • KIE values are the same for both catalysts, some differences are apparent.
  • the catalytic rate for AU/T1O2 is roughly three times faster than for AU/AI2O3 after 60 min time-on-stream (TOS). This difference is also apparent in the different scales in the y-axes of Fig. 16. Second, the deactivation rate is more pronounced for AI2O3; these two elements could be related and are likely attributable to greater carbonates formation on AI2O3 at the very first moments of catalysis.
  • Figure 17 shows that higher CO concentrations (> 1%) decrease the overall reaction rate; consequently, the apparent reaction orders are negative.
  • slightly negative reaction orders can be interpreted as the saturation of the metal surface by adsorbed CO causing a 'poisoning' of the oxygen activation sites.
  • the water pressure increases the overall reaction rate substantially, it has a minimal effect on the CO reaction order.
  • Figure 18 illustrates the effect of water produced from H 2 oxidation on the CO oxidation reaction during PROX.
  • H 2 blue data
  • CO oxidation activity drops precipitously when water is removed from the system and reaches a maximum at about 4 Torr.
  • PROX red data
  • the maximum CO oxidation activity occurs at much lower added Pmo (ca. 1.5 Torr) and does not decrease substantially when water is removed.
  • Table 1 estimates the actual support water coverage (Gmo) by accounting for the water produced by the unselective oxidation of H 2 . For simplicity and clarity, we evaluated the total water on the surface at the CO oxidation activity maximum. This value was estimated as follows: • The 0 2 conversion and selectivity data were used to calculate the total O2 converted.
  • the FOM is a nominal measure of both activity and selectivity; high selectivity and high CO oxidation activity (represented by a low CO slip) result in larger values for the FOM. Since the FOM describes performance under a given set of conditions (space velocity, temperature, feed composition, etc.) a single catalyst will have a FOM value for every set of conditions tested.
  • the FOM formally has units of %/ppm due to the activity definition in terms of CO slip which, in this case, is more useful than a unitless measure, such as CO conversion.
  • a unitless measure such as CO conversion.
  • the FOM is formally boundless, in practice it is limited by the precision in the CO slip measurement, which is about 1 ppm CO for our experiments.
  • the lower limit approaches 0; thus the practical range of the FOM, at least for our experiments and those we have found in the literature, is 0-100 %/ppm.
  • Tables 3-7 were collected using our system and the AU/AI2O3 catalyst described above. Table 8 compiles numerous reports from the literature.
  • the powdered catalysts were finely ground using a mortar and pestle.
  • Powder mounting substrates were prepared by fastening a 5mm x 5mm square of 3M double-sided tape to a piece of Si wafer with dimensions of about l x l cm. The catalyst powder was pressed into the surface of the 3M tape in a manner that completely covered the adhesive. Each powder sample was individually mounted.
  • Loose particles were removed from each sample mount by blowing the surface off with a jet of dry nitrogen.
  • Four or five powder mounts were placed on the sample bar for analysis. Each mount was secured to the sample bar with a 5mm x 5 mm piece of 3M double-sided tape, so the individual mounts are electrically insulated from the sample bar. All spectra were acquired with the charge neutralizer on. Analytical chamber pressures were in the mid 10-8 torr range.
  • the x- ray gun anode voltage and current were 14 keV and 20 niA respectively.
  • Survey scans were acquired at a pass energy of 80 eV, a step size of 0.5 eV, and dwell time of 150 ms.
  • High-resolution Au 4f spectra were acquired at a pass energy of 20 eV, a step size of 0.5 eV, and a dwell time of 2500 ms.
  • X-ray Diffraction (XRD) Data The X-ray diffraction (XRD) pattern was collected on a PANalytical Empyrean diffractometer with Cu K « radiation at 45 kV and 40 mA. Fixed slit para- focusing geometry was utilized with 0.04 radians soller slits, 10 mm beam mask, a 0.25° divergence and a 0.5° anti-scatter slit on the incidence side. Divergent optics included a 0.25° anti-scatter slit, 0.04 radians soller slits, and a nickel filter. A PIXcel detector in ID scanning mode with PSD length of 3.35° was used.
  • Figure 23 A shows the adsorption isotherms for wfkO on the two catalysts.
  • the isotherms are well described by the Langmuir adsorption model; linear Langmuir plots and extracted equilibrium constants for wfkO binding to the catalysts (K W H2o) are shown in Figure 23B.
  • the equilibrium constants are essentially the same; the small differences between the two measured values are unlikely to account for the differences in catalytic activity.
  • Au is widely considered to be hydrophilic *ref and control experiments indicate that the observed adsorption is consistent with adsorption on the support and not on Au.
  • Figure 24 shows the results of two studies. First, we flowed a 1 % CO/N2 gas feed over a dried Au/Ti02 sample to allow the CO to adsorb onto the catalyst. The feed was then passed through a water saturator and the saturator temperature was adjusted to yield several different water pressures. The sample was equilibrated at each water pressure, and an infrared spectrum was recorded.
  • the second experiment similarly shows the important relationship between the Au-CO binding and the amount of water on the support.
  • the catalyst was first saturated with a 1 % CO + H20/ N2 gas feed. The water was then removed from the feed and the catalyst was dried in flowing 1% CO/N2. Infrared spectra were collected during drying and both the vCO and ⁇ peaks were monitored over time. As Figure 24B clearly shows, there is an essentially linear relationship between the amount of water adsorbed on the support and the amount of CO adsorbed on the gold.
  • Gold is widely considered to be hydrophilic, and we see no evidence to support the conclusion that water adsorbs directly onto the Au. Rather, we believe that these results are consistent with a physical blocking of CO adsorption sites at or near the metal-support interface. As greater amounts of water are adsorbed onto the support, more of these sites are blocked, and fewer CO adsorption sites remain. In a sense, this can be thought of as a wetting of the catalyst surface and, at high enough water pressures, the water layer can become deep enough that the Au nanoparticles are "flooded" with water and can no longer readily adsorb CO.
  • reaction kinetics water, CO, and O2 reaction orders; KIE
  • AU/AI2O3 and AU/T1O2 the two catalysts almost certainly operate with essentially the same reaction mechanism. This has important implications for other mechanisms suggested in the literature, primarily mechanisms that invoke a reduction of the titania support.
  • the reaction kinetics indicate that, while titania is a reducible support, that reducibility (which leads to O vacancies on the surface) does not appear to play an important role in CO oxidation catalysis under the reaction conditions that we have studied.
  • the logic behind this conclusion is as follows: Alumina cannot be reduced under the reaction conditions we have studied; therefore, oxygen vacancies cannot be invoked in the reaction mechanism for Au/AhCb.
  • Double reciprocal plots of O2 dependence data collected at various pressures of added water can then be used to extract KR and O MAX kinetic parameters that describe the catalysts under those specific conditions. These parameters are plotted as a function of the added water content in (expressed in terms of the coverage of weakly bound water) in Figure 27, and allow for a number of conclusions regarding each catalyst.
  • the KR values are relatively constant for each catalyst, suggesting that added water has little effect on the electronics of the active site. This is consistent with the proposed mechanism, and indicates water' s primary role as a proton donor and acceptor.
  • the active site kinetic treatment indicates that the Au/A1203 and Au/Ti02 catalysts have very similar intrinsic reactivity for CO oxidation.
  • the primary difference between the two catalysts is in the number of active sites. This difference is clearly tied to the amount of weakly adsorbed water on the catalyst; however, the strength of adsorption of water on the catalysts is identical (Figure 23).
  • the only significant difference we have observed between the two catalysts that might be tied to the difference in activity is the much slower rate of H/D exchange over Au/A1203. This suggests that the differences in activity might be indirectly tied to the reactivity of either the surface hydroxyl groups, or some other adsorbed surface species.
  • water can adsorb as an in-tact molecular species or at a bridging Ti-O-Ti site, creating two surface hydroxyls.
  • ⁇ ( ⁇ ) bending vibration at -1640 cm “1 as a function of water pressure which can only be due to molecular water, the IR spectra allow us to readily distinguish between these two possible adsorption modes.
  • Figure 23 shows adsorption isotherms for weakly adsorbed water measured by infrared spectroscopy. Although there are large differences in the total amount of water adsorbed, these are largely attributed to the differences in the support surface area. Linear Langmuir plots of the data show that the adsorption thermodynamics are essentially identical for the two catalysts. This is perhaps not surprising - the adsorption energy for water adsorbing as a molecular species on surface hydroxyls, which is dominated by hydrogen bonding interactions, might be expected to be relatively insensitive to the underlying metal oxide structure. We previously investigated pretreatment effects on the catalytic activity of Au/Ti02, and found that surface carbonates appeared to play an important role in the catalytic activity.
  • EXAMPLE 4 Oxidation of 1 % CO in presence of 60% H 2 at 50 °C using A11/AI2O3 catalyst.
  • This example shows that the system can be operated as a single stage reactor. Low CO slips can be achieved; however, O2 selectivity, while good, is not as high as when the system is operated with a second stage catalyst at lower temperature.
  • EXAMPLE 6 Oxidation of 1% CO in presence of 60% H 2 at 40 °C using A11/AI2O3 catalyst. Effect of pretreatment of the catalysts.
  • NaOH DP 1900 64 40 1.7 Au/A1203 1 hr @ 100 °C
  • EXAMPLE 8 Oxidation of 1% CO in presence of 60% H 2 at 50 °C using Au/ZnO catalyst
  • EXAMPLE 10 PROX catalysis with hydrogen oxidation catalyst at the bottom of the bed.
  • This single-stage, dual-bed reactor functions by having sufficiently high oxygen pressure to drive the CO oxidation reaction over the Au and water catalyst to completion.
  • the Ni catalyst at the bottom of the bed removes the remaining oxygen, leaving a pure hydrogen effluent while sacrificing only 2% of the hydrogen.

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Abstract

La présente invention concerne un catalyseur de réaction d'oxydation de CO préférentiel (PROX), comprenant : une pluralité de particules d'Au ou d'Ag ayant une taille allant d'environ 0,5 à environ 20 nm ; un support hydrophile en contact avec les particules ; et d'environ 0,1 à environ 10 monocouches d'eau sur une surface du support.
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CN108514881A (zh) * 2018-04-12 2018-09-11 大连理工大学 一种用于NH3催化氧化的纳米棒状结构的Cu-Ce催化剂、制备方法以及应用
CN109078642A (zh) * 2018-07-16 2018-12-25 东南大学 一种花型纳米金复合金属氧化物催化剂及其制备方法和应用
CN109603837A (zh) * 2019-01-18 2019-04-12 中国科学院青岛生物能源与过程研究所 一种用于糠醛液相加氢的Cu/Ce/Co催化剂的制备方法
CN113198485A (zh) * 2021-05-18 2021-08-03 贵州大学 一种铝铈复合氧化物催化剂及制备方法及应用
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CN116920868A (zh) * 2023-03-29 2023-10-24 中国计量大学 一种多级式钴锰尖晶石阵列光热催化剂的制备方法与应用

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CN107519861A (zh) * 2017-08-10 2017-12-29 中国科学院生态环境研究中心 一种铈锰复合氧化物催化剂、其制备方法及用途
CN107824199B (zh) * 2017-11-20 2020-02-07 山东理工大学 醛类一步氧化酯化合成酯的磁性纳米金催化剂及其制备方法和应用
CN107824199A (zh) * 2017-11-20 2018-03-23 山东理工大学 醛类一步氧化酯化合成酯的磁性纳米金催化剂及其制备方法和应用
CN108514881A (zh) * 2018-04-12 2018-09-11 大连理工大学 一种用于NH3催化氧化的纳米棒状结构的Cu-Ce催化剂、制备方法以及应用
CN108514881B (zh) * 2018-04-12 2020-11-03 大连理工大学 一种用于NH3催化氧化的纳米棒状结构的Cu-Ce催化剂、制备方法以及应用
CN109078642A (zh) * 2018-07-16 2018-12-25 东南大学 一种花型纳米金复合金属氧化物催化剂及其制备方法和应用
CN109078642B (zh) * 2018-07-16 2021-06-01 东南大学 一种花型纳米金复合金属氧化物催化剂及其制备方法和应用
CN109603837A (zh) * 2019-01-18 2019-04-12 中国科学院青岛生物能源与过程研究所 一种用于糠醛液相加氢的Cu/Ce/Co催化剂的制备方法
CN109603837B (zh) * 2019-01-18 2021-12-31 中国科学院青岛生物能源与过程研究所 一种用于糠醛液相加氢的Cu/Ce/Co催化剂的制备方法
WO2022126842A1 (fr) * 2020-12-14 2022-06-23 苏州大学 Procédé de traitement thermique à basse température de toluène à l'aide d'un matériau composite ayant une structure cœur-écorce de microfeuille de cecuox bimétallique / nanofeuille de nio ternaire
US12539506B2 (en) 2020-12-14 2026-02-03 Soochow University Method for low-temperature heat treatment of toluene by using composite material having ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure
CN113198485A (zh) * 2021-05-18 2021-08-03 贵州大学 一种铝铈复合氧化物催化剂及制备方法及应用
CN116920868A (zh) * 2023-03-29 2023-10-24 中国计量大学 一种多级式钴锰尖晶石阵列光热催化剂的制备方法与应用

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