EP0756579A1 - Nichtstöchiometrisches tungstencarbid - Google Patents

Nichtstöchiometrisches tungstencarbid

Info

Publication number
EP0756579A1
EP0756579A1 EP95917401A EP95917401A EP0756579A1 EP 0756579 A1 EP0756579 A1 EP 0756579A1 EP 95917401 A EP95917401 A EP 95917401A EP 95917401 A EP95917401 A EP 95917401A EP 0756579 A1 EP0756579 A1 EP 0756579A1
Authority
EP
European Patent Office
Prior art keywords
compound
tungsten
carbon
advantageously
hydrogen
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP95917401A
Other languages
English (en)
French (fr)
Inventor
Maurice Charpenel
Evelyne Chassagneux
Roland Jacquot
Gérard Mignani
Marcel Vialon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rhodia Chimie SAS
Original Assignee
Rhone Poulenc Chimie SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rhone Poulenc Chimie SA filed Critical Rhone Poulenc Chimie SA
Publication of EP0756579A1 publication Critical patent/EP0756579A1/de
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/20—Carbon compounds
    • B01J27/22—Carbides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/90—Carbides
    • C01B32/914—Carbides of single elements
    • C01B32/949—Tungsten or molybdenum carbides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • the present invention relates to new catalytic compositions based on tungsten and carbon. It relates more particularly to compositions which deviate from the atomic ratio between tungsten and carbon of 1.
  • tungsten carbide is an oxidation-reduction, and in particular hydrogenation, catalyst having particular qualities
  • this catalyst is also known as a reduction or decomposition catalyst for the various oxides of nitrogen emitted by internal combustion engines and in particular petrol engines. This effect is particularly mentioned in the "chemical abstracts" volume 119, 1993 N ° 119: 124072 v.
  • the use of this catalyst comes up against a double difficulty; on the one hand, the catalytic power reduced to the square meter remains relatively low and, on the other hand, tungsten carbide is known for its hardness, which makes it difficult to grind and therefore its reduction into fine particles of high specific surface.
  • one of the aims of the present invention is to provide a carbon-based and tungsten-based compound having good catalytic characteristics, in particular for hydrogenation reactions.
  • Another object of the present invention is to provide a compound of the above type having catalytic powers greater than those of the usual compounds of tungsten carbide (WC and to a lesser extent W2C).
  • Another object of the present invention is to provide a compound of the above type having a naturally high specific surface.
  • Another object of the present invention is to provide synthetic methods making it possible to obtain the compounds of the above type.
  • Another object of the present invention is to provide uses in which the properties of the compounds of the above type are particularly useful.
  • the catalysts chosen are compounds based on carbon and tungsten, according to the present invention, which are not thermodynamically stable.
  • non-thermodynamically stable means the tungsten compounds which exhibit a non-reversible transformation when they are subjected to differential thermal analysis (or ATD) at a temperature below about 2000 degrees Celsius.
  • the catalytic activity is all the better as the tungsten carbide phase of the catalyst approaches the amorphous state. More specifically, the amorphous character is determined by the size of the coherent diffraction domain, size is sometimes assimilated to that apparent of any crystallites (generally of composition relatively close to that of WC), "measured” by the Scherrer method (which is briefly recalled in the experimental part of this description). In the following description, for simplicity, reference will be made not to the size of the coherent diffraction domain, but rather to the apparent size of the possible crystallites.
  • the compounds according to the present invention which will be referred to collectively hereinafter, in the present description, under the term of no stoichiometric tungsten carbide, advantageously contain a metalloid content (in addition to carbon) at least equal to 0 , 5% by mass.
  • metalloids can be either isolated metalloids or a mixture of metalloids.
  • the metalloids are advantageously chosen from the metalloids of columns V VI, preferably from the elements of periods (lines) 2 and 3.
  • the low constraint (advantageous minimum content (s) or preferred) on the metalloids is met by nitrogen or oxygen alone or by one of their mixture.
  • the total content of metalloids does not exceed 20% (by mass) (a significant figure, preferably 2). More specifically, the content of metalloid (s) is advantageously less than 15%, preferably more than 4%.
  • the zone in which the carbon is over-stoichiometric is also interesting provided, of course, that the stoichiometry of the defined compounds is avoided as W2C3 from which it is necessary to deviate from the percentage of carbon as has already been specified above
  • the preferred domains are between 1.01 and advantageously between 1.01 and 7/8, preferably between 1.02 and 1, 4.
  • the catalyst is preferably in the form of high specific surface area. It may be in the form of a powder or it may be present in the form of a surface layer the thickness of which is at least 50 angstroms (5 nanometers) on various supports.
  • titan dioxide TiO 2
  • vanadium carbide as well as the sources of tungsten used for the synthesis of non-stoichiometric tungsten carbide compounds according to the present invention.
  • another object of the present invention is to provide a process for the synthesis of the non-stoichiometric compounds of tungsten carbide according to the present invention.
  • Carbonaceous gases are chosen from volatile carbon compounds and in particular from light hydrocarbons; carbon dioxide can also be carbon oxides, namely either carbon monoxide often called carbon monoxide, or mixtures of carbon monoxide, carbon dioxide (or carbon dioxide), and hydrogen more commonly known as the name of gas in water, it is preferable to work with a large excess of hydrogen in order to avoid precipitation, on the surfaces, of carbon which would then have to be eliminated by the operation called decocking which will be described subsequently, carbon which by covering the catalytically active surfaces will reduce the effectiveness of the non-stoichiometric carbides according to the invention. It is preferable that it has at least 1 molecule of hydrogen gas per carbon atom of the carbon gas. Preferably, we place our at a number of hydrogen molecules equal to approximately 10 (u significant figure) molecules of gaseous hydrogen per carbon present in the carbonaceous ga.
  • the total pressure is indifferent but, for safety reasons, we generally proceed at low pressures, most often at a pressure close to atmospheric pressure.
  • the temperature at which step b) is carried out is advantageously between 600 and 1200 ° C., preferably between 900 and 1100 ° C.
  • the tungsten substrates are chosen from metalloid derivatives of tungsten.
  • tungsten halides including mixed halides or oxyhalides
  • tungsten pnictures such as tungsten nitride
  • tungsten chalcogenides such as oxides and sulfides
  • all the elements which make it possible to switch to tungsten metal as well as the latter itself Special mention must be made of tungsten oxides, and in particular of tungsten trioxide (WO3), and the salts of tungstic acid; salts, the catio of which advantageously gives volatile compounds during the reaction, such as, for example, ammonium tungstates, including alkylmonium tungstates.
  • step b The temperature of step b is carried out at a temperature lower than that of sintering.
  • the duration of step b) is, for information, between 1 and 50 hours, preferably from 3 hours to 20 hours. It is very desirable that step b) be followed by a later step c) called d unstacking.
  • This step c) is carried out using hydrogen either pure or mixed with an inert gas under the conditions of the experiment.
  • the hydrogen can be replaced by "hydrogenogenic" gases, that is to say capable of generating hydrogen under the conditions of step c).
  • these hydrogenogenic gases there may be mentioned ammonia (NH3). Mention may also be made of hydrazine.
  • the PH2 / P CH4 ⁇ St ratio advantageously greater than 500, preferably 1000, preferably 10 4 .
  • the duration of this stage depends on the manner in which stage b was carried out and is generally greater than 1 hour.
  • the temperature at which step c) is carried out is advantageously between 600 and 1200 ° C., more advantageously between 700 and 1100 ° C., and preferably between 700 and 900 ° C.
  • the method according to the present invention can include a step d), but optional, of removing pyrophoricity.
  • This operation is carried out at ambient temperature (approximately 20 ° C.) by bringing the product thus obtained into contact with a mixture of gases containing an inert gas with respect to the product according to the invention and a little oxygen, the partial pressure is preferably at most equal to 5%, advantageously at most equal to 2% of atmospheric pressure, the contact is maintained until the property disappears substantially.
  • Another object of the present invention is to provide another type of process which consists in coating fine particles of tungsten products which will serve as substrates.
  • Preferred is ammonium tungstate mixed with a blowing agent, for example capable of giving a gas at high temperature.
  • Preferred here is di-ammonium carbonate with a polyamide or polyacrylonitrile dissolved in DMF.
  • the compound is then subjected to heating at a temperature of between 100 and 300 ° C., preferably between 150 and 250 ° C., then to partial pyrolysis advantageously under conditions close to those of step c), that is to say at the temperatures indicated and preferably in the presence of hydrogen.
  • the compounds thus obtained are generally over-stoichiometric in carbon and require decocking.
  • Another object of the present invention is to provide a synthesis process in which the non stoichiometric tungsten carbides according to the present invention are used.
  • a hydrogenatable organic substrate is subjected to hydrogenation in the presence of tungsten n stoichiometric carbide according to the present invention; the partial pressure of hydrogen advantageously between 1 and 200 bar, preferably between 2 and 100 bar.
  • Hydrogenation gives particularly good results in the liquid phase with reactive com, a composition comprising a non-stoichiometric tungsten carbide suspended in a liquid phase (this phase can be or comprises the substrate the hydrogenated product) with a gaseous phase containing hydrogen under partial pressure as indicated above, preferably between 5 and 50 bar (in this description the bar is considered to be equivalent to the atmosphere or to 1 Pascals).
  • the hydrogenatable substrates are advantageously chosen from the derivatives comprising a nitrogen capable of being hydrogenated, in particular the derivatives where the nitrogen e linked to non-aliphatic carbon atom, such as those where the nitrogen is linked to carbon atom of hybridization sp 2 (in particular the case of aromatic carbons).
  • non-stoichiometric tungsten carbide can be used for depollution and in particular for reducing the nitrogen oxide content of various gaseous mixtures discharged into the atmosphere.
  • This reduction is obtained by bringing nitrogen oxides in the gas phase into contact with a reducing gas such as hydrogen (or a source of hydrogen such as hydrocarbons) in the presence of a non-stoichiometric tungsten carbide according to the invention. .
  • a reducing gas such as hydrogen (or a source of hydrogen such as hydrocarbons) in the presence of a non-stoichiometric tungsten carbide according to the invention.
  • a catalyst comprising a non-stoichiometric tungsten carbide can be placed on the exhaust line.
  • a catalyst comprising a non-stoichiometric tungsten carbide can be placed on the exhaust line.
  • Diffraction results from the interaction of radiation with matter.
  • an electromagnetic wave hits an atom, its electrons undergo vibrations of the same frequency as the incident wave.
  • the absorption and re-emission of atoms in a periodic lattice constitute X-ray diffraction.
  • Bragg's law of diffraction which results from the particular optical and crystallographic conditions, gives the maxima of the diffracted intensity.
  • Three aspects of such a maximum interest the analyst the position of the peak, its intensity and its width.
  • the third point makes it possible to determine certain characteristics of the grain size.
  • the divergence and dispersion in wavelength of the incident X-ray beam, the absorption and the surface state of the sample, the width of the analysis slit, etc. are all factors so-called instrumental enlargement.
  • the size and deformation of the crystals cause a widening of the so-called intrinsic profiles. The smaller the crystals, the greater the contribution to the widening of the peak.
  • enlargement is an increasing function of the deformation.
  • the experimental profile is therefore the convolution of the instrumental profile and the intrinsic profile.
  • All the methods for calculating the size D of the crystallites are based on the mathematical modeling of the diffraction peaks. Two types of parameters are mainly used: - The width at mid-height, FWMH, and or the integral width, b, of the peak (width of a rectangle of the same height and the same area as the peak considered) (d Scherrer method).
  • the angular widths are the widths at mid-height of the peaks (101) and (001)
  • Tungsten oxide WO3 from the company March and having an apparent density of 1 is dried under nitrogen at 550 ° C for 10 hours then fueled at 600 ° C in a CH4 / H2 mixture (20/80 by volume) for 11:00. It then undergoes a "decocking" at 800 ° C under H2 for 10 hours. After cooling, the sample is taken for analysis; the oxygen and carbon contents are measured by high temperature pyrolysis followed by an analysis of the gases formed (C ⁇ 2). The tungsten content is obtained by difference.
  • the catalytic activity of the carbide obtained is determined by reduction of nitrobenzene to aniline the value given in the tables represents the catalytic power expressed in grams of nitrobenzene converted per hour and per gram of catalyst in an autoclave under 20 bar of hydrogen (2.10 6 Pascals), at 100 ° C. the density is measured by helium pycnometry.
  • Example N ° 6 2 p.m. to 1000 ° C 11 a.m. to 800 ° C 43 1.03 0.65
  • the compound is then heated in an inert atmosphere at 1000 ° C for ten hours.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Catalysts (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Carbon And Carbon Compounds (AREA)
EP95917401A 1994-04-18 1995-04-13 Nichtstöchiometrisches tungstencarbid Ceased EP0756579A1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9404588 1994-04-18
FR9404588A FR2718727B1 (fr) 1994-04-18 1994-04-18 Carbure de tungstène non steochiométrique.
PCT/FR1995/000492 WO1995028352A1 (fr) 1994-04-18 1995-04-13 Carbure de tungstene non st×chiometrique

Publications (1)

Publication Number Publication Date
EP0756579A1 true EP0756579A1 (de) 1997-02-05

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP95917401A Ceased EP0756579A1 (de) 1994-04-18 1995-04-13 Nichtstöchiometrisches tungstencarbid

Country Status (5)

Country Link
EP (1) EP0756579A1 (de)
JP (1) JPH09511980A (de)
AU (1) AU2348295A (de)
FR (1) FR2718727B1 (de)
WO (1) WO1995028352A1 (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19628160A1 (de) * 1996-07-12 1998-01-15 Studiengesellschaft Kohle Mbh Verfahren zur Herstellung von Übergangsmetallcarbiden sowie deren Verwendung als Katalysatoren
AT3064U1 (de) * 1998-12-28 1999-09-27 Plansee Tizit Gmbh Gaskarburierungsverfahren zur herstellung von reinem wc-pulver

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57191216A (en) * 1981-05-22 1982-11-25 Hitachi Metals Ltd Preparation of nonoxide powder
JPH01502427A (ja) * 1986-08-26 1989-08-24 エス・アール・アイ・インターナシヨナル 遷移金属炭化物およびその製造方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9528352A1 *

Also Published As

Publication number Publication date
FR2718727B1 (fr) 1996-07-12
JPH09511980A (ja) 1997-12-02
WO1995028352A1 (fr) 1995-10-26
AU2348295A (en) 1995-11-10
FR2718727A1 (fr) 1995-10-20

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