OA12069A - Surface catalyst infra red laser. - Google Patents

Abstract

A process and apparatus are provided for the generation of laser radiation by providing a fuel (105), such as methanol, ethanol, carbon monoxide and/or hydrogen, and air (106) to a catalyst (102), such as platinum, which is located beneath a polychromatic resonant optical cavity formed by laser mirrors (107) and (108). The catalyst surface is flooded with adsorbed fuel radicals, leaving relatively few sites for oxygen adsorption. Under this condition, the oxygen dissociates into two oxygen atoms or free radicals with approximately one electron volt of energy (i.e. "hot atoms"). These "hot atoms" of oxygen find fuel radicals as collision partners and form reaction products that are in their highest vibrational state. A vibrationally inverted population is a prerequisite of stimulated emission of radiation.

Description

1 2069

SURFACE CATALYST INFRA RED LASER

TECHNICAL FIELD OF THE INVENTION

The présent invention relates generally to solid-state devices for converting or extracting energy fromhydrocarbon-oxidizer reactions. More specifically, thisinvention relates to a significant improvement of theprocess for the efficient conversion and extraction ofenergy in the form of optical émissions and of cohérentradiation and from reactants such as hydrocarbons,hydrogen or other combustible materials reacting on acatalyst surface with air or other oxidizers.

BACKGROUND OF THE INVENTION

One method to convert Chemical reactant energydirectly into useful work such as electricity useselectrochemical couples such as batteries- and fuelcells. In this method, a substantial fraction of thereactant bond energies may be converted directly intoelectrical potential. However, the physical chemistryunderlying these processes limits the rate of suchconversion substantially. The resuit is a power permass and power per volume that is orders of magnitudesmaller than that of a mechanical engine.

Another method uses gas dynamic processes toconvert Chemical energy directly into a dynamic Stateexhibiting a population inversion. The energy isextracted from this System as cohérent radiation.However, the reactants and exhausts of this method areusually dangerous and incompatible with human safetyconsidérations. Moreover, these devices cannot beefficiently miniaturized.

Therefore, it is highly désirable to hâve a simplermethod and System for extracting efficiently without 1 1 2069 having to use harmful products and without producinghazardous byproducts in the process. A recent research suggests that certain simple,energetic atoms reacting on a catalytic surface produceproducts exhibiting a population inversion. An invertedpopulation is the prerequisite for stimulated émissionof radiation, which is one method to remove the energyfrom the reaction and to retain its high degree ofusefulness.

One problem in the prior State of technology is theprocess of creating highly energetic species on thecatalyst surface, such as hot atoms and mono-atomicoxygen, that 1) retain a significant amount of theChemical energy for reactions, instead of dissipating itas a heat of adsorption, and 2) that will produce aninverted population as a product of the reaction. Theissue in the création of hot atoms, such as mono-atomicoxygen, is that it usually takes more electrical energyto produce the hot atoms than can be extracted from theresulting Chemical reactions.

Research has suggested that mono-atomic, energeticspecie reacting with simple adsorbed specie may formvibrationally inverted products, and that this inversionmay occur in many Systems. For example, research hasshown that when gas phase oxygen atoms react withdeuterium adsorbed on a tungsten surface, OD radicalsare formed in the inverted State, with the highestpopulation appearing at vibrâtional level 6. Thisrepresents a substantial fraction of the availablereaction energy being concentrated in the invertedState. Shin, HK, "Vibrationally Excited OD Radicals FromThe Reaction Of Oxygen-Atoms With Chemisorbed DeuteriumOn Tungsten," Journal Of Physical Chemistry A, v.102{#13), pp. 2372-2380, MAR 26, 1998.

Similar research showed that gas phase atomicoxygen reacting with adsorbed hydrogen on the surfaceproduces population inverted, OH radicals within 100femtoseconds. Ree J, Kim YH, Shin HK, "Dynamics Of Gas- 2 1 2069

Surface Interactions: Reaction Of Atomic Oxygen WithChemisorbed Hydrogen On Tungsten, " Journal Of PhysicalChemistry A, V. 101 (#25), pp. 4523-4534, JUN19, 1997. 5 It was shown in Kim, M. S. and J. Ree, "Reaction of Gas-Phase Atomic Hydrogen with Chemisorbed HydrogenAtoms on an Iron Surface," Bulletin of the KoreanChemical Society, Volume 18, Number 9 (1997), COMMUNICATIONS, pp 985-994, that gas phase atomic10 hydrogen reacts with chemisorbed hydrogen on an iron surface to form population inverted, desorbed diatomichydrogen molécules.

It is known that when atomic oxygen in the gasphase reacts with carbon monoxide adsorbed on a platinum 15 catalyst surface, the fraction of reactive collisionsproducing molécules having vibrational energiescorresponding to levels v3 = 9 to 13 is found to be veryhigh and'exhibits a vibrational population inversion.Ree, J. ; Y. H. Kim, and H. K. Shin, "Reaction of atomic 20 oxygen with adsorbed carbon monoxide on a platinumsurface," Journal of Chemical Physics, January 8, 1996, Volume 104, Issue 2, pp. 742-757. This would beuseful except for the fact that the mono-atomic oxygenatoms for this reaction must be created using 25 inefficient means, namely electric arcs.

Yet another research has shown that mono-atomic oxygen atoms can be created directly on a catalyticsurface by irradiation with UV light. The most probableresuit of such irradiation is the production of mono- 30 atomic oxygen atoms. The next most probable resuit isdesorption. The issue with this approach is the lowefficiency of the génération and conversion of UV lightinto dissociâted oxygen atoms. Tripa, C. Emil,Christopher R. Arumaninayagam, John T. Yates, Jr., 35 "Kinetics measurements of CO photo-oxidation on

Pt (111)," Journal of Chemical Physics, July 22, 1996,Volume 105, Issue 4, pp. 1691-1696. 3 1 2069 A related research has also shown that oxygenmolécules preferentially adsorb on the step sites of acatalyst such as platinum, and that photo generatedmono-atomic oxygen atoms preferentially react with otherradicals or molécules also adsorbed on the step sites.Atomic and molecular species generated by the photolysisof aligned molécules adsorbed on crystalline solids tendto move preferentially in particular directions relativeto the crystal surface. For example, photo-generatedmono-atomic oxygen reacts preferentially with adsorbedCO to make excited State CO2. The feature here is theefficiency of reaction of the hot atoms with othersurface reactants. An issue here is the preferentialproduction of hot atoms. Tripa, C. Emil; John T. YatesJr, "Surface-aligned reaction of photo generatedoxygen atoms with carbon monoxide targets," Nature, Vol398, pages 591 - 593 (1999) , 15 April 1999.

Another research showed that the UV photons createhot électrons on a catalyst métal surface and whichinteract strongly with adsorbed oxygen to cause thetrapped oxygen atoms to dissociate or desorb. Thesalient point is that adsorbates trap in metastableStates before they dissociate, and that hot électronscan stimulate such States efficiently. Experimentsshowed that gas phase oxygen molécules adsorb first as asuperoxo-like specie (molécule singly charged onsurface) and are then trapped in a shallow barrier oforder 0.1 eV. Then the molécule may overcome thebarrier and become a peroxo-like specie (doubly charged)in a barrier of order 0.5 eV. Finally, the molécule mayovercome this barrier and dissociate into hot atoms. Theexistence of precursor phases is apparently fairlycommon and observed in various forms of platinum,palladium and iridium catalysts. Nolan, P. D. ; B. R.Lutz, P. L. Tanaka, J. E. Davis, and C. B. Mullins,"Eolecularly chemisorbed intermediates to oxygenadsorption on Pt ( 111 ) : A molecular beam and électron energy-loss spectroscopy study," Journal Of Chemical 4 1 2069

Physics Volume 111, Number 8, 22 August 1999. Nolan PD,Lutz BR, Tanaka PL, Mullins CB, "Direct vérification ofa high-translational-energy molecular precursor tooxygen dissociation on Pd(lll)," Surface Science v.419(#1) pp. L107-L113, DEC 24, 1998. Nolan, P. D.; B. R. Lutz, P. L. Tanaka, J. E. Davis, and C. B. Mullins,"Translational Energy Sélection of Molecular Precursorsto Oxygen Adsorption on Pt(111)," Physical ReviewLetters , VOLUME 81, NUMBER 15 12 OCTOBER 1998. Davis, J. E. ; P. D. Nolan, S. G. Karseboom, and C. B.Mullins, "Kinetics and dynamics of the dissociativechemisorption of oxygen on Ir(lll)," J. Chem. Phys. 107 (3), 15 July 1997, pp943, 10 pages.

Inverted products can be formed by associativedesorption. Expérimente hâve shown that nitrogenmolécules formed upon catalytic décomposition of ammonia(cracking) over Ru may show a vibrational populationinversion. The associative reaction begins with theatomic séparation of the nitrogen atoms being similar tothat of the surface catalyst atoms and just slightlygreater than that of the ground State of a productnitrogen molécule. Murphy, M. J. ; J. F. Skelly, andA. Hodgson; B. Hammer, "Inverted vibrationaldistributions from N2 recombination at Ru (001) : Evidencefor a metastable molecular chemisorption well," Journalof Chemical Physics -- April 8, 1999 -- Volume 110,

Issue 14, pp. 6954-6962.

That reaction rates can be stimulated and increasedby many orders of magnitude with picosecond duration andtiming is illustrated by recent experiments depicted ina technical publication. Bonn, M. ; S. Funk, Ch. Hess,D. N. Denzler,C. Stampfl, M. Scheffler, M. Wolf, G.

Ertl, "Phonon- Versus Electron-Mediated Desorption andOxidation of CO on Ru(0001)," Science, Volume 285,

Number 5430 Issue of 13 Aug 1999, pp. 1042 - 1045.

The stretched molécule represents the initialcondition where the atomic séparation during thevibrational oscillation starts with the association 5 1 2069 reaction at. the extrema, defining a reaction product inthe highest excited State. It is noted "Vibrational"modes also include the vibration of any specie on thesurface against that surface.

Simple reactant radicale on the catalyst surfacemay preferentially form in mechanically simple ways,which often strongly favor a single vibrational mode forthe energy to concentrate, again favoring an invertedpopulation. Furthermore, mono-atomic oxygen atomssupplied externally to the catalytic surface may cause apopulation inversion in the products of carbon monoxidereaction to carbon dioxide and in the surface catalyzedoxidation of hydrogen.

Heretofore, the oxygen adsorption process wastedapproximately half the reaction energy as heat on thecatalyst surface. Therefore, a new method to conservesuch energy and extract it into useful energy is highlydesired.

SUMMARY OF THE INVENTION

The présent invention is directed to a method andSystem for using a catalyst and reactants to create the"simple, energetic atoms" needed for the génération ofthe inverted population. In one embodiment, the présentinvention captures the reaction energy based on theprinciple that some energetic atoms reacting on acatalytic surface produce products exhibiting apopulation inversion.

This invention créâtes population inverted reactionproducts from fuel and oxidizer reactions on a catalystsurface. A laser operating on the inverted populationwould efficiently extract the energy from the System.

One embodiment uses the hot atom produced duringdissociative adsorption of oxygen on catalyst surfacesto provide energetic oxygen free radicals on thosesurfaces and to cause direct and prompt reaction with afuel specie, also on the catalyst surface, which biases 6 1 2 069 reactions towards formation of population invertedproducts. Examples of fuel specie include, but are notlimited to, hydrogen, a hydroxyl, a carbon monoxide or ahydrocarbon fragment.

Another embodiment of this invention créâtes apopulation inversion by biasing the reaction by choiceof catalyst species to form product molécules that arestretched at the moment of desorption from the catalystsurface. Another embodiment créâtes the populationinversion by biasing the reactants by choice of catalystto cause simple reactants with a large fraction of theirenergy available upon associative desorption. Anotherembodiment uses a solid-State method to provide hotélectrons directly, and without the use of UV light,which in turn stimulâtes dissociation of the precursor,peroxo- chemisorbed oxidizer, and cause an avalanche ofsurface reactions.

In one embodiment, the présent invention uses alaser to extract the energy from an inverted population,resulting in conversion of a substantial fraction, andin some cases a majority, of the Chemical reactionenergy into one or several, nearly monochromatic,cohérent bearas of light. Such a beam retains the highquality of the energy and is most useful because it canbe efficiently converted into electricity, for example,by passing a monochromatic beam into a photovoltaic cellwith band gap slightly smaller than the beam photonenergy, and equally efficiently into mechanical forcesthrough other means.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the présent invention willnow be described, by way of example only, with referenceto the accompanying drawings in which:

Figure 1 shows a schematic cross section of anapparatus for energy génération using separatedreactants in one embodiment of the présent invention; 7 1 2069

Figure 2 illustrâtes a cross section of anapparatus in one embodiment of the présent invention forgénérâting energy using free flowing, mixed reactantsfor forming inverted excited State products; and

Figure 3 illustrâtes a cross section of anapparatus in one embodiment for générâting power byexternally stimulating and triggering reactions.

DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENT OF THE INVENTION

The présent invention is directed to biasing thereactions occurring on the surface of a catalyst towardthose that deliver a substantial fraction of the energyinto product species that exhibit, as a resuit of themethods of this invention, a population inversion.

Stretched molécules associated with adsorption anddesorbtion hâve closely related, réversible effects,both related to population inversion. A method of theprésent invention in one embodiment uses the hot atomscreated upon dissociative chemisorption reacting with afuel-rich catalyst surface; in another embodiment, amethod in the présent invention uses stretched moléculesproduced during associative desorbtion from a catalystsurface; in yet another embodiment, the method of theprésent invention uses excited State simple productseither desorbing from catalyst surfaces or vibrating onthose surfaces for a usefully long time; ail methodsbeing capable of producing reaction products withpopulation inversions.

According to one embodiment of this invention acatalyst surface is flooded with fuel, such as éthanol,methanol, alchohols or gaseous products of a hydrocarbonreformer. The products of hydrocarbon reformer mayinclude, but are not limited to, CO and H2. A catalystis chosen such that ail or nearly ail the reactantsadsorb on the catalyst surface. Many catalysts satisfythese criteria, especially the platinum group catalysts. 8 1 2 069

The fuels chemisorb and dissociate into simple radicalson the catalyst surface, such as a platinum catalyst.Under favorable conditions, such as when the catalystsurface is cooled or when the mixture is fuel-rich, theadsorbed fuel molécules will occupy most of the surfacesites and leave relatively few sites for oxygenadsorption. The oxygen, upon adsorption under theseconditions, dissociâtes via a process where it isobserved that nearly the entire dissociation energy isshared equally between two, mono-atomic oxygen atoms, orfree radicals, each moving away from the dissociationsite with approximately 1 électron volt ("eV") ofenergy, that is, with nearly ail the chemisorptiondissociation energy. These free radicals with 1 eV ofkinetic energy are referred to as "hot atoms."

In the présent invention, such hot atoms almostexclusively find adsorbed fuel radicals as the first,nearest and next nearest collision partners, because thecatalyst surface is flooded with fuel. Accordingly, thehot atom free radical places non-thermal energy directlyinto the Chemical reaction coordinate and promptlyreacts with the collision partner, as a resuit of havingapproximately 1 eV of energy, which is approximatelytwice the measured activation energy (typically 0.5 eV)needed to initiate the reaction, and forms reactionproducts that are by necessity born in their highestexcited vibrational state.

According to the présent invention, a hot atomformed from the dissociation process is made to reactbefore it can reach equilibrium on the catalyst surfaceand thereby does not dissipate the energy as heat to thesubstrate or catalyst lattice but instead makes nearlyail of the energy of adsorption available for populationinversion.

In one embodiment of the présent invention, the useof a surface with approximately a monolayer or greatercoverage of fuel reactant also reduces the adsorptionenergy of the oxygen adsorbed species, which adsorption 9 ? 06 9 heat would otherwise become unavailable to reactionproducts.

The présent invention is also directed toextracting the energy from the multiple quantum levelsassociated with the vibrational energy of newly formedproduct species, whether or not the specie remainsadsorbed on the surface of the catalyst. The multiplequantum transitions are ail dipole active for specie ona surface.

In one embodiment of the présent invention, anoptical System, for example, a laser, causes stimulatedémission of radiation to occur between the highlypopulated, higher vibrational quantum number energylevels and the sparsely populated, lower quantum numberlevels, and thereby removes a substantial fraction ofthe energy in the form of cohérent radiation.

In one embodiment, a photovoltaic device maytransform the radiation emitted due to the populationinversion directly into electricity, with or without theuse of lasers.

The laser may use overtone transitions betweenlevels, resulting in multiples, e.g., double, triple orhigher, of the transition frequencies usually associatedwith single level transitions.

This can be accomplished by the use of an opticalcavity tuned to an overtone transition, for example,spanning 2, 3 or more vibrational transitions of theexcited State reaction product, and optically enclosingthe surface reaction zone. The excited State productsare typically hydroxyl, a water molécule, a CarbonMonoxide, or carbon dioxide specie.

Another way to accomplish this is to use sequentiallaser stimulation puises of different frequencies tocontrol and sequence the transitions of the invertedproduct specie. The radiation is amplified each time itpasses through the inverted medium. Such a sequence ofinput radiation sequentially depopulates selected 10 1 2069 inverted levels of the multi-level vibrational energylevels of the inverted products.

The State of the art of making laser cavitiespermits geometries that are favorable to havingreactants and chambers within optical résonance région.One way to do this is to form a laser cavity from aphotonic band gap cylinder cavity, wherein the cavity isformed by confinement of light within a hollow core (alarge air hole) in a silica-air photonic crystal fiber.

In one embodiment of the présent invention, the useof overtone transitions magnifies the frequency orenergy différence between upper level transitions andlower level transitions and hence allows this inventionto select such transitions and to sequence theirstimulation and émission. That is, the stimulatedémission may be stimulated first between the highestlevels, then between medium levels and on down to lowerlevels, in sequence. The anharmonic nature of thepotential well associated with the multi-leveltransitions of the Chemical reaction products causesenergy level spacing of upper level transitions tobecome doser compared to lower level transitions as theenergy level approaches the top of the potential well,which permits différentiation and sélection of desiredtransitions.

In one embodiment, use of the strong electricfields found at the catalyst surface breaks thesymmetry, induces molecular polarization and causesotherwise forbidden molecular transitions such asmultiple overtone transitions of adsorbed, vibrationallyexcited products, to exhibit strong dipole transitionmatrix éléments. This in turn permits multi-quantumtransitions and renders these transitions to be activecandidates for stimulated émission.

The présent invention also provides a way to insertthe reacting species on to the surface so that theinfrared absorptions of the reactants absorb the least 11 12069 possible fraction of the desired émissions, resulting in a net increase in the efficiency of the System.

In one embodiment, the fuel species, known forbroadband long wavelength infra red absorbtions, may beinserted from a porous substrate, from within tubes,and/or from channels that reflect IR radiation at thelaser frequencies, and where such tubes may hâve micro-meter or nano-meter holes drilled into them to permitfluid flow, and where such tubes or channels may hâvecatalyst clusters or layers placed on their surfaces.

One such a System is a wicking fuel delivery System.

This System would include a fuel bed, which can be awetted material such as métal wool or fibers wetted byfuel or a channel of fuel, and a porous substrate whosesurface includes catalyst or catalyst clusters. Theporous substrate is in contact with the wicking system.The substrate may be a zeolite, an aerogell, or anaerogell or other suitable substrate permeated withholes such as may be drilled with a laser.

In one embodiment, the use of overtone radiationmay place the prédominant frequency of the cavity out ofrange and significantly above the spectral régionsassociated with intense IR absorption.

The présent invention is also directed to causingadsorbed molecular species in excited States to extendthe vibrational lifetimes of the product specie so thatthe vibration energy is minimally dissipated into thelattice during the energy extraction process.

In one embodiment, the substrate upon which thecatalyst clusters résidé may be a non-conductor, whereinusing the non-conductor has been shown to increase thelifetime of certain vibrating specie by orders ofmagnitude over that of the same species on a conductingsubstrate.

In one embodiment, the substrate may be chosen sothat the vibration frequencies of the substrate mismatchthose of the catalyst. This isolâtes and découplés thesuperlattice vibrations from the substrate vibrations. 12 i 2 069

This increases the lifetime of a product in an excitedState on that surface. Such material may include, forexample, Chemical vapor deposited diamond, with veryhigh relative phonon frequencies, or in another examplelead, with very low phonon frequencies.

The présent invention is also directed to causingreaction avalanches, which in turn may be used to causehigh peak power puises of cohérent radiation. In oneembodiment of the présent invention, specie such as theperoxo precursor adsorbed oxygen molécules are stimulated to dissociate upon electrical command usinghot électrons generated by a solid state forward biaseddiode. In such a diode, the catalyst is the métalelectrode and diode element of a métal-semiconductor,Schottky diode. When the métal element has a thicknessless than a few times the energy raean free path ofélectrons in that diode, those électrons injected intothe métal due to a forward bias are formed as hotélectrons with energy at least the same order ofmagnitude as the sum of the forward bias and theSchottky barrier height.

These intermediate peroxo species hâve anactivation barrier against dissociation of order 0.3électron volts. Typical dissociative adsorptionactivation barrière for such trapping mediatedadsorbates are of order 0.1 to 0.6 électron volts. Thetypical Schottky barrier of a diode formed between themetals platinum, palladium, tungsten, copper, silver andgold and a semiconductor such as Silicon are typicallyof order 0.5 volts. A forward bias of 0.5 volts wouldflood the surface of the catalyst and its adsorbateswith 1 eV hot électrons.

In one embodiment of the présent invention,limiting the stimulation électron energy not only causesa triggering of the transition of the adsorbate precursor States to dissociation but also biases thetriggering so the transition does not go backwards,towards desorption. If the adsorbate does go backwards, 13 i2069 limiting the stimulation électron energy increases thefraction that go the desired direction. The appropriatevalue for the stimulation energy is a value less thanthe energy of the dissociation barrier. A good choice ofenergy is also above that of the barrier to the Statejust before dissociation. For example, for peroxo Stateoxygen on platinum, the barriers hâve a différence oforder 0.2 eV. The idéal hot électrons produced by ourinvention would hâve an energy spread less than thisdifférence, for example of 0.2 eV, and an absolute valuewithin the reactivity range for the adsorbed State, forexample, of order 0.1 to 1 eV.

Another method to bias the absorbtions of radiationfavoring the dissociation path is to enhance thevibration levels of that specie, such as a peroxo-chemisorbed specie. To do this, the présent inventionmay use an optical cavity to enhance that radiation.

For example, peroxo-chemisorbed oxygen on platinum has a690 per centimeter (infra red optical) résonance. Anoptical source of such radiation, such as produced by anelectrical discharge or by a diode laser, wouldselectively stimulate this résonance.

Yet another method may provide such opticalradiation in a manner that can be sequenced both infrequency and in time. A chirped laser is a method todo this. Some of the radiation that is produced by themethod and apparatus of this invention may be tailoredto be this desired radiation.

According to the présent invention, other specie onthe catalyst surface, such as fuel molécules or radicalsmay be used as hot électron absorbers. As such, theywould dissociate into radicals themselves or transferenergy to the peroxo- and superoxo- chemisorbed oxygenprecursors, to stimulate the reaction avalanche.

In one embodiment, when control over the timing ofreaction initiation is desired, the catalyst may bechosen to hâve a charged precursor with higher 14 1 2 069 activation barriers against dissociation, a conditionwhich normally makes a catalyst less active.

In one embodiment, the power conversion device ofthe présent invention using hot atoms may include: substrate(s) such as the catalyst itself, silica,alumina, titania, semiconductor, or convenient materialson which a catalyst, such as platinum nanoclusters, isplaced; a means of flooding the catalyst surface with fuel,such as a porous substrate fed with liquid fuel, a mechanism of bringing air as the oxidizer intothe chamber, such as a channel permitting air input andreaction product exhaust to flow over the catalystsurface ; hydrocarbon reactant fuel, such as liquid éthanol,methanol, higher alchohols, or the product ofhydrocarbon reformers, such as mixtures containinghydrogen and carbon monoxide; a poly-chromatic, résonant optical cavity enclosingthe catalyst surface reaction région; and a laser System using the optical cavity to extractcohérent radiation from the inverted population ofreaction products.

According to one embodiment, the hot atoms produceassociated reactants born in their highest vibrationalStates, obviating the need to supply such monatomicspecie externally.

In some reactant-oxidizer-catalyst cases thereactants, such as hydroxyl radicals, desorbimmediately, which places them in a long-lived State(approximately 200 picoseconds between collisions withother gas molécules, and lifetimes of 10 to 100collisions) compared to lifetimes on the catalyst métalsurface (1 to several picoseconds). The laser System inthis case stimulâtes transitions to remove thevibrational energy. The hydroxyl will not find manyother hydroxyls with which to resonantly exchangeenergy, thereby precluding rapid thermalization via 15

I

1 208 résonant collisional exchange of the raolecular vibrational excitations.

In other cases the products, typicallyvibrationally excited OH or CO, may remain on thecatalyst surface, and in this case the lifetime of thevibrations would be of order picoseconds. In this casethe catalytic surface electric field causes multiquantumtransitions to become more strongly dipole active, andthe laser System may now induce transitions on thesecond, third or 4th overtone, for example of theexcited State OH or CO. With turnover numbers of order10,000 per site per second, typical of good catalystsopérâting in their desired operating conditions, a 100layer per centimeter {"cm") reaction chamber would yield100 watts per cubic centimeter of inverted population.This permits stimulated émission under conditions thatwould otherwise be too difficult.

Figure 1 schematically shows a cross section of adevice to implement some of these concepts. In Figure1, a substrate 101 on which a catalyst 102 is affixed,where a gas flow channel 103 guides air 104 over thecatalyst 102. The catalyst substrate 101 is porous andpermits the flow of fuel 105 from the fuel side of thesubstrate 101, which liquid or gaseous fuel is guided tothe substrate 101 by the fuel channel 106. A polychromatic résonant optical cavity, formed by lasermirror 107 and laser output mirror 108, a laser controlSystem 109, and the greater optical cavity 110, enclosethe région of catalytic surface reactions 110 andextract energy in the form of cohérent light 111.

Exhaust 112 leaves the System and flows through the exitchannel 113. Structural materials 114 support theseéléments and form the fuel, air and exhaust channels.

In another embodiment, the présent invention usesstretched molécule associative desorbtion or excitedstate products desorbing from catalyst surfaces. Inthis embodiment, a power conversion device may include: 16 1 2 069 substrate (s) such as the catalyst itself, silica,alumina, titania, a semiconductor or well chosenmaterials on which a similarly well chosen catalyst isplaced; a mechanism for bringing fuel and air (theoxidizer), into the chamber, such as a channelpermitting reactant input and reaction product exhaustto flow over the catalyst surface; liquid éthanol, methanol , higher alchohols, or theproduct of hydrocarbon reformers, such as mixturescontaining hydrogen and carbon monoxide, as thehydrocarbon reactant fuel; a poly-chromatic, résonant optical cavity enclosingthe catalyst surface reaction région; and a laser System using the optical cavity to extractcohérent radiation from the inverted population ofreaction products.

According to this embodiment, combinations ofreactant and catalyst, which hâve been chosen to favorproduction of inverted products, are caused to flowinto the reaction chamber containing the catalystsurfaces and where the optically enclosing résonantcavity and its associated laser System extracts asignificant fraction of the product reaction energy asradiation. The products are then exhausted and removedfrom the optically enclosed System, which removes groundState species and maintains the population inversion.

One way to achieve this has the optical cavityenclosing only a région close to the catalyst surface,that is, to use a surface laser, while permitting gasflow out of the surface région. The State of the art ofsurface lasers, such as dise lasers and single modephotonic band gap Systems permits such cylindersymmetry, air hole Systems.

Also, catalysts may be chosen according to themethod wherein the catalyst exhibits a "pressure gap,"as it is referred to in the technical literature. As isthe case with CO oxidation on Ruthénium, the oxygen rich 17 1 2069 adsorption lowers the oxygen heat of adsorption, permitting the desired oxidation and making Ru one ofthe most active catalysts, whereas the characterizationsperformed under ultra high vacuum conditions show Ru tobe one of the least catalytic.

In this embodiment, one may tailor the propertiesof the desired catalyst. It has been observed thatotherwise catalytically inactive metals, such as gold,are caused to become reactive, and relatively goodcatalysts, as the number of underlying métal layers isdecreased, down to 1 and 2 monolayers, for example.

At 6 or more monolayers, the affinity of gold fordissociation of oxygen has been observed to benegligible. As the number of monolayers decreases to 3or 2, the affinity is sufficient to dissociate oxygen,but not to bind it too strongly to the gold métal,making the 2 monolayer catalyst efficient. At 1monolayer the affinity of the gold substrate catalystfor oxygen is so strong that the oxygen becomesunavailable for reaction.

In one method to choose catalysts of the présentinvention, a method of tailoring and choosing thecatalyst favoring a stretched molécule may include: creating a list of catalyst candidates from theentire set of metals; choosing the catalyst metals with the interatomicspacing of catalyst atoms such that the reaction productexit channel would form a product with a stretched bond; forming a catalyst cluster including atomicmonolayers in a cluster of nanometers dimension on anoxide substrate; choosing the number of monolayers to control theaffinity for both oxygen and fuel.

For example, choose a gold catalyst of 2 monolayersthickness placed on titania to favor carbon monoxideoxidation.

Figure 2 shows a cross section of an apparatus toimplement sonie of these concepts. Figure 2 shows a 18 1 2069 substrate 201 resting on a support 202 and on which acatalyst 203 is affixed, causes fuel 204 and air 205entering from the input channel 206 to react, excitedState products to be formed and radiate in the reactionchannel 207, and causes exhaust 208 to leave via theexhaust channel 209. A polychromatic résonant opticalcavity, formed by laser mirror 210 and laser outputmirror 211, a laser control System 212, and the greateroptical cavity and reaction zone 207, enclose the régionof catalytic surface reactions and extract energy in theform of cohérent light 213.

In another embodiment, the présent inventionfavoring the stimulation and timing of reactionavalanches may include: a chamber similar to the one used in the previousembodiment; a semiconductor substrate and catalyst forming aSchottky diode, with catalyst thickness less than orapproximately equal to a few times the energy mean freepath of électrons in the métal; a mechanism providing a pulsed forward bias on thediode.

In one embodiment, a short-pulse light source suchas a laser may also be used to provide the hot électronsto energize the trapped adsorbate. For example, such alight source will cause a chemisorbed peroxo-like doublycharged oxygen molecular specie on a platinum catalystto accelerate its transition over the approximately 0.29eV barrier, where the molecular specie preferentiallymoves so as to dissociate. This favors dissociationbecause the reverse reaction, création of the super-oxo-like, singly charged molecular oxygen, has a higheractivation barrier energy, and the physi-sorbed speciehas an even higher activation barrier. The laser mayprovide the fastest and shortest puises. Alternativelya hot électron injector diode may be used.

According to one embodiment, pulsing the diode with0.5 to 1 volt for short times, such as fractions of a 19 1 2069 picosecond, raises the energy of a large fraction of thedoubly charged molecular oxygen to the level needed todissociate.

The hot électrons created upon such instantaneousheating of a métal on a thermal insulating substrate maybe used in a régénérâtive feedback mode to furtherstimulate the peroxo-like specie. In this way, a verysmall amount of initial stimulator energy may be needed,compared to the energy output of the System.

Figure 3 shows a cross section of an apparatus toimplement some of these concepts. Figure 3 showsreactions on the catalyst surface are stimulated tooccur in puises, concentrâting the subséquent radiatedenergy in a small time. A fuel 301 and air 302 mixtureenter the reaction zone through the input channel 303and contact the catalyst surface 304 and physisorb,chemisorb or adsorb. The catalyst 304 and thesemiconductor substrate 305 form a Schottky diode. Thethickness of the catalyst 304 is of order 1 to 5nanometers, which is less than the mean free path ofélectrons in preferred catalysts such as platinum,palladium, tungsten, rhodium, ruthénium, copper, silveror gold. A short electrical puise with positive on thecatalyst electrode 306 and négative on the semiconductorohmic contact 307 causes a forward bias and a forwardcurrent in the diode formed by the catalyst - semiconductor element. The électrons of this forwardcurrent hâve an excess energy approximately equal to andin excess of the forward bias voltage, and these floodthe catalyst surface, initiating a Chemical reactionavalanche. The hot électrons cause adsorbed, chemisorbedmolecular species trapped in precursor States tosurmount their activation barriers and adsorb as atomicspecie on the catalyst surface.

The electrical trigger puise causes the reactantsto react ail at once and together, causing orders ofmagnitude increase in the concentration of products, 20 1 2069 such as excited State specie radiating in the reactionchannel 308. Exhaust 309 leaves via the exhaust channel310. A laser formed by laser mirror 311 and laser output5 mirror 312, a laser control System 313, and the greater optical cavity and reaction zone 308, enclose the régionof catalytic surface reactions and extract energy in theform of cohérent light 314.

While the invention has been particularly shown and 10 described with respect to a preferred embodiment thereof, it will be understood by those skilled in theart that the foregoing and other changes in form anddetails may be made therein without departing from thespirit and scope of the invention. For example, those 15 skilled in the art will appreciate that the features ofthe invention may sometimes be used to advantage withouta corresponding use of the other features shown ordescribed herein above. Similarly, some features may becombined, within the scope and équivalents of the 20 présent invention, to achieve a desired resuit. 21

Claims (50)

1 2069 CLAIMS We claim:

1. A method for creating hot atoms as a source ofenergetic free radicals on a catalyst surfacecomprising: adsorbing a molécule on a catalyst via a precursormediated trapping; flooding a surface of the catalyst with one or morereactant molécules.

2. The method of claim 1, wherein the adsorbingincludes: adsorbing an oxygen molécule; and trapping the oxygen molécule on one of platinum andsilver.

3. The method of claim 1, the method furtherincluding: cooling the catalyst to induce condensation andconcentration on the catalyst surface.

4. The method of claim 1, wherein the floodingincludes: flooding the catalyst surface with fuel to cause abias of the dissociative chemisorption process towardthe création of hot atom oxygen free radicals, wherein acollision partner of the hot atom is the fuel.

5. The method of claim 1, wherein the methodfurther includes: selecting a catalyst such that the oxidizerchemisorption, dissociation, and physisorption energy isa fraction of the available Chemical bond energy; and the flooding includes flooding the catalyst surfacewith oxidizer radicals to cause a bias of thedissociative chemisorption process toward a création of 22 1 2069 hot atom fuel free radicale, wherein a collision partnerof the hot atom is the fuel specie.

6. The method of claim 1, wherein the hot atom-containing molécule is fuel.

7. The method of claim 6, further including:selecting the catalyst as one or a combination of platinum, palladium, iridium, Rhénium, Rhodium.

8. The method of claim 6, further including:selecting the reactant specie as one or combination of methanol, éthanol, and a product of hydrocarbonreformers.

9. A method of stimulating oxidizer Chemicalreactions comprising: forming a catalyst surface using a catalystfavoring accumulation of a charged chemisorbed precursoron the catalyst surface, the precursor having anactivation barrier to dissociative adsorption less thanthe activation barrier to revert to its own precursorState; and causing the charged chemisorbed precursor toacquire sufficient energy to surmount the dissociationbarrier.

10. The method of claim 9, wherein the precursorincludes a peroxo-like doubly charged oxygen precursor.

11. The method of claim 9, wherein the precursorincludes one of singly charged super-oxo and physisorbedState.

12. The method of claim 9, wherein the catalystincludes one or combination of platinum, palladium,iridium, Rhénium, and Rhodium. 23 1 2069

13. The method of claim 9, further including:inducing transitions in energy well of the charged precursor with a laser having a predetermined photonenergy.

14. The method of claim 9, further including:emitting optical radiation, including infra redoptical radiation, using an electrically drivenlight source for causing the charged precursor toacquire sufficient energy.

15. The method of claim 14, wherein the lightsource includes a gas discharge producing opticalradiation.

16. The method of claim 9, further including:stimulating a precursor dissociation using an electric field provided by field émission électrodeswithin nanometer proximity of the catalyst surface.

17. The method of claim 9, further including:forming a catalyst layer; forming a substrate including a diode in contactwith the catalyst layer, wherein the thickness of the catalyst layer is suchthat a distance from an adsorbate on the catalystsurface to the substrate is less than 3 times the energyfree path of an électron near the Fermi level; and applying a puise of electrical energy to forwardbias the diode.

18. The method of claim 17, wherein the substrate has a heat conductivity at least 10times lower than that of the catalyst.

19. The method of claim 18, wherein the substrateincludes thin oxide layers to control diode junctionbarrier heights. 24 12 069

20. The method of claim 19, wherein the oxidelayers hâve a thickness of 100 nanometers or less.

21. The method of claim 9, further including:stimulating the charged precursor by one of a pulsed light source, a pulsed laser, and pulsed electricfield.

22. The method of claim 21, wherein thestimulating is performed for a duration less than 20nanoseconds.

23. The method of claim 22, wherein the operatingtempérature during the stimulating is less than 300Kelvin.

24. The method of claim 15, further including:removing heat from the substrate.

25. The method of claim 15, further includingapplying one or combination of fuel and air in a reaction channel to remove heat from the substrate.

26. The method of claim 15, wherein the puise ofelectrical energy includes a pulsed forward biassufficient to émit hot électrons into an electrodesurface of the diode.

27. The method of claim 26, wherein the pulsedforward bias is greater than 0.1 électron volts ("eV").

28. The method of claim 9, wherein one or more hotélectrons having a predetermined energy are used tocause the charged precursor to acquire energy.

29. The method of claim 28, wherein thepredetermined energy is less than 1 eV. 25 1 2 069

30. The method of claim 15, wherein an electrodeof the diode is constructed using the same material asthe catalyst.

31. The method of claim 15, wherein the durationof the puise is shorter than the duration of reactionsoccurring on the catalyst surface.

32. The method of claim 31, wherein the durationof the puise is 0.1 picoseconde.

33. An apparatus to generate hot atoms,comprising: a porous substrate; a catalyst placed on the substrate for allowingreactions to occur on a surface of the catalyst; and a laser System surrounding the surface of thecatalyst and forming an optical cavity in the région ofcatalytic surface reaction.

34. The apparatus of claim 33, wherein thecatalyst is one of Platinum, Iridium, Rhodium,Ruthénium, Palladium, Tungsten and a transition métal.

35. The apparatus of claim 33, wherein thecatalyst includes a monolayer nanocluster on an oxidesubstrate.

36. The apparatus of claim 35, wherein themonolayer nanocluster includes any one of gold ontitania, and a métal on an oxide.

37. The apparatus of claim 33, wherein thecatalyst includes catalyst islands of gold on titaniumoxides. 26 1 2069

38. The apparatus of claim 33, wherein the poroussubstrate includes one of zeolite and aerogell.

39. The apparatus of claim 33, wherein the poroussubstrate includes a dielectric reflector.

40. The apparatus of claira 39, wherein one or morenano-islands of catalyst are deposited with équivalentthickness less than a pénétration depth of the laserradiation.

41. The apparatus of claim 40, wherein inter-island spacing of the one or more nano-islands ofcatalyst is at least several atomic dimensions.

42. The apparatus of claim 41, wherein catalystisland dimensions are at least less than a quarterwavelength of the overtone radiation.

43. The apparatus of claim 33, wherein the poroussubstrate includes a non-conducting substrate favoringfuel adsorption, and the catalyst includes one or morenanometer dimension catalyst islands favoring oxygenadsorption, wherein a product of a reaction occurring on thecatalyst résidé on a non-conductor when the productmigrâtes and diffuses.

44. The apparatus of claim 43, wherein the non-conducting substrate includes one of aluminum oxide,Silicon oxide, titanium oxide, and ionic salts.

45. The apparatus of claim 33, wherein thesubstrate is a non-conducting ionic solid.

46. The apparatus of claim 33, wherein the opticalcavity further includes a dichroic resonator. 27 1 2069

47. The apparatus of claim 33, wherein theapparatus further includes: a first wall surrounding the catalyst surfaceforming a first channel between the catalytic surfaceand the first wall, the région of catalytic surfacereaction being exposed to the first channel, wherein reactants enter the région via the firstchannel.

48. The apparatus of claim 33, wherein exhaustsfrom the reaction leave the région via the firstchannel.

49. The apparatus of claim 33, wherein theapparatus further includes: a second wall surrounding a bottom side of theporous substrate that is opposite the catalytic surface,the second wall and the bottom side forming a secondchannel between the first wall and the bottom side, wherein reactants are enabled to enter the régionvia the second channel and the porous substrate.

50. The apparatus of claim 33, wherein the laserSystem includes: a first laser mirror disposed adjacent to one endof the substrate; a second laser mirror disposed adjacent to anopposite end of the substrate, the first and the secondlaser mirrors forming an optical cavity in the région ofcatalytic surface reaction; and a laser controller surrounding the first lasermirror. 28