CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefit of U.S. Provisional Patent Application No. 61/369,418, filed July 30, 2010 and U.S. Patent Application No. 13/051,051 filed March 18, 2011, which are incorporated by reference in their entirety.

GOVERNMENT INTERESTS

[0002] This invention was made with government support under a grant from the U.S. Army Research Office, contract/grant number W911NF-09-1-0287. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] This invention relates to catalytic compositions, methods for making and using said compositions for the catalytic oxidation of carbon monoxide, and devices derived from said compositions.

BACKGROUND

[0004] Carbon monoxide, a by-product of partial oxidation of carbon containing compounds, is a colorless, odorless and tasteless gas that is highly toxic to humans and animals at sufficient concentrations. Carbon monoxide poisoning resulting in asphyxiation results in more deaths and illnesses than any other chemical in both the military population and the general population at large. Carbon monoxide is known to be difficult to isolate and remove from ambient air at room temperature. For these reasons, greater attention has been focused on removing carbon monoxide from ambient air and converting it to other materials, including carbon dioxide and other oxidized species.

[0005] Catalytic sorbents containing nanoparticles of a catalytic metal dispersed on an active support containing a metal oxide provide a promising option. One catalytic sorbent includes nanoparticles of gold dispersed on an active support of titanium oxide or titania (referred hereinafter as "Au-Ti0 ₂ ")- Au-Ti0 ₂ has been observed to catalytically oxidize carbon monoxide to generate carbon dioxide at relatively low levels of thermal energy input, while effectively sustaining adsorption, reaction and regeneration at normal ambient temperatures. However, Au-Ti0 ₂ exhibits a limited performance profile due to the low surface concentration of hydroxyl ion sites and the relatively low surface area, typically about 50 m ² g ^_1 . In addition, Au- Ti0 ₂ requires precise control of water within a narrow range to optimize reaction conditions. Unfortunately, even mere variability in relative humidity under normal atmospheric conditions can adversely affect the performance of Au-Ti0 ₂ .

[0006] There is a need to provide improved catalysts for relatively low temperature decontamination of carbon monoxide in air streams. There is a further need to provide improved catalysts having elevated levels of porosity and surface area, and ability to form hydroxyl groups from adsorbed water resulting in a greater concentration of active surface functional groups such as hydroxyl groups.

SUMMARY

[0007] Various embodiments of this invention provide compositions comprising nanoparticles of at least one catalytic metal, especially nanoparticles of at least one Group VIII or lib metal, incorporated onto a porous support, said support having a surface comprising at least one hydroxylated metal oxide, wherein the composition is catalytically active for oxidizing carbon monoxide. Additional embodiments include devices comprising these compositions.

[0008] Some additional embodiments include methods of making compositions that are catalytically active for oxidizing carbon monoxide, said methods comprising depositing catalytic metal nanoparticles, especially those of at least one Group VIII or lib metal, onto a porous support having a surface comprising at least one metal oxide or hydroxylated metal oxide.

[0009] Still further embodiments provide methods of removing carbon monoxide from a gas stream or volume comprising contacting said gas stream or volume with a composition comprising catalytic metal nanoparticles, especially nanoparticles of at least one Group VIII or lib metal incorporated onto a porous support having a surface comprising at least one hydroxylated metal oxide, wherein the composition is catalytically active for oxidizing carbon monoxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings are illustrative of embodiments of the invention and are not intended to limit the invention as encompassed by the claims forming part of the invention.

[0011] FIGs 1A-1D show transmission electron microscopy (TEM) images of gold and zirconia samples calcined at about 85°C, respectively, in accordance with one embodiment of the present invention; [0012] FIG. 2A-2D show transmission electron microscopy (TEM) images of gold and zirconia samples calci ned at about 200°C and 500°C, respectively, in accordance with another embodiment of the present invention.

[0013] FIG. 3 is a schematic diagram of a test apparatus implemented for investigating catalytic activity of various zirconia and titania samples in accordance with the present invention.

[0014] FIG. 4 a semi-logarithmic plot of catalytic activity showing a data comparison of carbon dioxide as a percent yield of samples containing gold nanoparticles dispersed on hydroxylated zirconia and titania, respectively, in accordance with the present invention.

[0015] FIG. 5 is a plot of catalytic activity showing data comparison of carbon dioxide as a percent yield of samples containing gold nanoparticles dispersed on hydroxylated zirconia treated at various pH values in accordance with the present invention.

[0016] FIG. 6 is a plot of catalytic activity showing data comparison of carbon dioxide as a percent yield of samples containing gold nanoparticles dispersed on hydroxylated zirconia under different conditions of humidity (dry and 25% RH) in accordance with the present invention.

[0017] FIG. 7 is a plot of catalytic activity showing data comparison of carbon dioxide as a percent yield of samples containing gold nanoparticles dispersed on hydroxylated zirconia at varying temperatures in accordance with the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0018] The present invention relates generally to catalysts useful for low temperature oxidation of carbon monoxide. Broadly, the catalysts of the present invention include a porous support composed of hydroxylated metal oxide loaded with nanoparticles of a catalytic metal. The catalysts of the present invention contain enhanced concentrations of highly dispersed active surface function groups (e.g., hydroxyl groups). The catalysts of the present invention react catalytically upon contact with carbon monoxide to yield carbon dioxide and/or other oxidized species at relatively low, including ambient temperatures. The catalysts of the present invention exhibit enhanced catalytic activity including, high reaction rates and high percent conversion yields of carbon dioxide (CO ₂ ). The catalysts of the present invention can also be readily adapted for various applications requiring decontamination of air streams containing carbon monoxide, and especially for use in portable, semi-portable, or stationary respiratory filtration applications.

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RECTMED SHEET (RULE 91) [0019] The invention involves synthetically-derived nano structures comprising metal oxides which can be modified as a means to influence its properties to provide optimal catalytic performance over a range of operating conditions. The catalysts of the present invention can be designed to operate at normal ambient temperatures and temperatures of less than about 200°C, or even less than about 150°C, and under both dry air conditions and conditions of high relative humidity.

[0020] In order to solve these and other problems in the art, the present invention provides specifically a catalysts or catalytic sorbent having a porous support composed of hydroxylated metal oxide of amorphous composition, and a catalytic metal in the form of nanoparticles loaded on the porous support. The catalysts of the present invention exhibit catalytic reactivity against carbon monoxide, which is effectively neutralized in a rapid and efficient manner. The catalysts of the present invention are physically and chemically stable for use in catalytically reacting and neutralizing carbon monoxide preferably at temperatures between 25 °C to 200 °C, more preferably between 25 °C to 150°C.

[0021] The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying Tables and Figures, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific products, methods, conditions or parameters described and / or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of any claimed invention. Similarly, any description as to a possible mechanism or mode of action or reason for improvement is meant to be illustrative only, and the invention herein is not to be constrained by the correctness or incorrectness of any such suggested mechanism or mode of action or reason for improvement. Throughout this text, it is recognized that the descriptions refer both to the method of preparing articles and to the resulting, corresponding physical articles themselves, as well as the referenced and readily apparent applications for such articles.

[0022] In the present disclosure the singular forms "a," "an," and "the" include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to "a material" is a reference to at least one of such materials and equivalents thereof known to those skilled in the art, and so forth. [0023] When values are expressed as approximations by use of the antecedent "about," it will be understood that the particular value forms another embodiment. In general, use of the term "about" indicates approximations that can vary depending on the desired properties sought to be obtained by the disclosed subject matter and is to be interpreted in the specific context in which it is used, based on its function, and the person skilled in the art will be able to interpret it as such. In some cases, the number of significant figures used for a particular value may be one non- limiting method of determining the extent of the word "about." In other cases, the gradations used in a series of values may be used to determine the intended range available to the term "about" for each value. Where present, all ranges are inclusive and combinable. That is, references to values stated in ranges include each and every value within that range.

[0024] It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Finally, while an embodiment may be described as part of a series of steps or part of a more general composition or structure, each said embodiment may also be considered an independent embodiment in itself.

[0025] Various embodiments of this invention provide catalytic compositions comprising porous supports having a surface comprising at least one hydroxylated metal oxide and having nanoparticles of at least one Group VIII or lib metal thereupon, wherein the composition is catalytically active for oxidizing carbon monoxide.

[0026] Preferably, the hydroxylated metal oxide of the porous support comprises at least one metal or metalloid capable of dissociating adsorbed molecular water and generating hydroxyl groups, which chemically bond to the support surface thereof. As used herein, the term "hydroxylated metal oxide" includes those compositions wherein the corresponding metal or metalloid has at least one nominal hydroxide attached thereto. In the present invention, the hydroxylated metal oxide of the porous support comprises at least one metal element in a hydroxylated state capable of forming and supporting hydroxyl groups dispersed on the surface thereof. In certain cases, these compositions may also be represented or described as hydrated metal oxides; for example, hydroxylated zirconium oxide may be represented as Zr(OH) ₄ or ZrO nH ₂ 0. Illustrative hydroxylated metal oxides which may be used in the porous support include those comprising Al, Ce, Co, Hf, Mg, Ni, Si, Ti, Zr, Zn, and mixtures thereof. [0027] Preferably, the at least one hydroxylated metal oxide comprises a hydroxylated oxide of zirconium or hafnium, and more preferably a hydroxylated oxide of zirconium. Within the group of hydroxylated oxides of zirconium, preferred embodiments include those comprising zirconium (IV) hydroxide or oxyhydroxides of the formula Zr0 ₂ -nH ₂ 0, where 0 < n < 2. Other embodiments include those wherein the hydroxylated zirconia oxides include hydroxylated polymorphic zirconia, zirconium oxyhydroxides, and combinations thereof. These descriptions of zirconia are variations of the same material with slightly different compositions emphasizing adsorbed water or disassociated water as hydroxyls. Hydroxylated zirconia provides enhanced porosity and surface area useful for forming and supporting higher concentration of hydroxyl surface groups.

[0028] In some embodiments, the amount of the hydroxylated metal oxide present in the composition can range from about from about 90% by weight to 99.9% by weight based on the total weight of the composition, and more preferably from about 95% by weight to 98% by weight based on the total weight of the composition.

[0029] The activity of the hydroxylated surfaces is an important feature of the inventive compositions. In certain preferred embodiments, the corresponding anhydrous metal oxide is more basic than Ti0 ₂ . Such is the case, for example, that Zr0 ₂ is more basic than Ti0 ₂ , such that the corresponding hydroxylated zirconia is less Bronsted acidic than the corresponding hydroxylated titania. See F.A. Cotton and G. Wilkinson, Inorganic Chemistry, 4 ^th Ed., 1980, p. 827. In some embodiments, the hydroxylated oxide of zirconium is that composition which is formed by contact anhydrous zirconia with an aqueous solution having a pH in the range of about 3 to about 9. See, for example, FIG. 5. In other more preferred embodiments, the hydroxylated oxide of zirconium is that composition which is formed by contact anhydrous zirconia with an aqueous solution having a pH in the range of about 4 to about 8, and in the range of about 5 to about 7. Independent embodiments include those wherein the hydroxylated oxide of zirconium is formed by contact anhydrous zirconia with an aqueous solution having a pH of about 3, about 4, about 5, about 6, about 7, about 8, and about 9.

[0030] The structure of the porous support may be provided by any material, provide it meets the criteria of porosity and composition and surface coverage of the hydroxylated metal oxides described herein. For example, the support may comprise, for example, carbon beads or activated carbon, e.g., derived from phenolic resin, provided these materials are not deteriorated by the particular conditions to which the composition is exposed during use, and provided the support also contains the hydroxylated metal oxides describe herein. It should be apparent that for applications wherein the catalytic composition is used to process contaminated air for subsequent human consumption that the materials of construction should be non-toxic in such use. Having said this, preferred embodiments are those in which the porous support are aggregates or comprise aggregates of the hydroxylated metal oxides. In these circumstances, the mean particle sizes of the hydroxylated metal oxide particles have a mean particle or crystallite size in the range of about 0.5 nm to about 100 nm, preferably about 0.5 nm to about 50 nm, preferably about 0.5 nm to about 25 nm, preferably about 0.5 nm to about 10 nm, preferable about 0.5 nm to about 5 nm, and preferably about 0.5 nm to about 2 nm. More preferable embodiments are those where the particle or crystallite sizes are less than 2 nm and/or where the hydroxylated metal oxides are microcrystalline (having crystallite sizes of 10 nm or less) or amorphous, most preferably amorphous. Amorphous structures, having crystallite sizes of 10 nm or less provides for formation of elevated concentrations of surface bound hydroxyl groups.

[0031] In other embodiments, the porous support is a xerogel or aerogel, formed for example by sol-gel processing. Hydrogels are gels formed in water, such that the pores are filled with water. In hydrogels, the matrix metal or metal oxide matrices tend to be heavily

hydroxylated making them particularly attractive as porous supports for the present application. An xerogel is a hydrogel with the water removed. An aerogel is a type of xerogel from which the liquid has been removed in such a way as to minimize collapse or change in the pore structure as the water is removed. Alternatively, xerogels or aerogels can be made using sol-gel processing techniques by the addition of water to alcohol based precursor solutions. In preferred embodiments of the present inventive compositions, the liquid is removed from hydrogels or the xerogels / aerogels are processed in such a way as to maintain the high levels of hydroxylated metals or metal oxides as described herein, for example by maintaining processing temperatures to less than about 200°C, less than about 150°C, less than about 100°C, or less than 50°C.

[0032] Depending on the type of process in which the present catalysts or catalytic sorbents is to be used, the porous support can exist in any form including, for example, pellets, monoliths, powders, beds, and the like, which are suitable for promoting maximum contact with an air stream flowing or passing therethrough.

[0033] Preferably, the porous support of the present invention exhibits high micro- and/or meso-pore volume to achieve increased overall surface area. In some embodiments, the porous support has pores having a mean pore size in the range of about 1 nm to about 100 nm. As used herein, the term "pore size" refers to the mean cross-sectional dimension of the pores, as determined by mercury or nitrogen porosimetry. The porous support may be microporous (IUPAC defined as having pore sizes in the range of 0.2 nm to 2 nm) or mesoporous (IUPAC defined as having pore sizes in the range of 2 nm to 50 nm). Independent embodiments provide for the pores of the porous support having a mean pore size range bounded at the lower end of the range as about 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, and 75 nm and at the upper end of the range as about 100 nm, 75 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, and 5 nm; such that exemplary embodiment include those where the mean pore size is in the range of about 1 nm to about 2 nm, about 2 nm to about 10 nm, of about 10 nm to about 50 nm, and about 50 nm to about 100 nm.

[0034] In other embodiments, the porous support has a surface area equivalent to a BET surface area in the range of at least about 50 m ² g ^_1 , more preferably greater than about 100 m ² g ^_1 or greater than about 1000 m ² g ^_1 . In certain more preferred embodiments, the porous support has surface area of about 100 m ² g ^_1 to about 1000 m ² g ^_1 , or in the range of about 1000 m ² g ^_1 to about 1600 m ² g ^_1 , or in the range of about 300 m ² g ^_1 to about 600 m ² g ^_1 .

[0035] The porous support may also be characterized in terms of mean pore volume, in which case certain embodiments provide that the mean pore volume of the porous support in the range of about 0.01 cm ³ g ^_1 to about 0.8 cm ³ g ^_1 , or more preferably in the range of about 0.2 cm ³ g ^{~ 1} to about 0.8 cm ³ g ^_1 .

[0036] The concentration of hydroxyl groups on the surface of the porous support is another important feature of the inventive compositions. Low levels of hydro xylated surfaces provide poor catalytic activity. Accordingly, the present invention provides independent embodiments wherein the hydroxyl groups of the hydroxylated metal oxide cover a portion of the entire surface having a range bounded at the lower limit of about 10%, 20%, 30%, 40%, 50%, or 60% and bounded by an upper limit of about 90%, 80%, 70%, 60%, or about 50%, relative to the entire surface of the porous support. Exemplary ranges include those where the hydroxylated metal oxide covers about 10% to about 90% of the surface (about 0.1 to about 0.9 surface fraction), about 10% to about 60%, about 20% to about 60%, or about 30% to about 50% of the entire surface of the porous support.

[0037] In the inventive compositions, the catalytic metal nanoparticles catalyze the oxidation of the carbon monoxide. The term "catalytic metal" is intended to encompass any metal in a catalytically active state capable of neutralizing, decontaminating or catalytically converting a carbon-containing chemical such as carbon monoxide into one or more oxidized products. Exemplary classes of catalytic metals include transition metals, Group VIII or lib metals, or noble metals.

[0038] In certain embodiments, these metal or metal oxide nanoparticles comprise at least one Group VIII or lib metal. In more preferred embodiments, the metal or metal oxide particle comprises Ru, Rh, Pd, Os, Ir, Pt, Au, or alloys or mixtures thereof. In certain other embodiments, these metal nanoparticles comprise at least one noble metal. In more preferred embodiments, the metal comprises Pt, Pd, Au, or alloys or mixtures thereof. In a more preferred embodiment, the metal comprises Au or alloys thereof. In other embodiments, the

nanop articulate metals or alloys are capable of forming and remaining as metallic clusters or islands when subjected to the catalytic conditions. Compositions characterized as having such clusters or islands are considered separate embodiments.

[0039] As used herein, the term "nanoparticles" refers to a class of materials whose distinguishing feature is that their average diameter, particle or other structural domain size is below about 100 nanometers. The nanoparticles can have an average particle size less than about 100 nm, preferably less than about 50 nm, more preferably less than about 15 nm, and most preferably less than about 10 nm. Independent embodiments include those wherein the mean particle size is about 20 nm, 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1 nm, or 0.5 nm or less. Nanoparticles have very high surface area to volume ratios, which makes them attractive for catalytic applications.

[0040] The catalytic metal is present in a catalytically active amount sufficient to catalytically react with a carbon-containing chemical such as carbon monoxide to yield an oxidized product such as carbon dioxide at relatively low temperatures. In various embodiments, the metal or metal oxide nanoparticles metal constitutes at least about 0.01 wt% relative to the weight of the entire composition. In more preferred embodiments, the metal or metal oxide particles constitutes an amount in the range of about 1 wt% to about 20 wt%, or about 0.1 wt% to about 20 wt%, about 0.1 wt% to about 10 wt%, about 0.1 wt% to about 5 wt%, or about 1 wt% relative to the weight of the entire composition.

[0041] In preferred embodiments, the compositions comprise nanoparticles of gold incorporated into a porous support comprising an amorphous hydroxylated zirconium oxide. In other preferred embodiments, the compositions comprise nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising an amorphous hydroxylated zirconium oxide. In still other preferred embodiments, the compositions comprise nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising amorphous hydroxylated zirconium oxide, wherein the gold nanoparticles are present in an amount in range of about 0.1 wt% to about 20 wt% relative to the weight of the entire composition. In other preferred embodiments, the compositions comprise nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising amorphous hydroxylated zirconium oxide, wherein the porous support has surface area in the range of about 100 m ² g ^_1 to about 1000 m ² g ^_1 and wherein the gold nanoparticles are present in an amount in range of about 0.1 wt% to about 20 wt% relative to the weight of the entire composition. In each of these embodiments, the composition is capable of oxidizing carbon monoxide at relatively low temperatures (e.g., less than about 150°C).

[0042] To this point, the various described embodiments have described compositions, but the invention presented here is not limited to compositions. Additional embodiments include devices, including gas purification devices, which contain or include the compositions described above. Further embodiments also provide for devices comprising at least one heating element, configured so as to provide heating of the composition while allowing a source of gas to contact the surface and/or penetrate the porosity of the compositions described above. Various of these devices can be used to reduce the concentration of carbon monoxide from a vehicle exhaust emission, a gas used in a C0 ₂ laser, a gas used in a fuel cell and/or ambient air undergoing air filtration. The catalyst may be incorporated into a in an amount effective to oxidize carbon monoxide to carbon dioxide. The catalyst can be used in an air filter for the conversion of carbon monoxide and/or indoor volatile organic compounds.

[0043] The present invention also provides methods for making the compositions described above. Certain embodiments include methods of making compositions that are catalytically active for oxidizing carbon monoxide, said methods comprising depositing catalytic metal nanoparticles, especially those of at least one Group VIII or lib metal, onto porous supports having a surface comprising at least one hydroxylated metal oxide or hydroxylated metal oxide. Included in this class of embodiments are those wherein the methods result in compositions described above and having the characteristics thereof.

[0044] Some of these embodiments include those methods wherein the metal is deposited by co-precipitation, deposition, impregnation, or a combination thereof. The catalytic metals or metal oxides can be formed by such methods as, for example, deposition-precipitation or co-precipitation or in situ upon heating a mixture of suitable metal precursor compounds. Metal nanoparticles may also be incorporated into the support by various methods, such as, for example, ion exchange, impregnation, physical admixture, deposition-precipitation, co- precipitation, in situ precipitation by urea hydrolysis, and/or hydrothermal methods. For example, the metal precursor may be dissolved or suspended in a liquid, and the support may be mixed with the liquid having the dispersed or suspended metal precursor. The dissolved or suspended metal precursor can be adsorbed onto a surface of the support or absorbed into the support. The metal precursor may also be deposited onto a surface of the support by removing the liquid, such as by evaporation so that the metal precursor remains on the support. The liquid may be substantially removed from the support during or prior to thermally treating the metal precursor, such as by heating the support at a temperature higher than the decomposition temperature of the precursor or by reducing the pressure of the atmosphere surrounding the support. Further embodiments provide methods comprising infiltrating the porous support with a salt of the metal and subsequently reducing the metal salt, either chemically (for examples, using hydrogen gas, borohydride, or other chemical reducing agent) or electrolytically.

[0045] Additional embodiments include methods of making a composition that is catalytically active for oxidizing carbon monoxide, said methods comprising organizing a porous support having a surface comprising at least one metal oxide or hydroxylated metal oxide around nanoparticles of at least one Group VIII or lib metal. Included in this class of embodiments are those wherein the methods result in compositions described above and having the characteristics thereof.

[0046] For example, nanoparticles can be formed in situ upon heating a mixture of a suitable metal precursor compound and support. By way of a non- limiting example, a metal precursor compound, such as gold hydroxide, can be dissolved in a suitable solvent, such as alcohol, and mixed with a dispersion of a support material, such as colloidal silica, or a support material precursor, such as a zirconate gel precursor, which can be gelled in the presence of an acid or base and allowed to dry such as by drying in air. Acids and bases that can be used to gel the colloidal or precursor mixture include hydrochloric acid, acetic acid, formic acid, ammonium hydroxide and the like. When an acid containing chlorine is used to gel the colloidal mixture, preferably the gel is washed in de-ionized water in order to reduce the concentration of chloride ions in the gel. During or after gelation, the metal precursor-colloidal metal or metalloid precursor mixture can be heated to a relatively low temperature, for example 200-400°C. , wherein thermal decomposition of the metal precursor results in the formation of metal nanoparticles or metal oxides on silica support particles. [0047] Additional embodiments include those methods wherein the at least one metal oxide is further subjected to conditions sufficient to hydroxylate the at least one metal oxide. These conditions may include subjecting an anhydrous metal oxide or partially hydroxylated metal oxide, to an aqueous medium having a pH in the range of about 3 to about 9, preferably having a pH in the range of about 4 to about 8, preferably in the range of about 5 to about 7, and more preferably in the range of about 6 to about 7.

[0048] In one exemplary series, the present composition is prepared by obtaining a hydroxylated form of a metal oxide such as hydroxylated zirconia, which is commercially prepared and available from various chemical supply vendors. The hydrous form of the metal oxide is calcined at an elevated temperature for a period of time. The calcined hydrous form of the metal oxide is then loaded with nanoparticles of a corresponding catalytic metal such as gold through any suitable means including, but not limited to, colloidal deposition, to yield the present catalyst sorbent. During the loading process, the resulting catalyst sorbent can be treated to adjust the pH between 3 and 9 using solutions of sodium hydroxide (NaOH) and hydrochloric acid (HC1).

[0049] In a particular example, a hydroxylated form of zirconia (designated herein as Zr0 ₂ ) was commercially prepared by Magnesium Elektron Inc. of Flemington, New Jersey. The hydroxylated form of zirconia was calcined at an elevated temperature in the range of from about 85°C to 500°C, preferably from about 85°C to 200°C, for about six hours, and then loaded with gold nanoparticles via the process of colloidal deposition. This involved the preparation of reduced gold nanoparticles from a solution of AuCb-HCl (7.5 ml, 0.008 M). The solution was diluted to 150 mL with 18 Mohm deionized water. To produce a sample with a particular pH between 3 and 9, the pH of the resulting solution was adjusted using 0.1 M NaOH and HC1. 1 mL of PVA (1 wt% in water) was added to the solution. The resulting solution was stirred at room temperature for about 2 hours. 120 μΐ NaBH ₄ (0.5 M in 2-methoxyethyl ether) were added drop-wise resulting in a clear red solution.

[0050] The clear red solution containing reduced gold nanoparticles was added drop- wise to 100 ml deionized water containing 0.5 g Zr0 ₂ -85 and followed by rapid stirring for about 12 hours at room temperature. The resulting sample solution was filtered, washed with distilled deionized water and dried at 85°C. The resulting catalytic sorbent sample contained about 2.0 wt% Au. [0051] With reference to FIGs. 1A, IB, 1C, and ID, samples of zirconia were calcined at about 85°C (Zr0 ₂ -85) with some loaded with gold nanoparticles utilizing the method described above. The samples exhibited an aggregate particle size in the range of from about 10 to 100 microns. The samples were sonicated in 1 mL of methanol for about 10 minutes and transferred to carbon grids via a micro-liter pipette. A high resolution transmission electron microscopy (JEOL2100 operated at 200 KV) was used to observe the morphology of the samples.

[0052] Micrographs of FIGs. 1A and IB show Zr0 ₂ -85 absent gold nanoparticles at low and high magnifications, respectively, and the micrographs of FIGs. 1C and ID show gold nanoparticle-dispersed Zr0 ₂ -85 at low and high magnifications, respectively. The zirconia support of the micrographs of FIGs. 1A and IB, respectively, clearly indicates a distribution of irregular shaped crystalline particles containing primarily monoclinic-Zr0 ₂ surfaces with a mean particle size of 7.0 nm +/- 3 nm (1σ). In contrast, the morphology of the gold nanoparticles shows discreet particles with a mean particle size of 4.0 nm +/- 1 nm (1σ) that are highly dispersed and intercalated between Zr0 ₂ clusters.

[0053] Referring to FIGs 2A, 2B, 2C and 2D, respectively, samples of zirconia were calcined at either 200°C (ZrO ₂ -200) or 500°C (ZrO ₂ -500) with select samples loaded with gold nanoparticles utilizing the method described above. The micrographs of FIGs 2A and 2B show ZrO ₂ -200 absent gold nanoparticles and ZrO ₂ -200 loaded with gold nanoparticles, respectively. The sample of ZrO ₂ -200 shown in the micrographs of FIG 2A exhibited clusters of Zr0 ₂ ranging in size of from about 5 nm to 10 nm and composing amorphous-like particles of short range order. The sample of ZrO ₂ -200 shown in the micrograph of FIG 2B contained about 2 wt% of gold nanoparticles ranging in size of from about 1 nm to 5 nm, and highly dispersed on the Zr0 ₂ - 200 support. As shown in the micrograph of FIG 2B, the structural characteristics of the Zr0 ₂ - 200 support remain unchanged with the addition of the gold nanoparticles.

[0054] The sample of ZrO ₂ -500 as shown in the micrograph of FIG 2C exhibits a dramatic change in crystal growth with particles ranging in size of from about 15 nm to 30 nm. The sample of ZrO ₂ -500 shown in the micrograph of FIG 2D contained about 2 wt% of gold nanoparticles ranging in size of from about 1 nm to 5 nm, and highly dispersed on the ZrO ₂ -200 support. As further shown in the micrograph of FIG 2D, the structural characteristics of the ZrO ₂ -500 support remain unchanged with the addition of the gold nanoparticles.

[0055] These compositions, and the devices incorporating these compositions, can be used to catalyze the oxidation of carbon-containing compounds including carbon monoxide. Certain embodiments provide methods of removing carbon monoxide from a gas stream or volume comprising contacting said gas stream or volume with a composition comprising catalytic metal nanoparticles, especially nanoparticles of at least one Group VIII or lib metal incorporated onto a porous support having a surface comprising at least one hydroxylated metal oxide, wherein the composition is catalytically active for oxidizing carbon monoxide. Included in this set of embodiments are those wherein the methods derived from the embodied compositions described above and having the characteristics thereof.

[0056] The catalytic compositions of the present invention can be implemented or employed in various suitable arrangements of process conditions, depending upon the nature of the air streams to be purified. It will be understood that the present invention is not limited to the detoxification, neutralization or decontamination of carbon monoxide, and may encompass the detoxification, neutralization or decontamination of any toxic chemicals in the air streams through contact with the catalytic metal and hydroxylated metal oxide combination to produce a reaction product that is less toxic and safer than the initial toxic industrial chemical. Mere physical contact of the toxic chemical with the present catalytic sorbent is sufficient to initiate the decontamination process.

[0057] The catalytic compositions of the present invention is useful in greatly reducing or eliminating carbon-containing chemicals from an air stream passing therethrough and releasing oxidized products back into the passing air stream. In a preferred embodiment of the present invention, the catalytic compositions are used to catalytically convert carbon monoxide into carbon dioxide for release back into the air stream. The conditions required for carrying out the claimed methods can generally be described as ambient environmental conditions.

[0058] In various of these methods, the composition is at a temperature in the range of about 25°C to about 200°C, more preferably in the range of about 25°C to about 150°C, and more preferably in the range of about 25°C to about 100°C.

[0059] In some embodiments, the methods catalyze the oxidation of carbon monoxide. In other embodiments, methods catalyze the oxidation of carbon monoxide to carbon dioxide or a carbonate derivative thereof.

[0060] In preferred embodiments, the methods comprise oxidizing carbon dioxide at temperatures of about 200°C or less by contacting a composition containing carbon monoxide with a composition comprising nanoparticles of gold incorporated into a porous support comprising an amorphous hydroxylated zirconium oxide. In other preferred embodiments, the methods comprise oxidizing carbon dioxide at temperatures of about 150°C or less by contacting a composition containing carbon monoxide with a composition comprising nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising an amorphous hydroxylated zirconium oxide. In still other preferred embodiments, the methods comprise oxidizing carbon dioxide at temperatures of about 150°C or less by contacting a composition containing carbon monoxide with a the compositions comprising nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising amorphous hydroxylated zirconium oxide, wherein the gold nanoparticles are present in an amount in range of about 0.1 wt% to about 20 wt% relative to the weight of the entire composition. In other preferred embodiments, the methods comprise oxidizing carbon dioxide at temperatures of about 150°C or less by contacting a composition containing carbon monoxide with a compositions comprise nanoparticles of gold, having a mean particle size of less than 10 nm, incorporated into a porous support comprising amorphous hydroxylated zirconium oxide, wherein the porous support has surface area in the range of about 100 m ² g ^_1 to about 1000 m ² g ^_1 and wherein the gold nanoparticles are present in an amount in range of about 0.1 wt% to about 20 wt% relative to the weight of the entire composition. In each case, the composition containing carbon monoxide may be a static or streaming mixture.

[0061] It is noted that while these compositions and methods are described in terms of the ability to oxidize carbon monoxide, they may also be used to oxidize other volatile organic materials toward which they show activity. Similarly, given the pore sizes described herein, they may also be useful to the removal of particulate matter contained within the gas to be treated.

[0062] When the catalyst promotes oxidation of carbon monoxide, a significant reduction in the amount of carbon monoxide can be achieved under certain test conditions.

Preferably, at temperatures in the range of about 25° to about 150°C, greater than 25 weight % or greater than 50 weight % of carbon monoxide is oxidized, more preferably greater than 80 weight % of carbon monoxide is oxidized, even more preferably greater than 90 weight % of carbon monoxide is oxidized, and most preferably 100 weight % of carbon monoxide is oxidized within 60 minutes, within 10 minutes, within 5 minutes, or within 2 minutes using a gas stream or static volume comprising carbon monoxide in helium or argon, air, and oxygen.

[0063] While not intending to be bound by theory, it is believed that the highly dispersed hydroxyl (OH) groups contained on the porous support of the present invention, function in place of water molecules to decompose any carbonate formed from the intermediate reaction of carbon monoxide, which stabilizes the catalytic activity of the gold nanoparticles. The increased surface area in the porous support facilitates the accommodation of larger concentrations of the active surface functional groups such as hydroxyls in combination with the dispersed gold nanoparticles. It is further believed that the surface hydroxyl groups participate in a complex series of reactions involving molecular oxygen and water. The hydroxyl groups in combination with the gold nanoparticles promote the initial reaction of carbon monoxide to yield a carbonate compound. The hydroxyl groups facilitate the formation of superoxide (0 ₂ ^~ ), which reacts and oxidizes the carbonate compound to yield carbon dioxide.

[0064] The present subject matter is further defined in the following Examples. It should be understood that these examples, while indicating preferred embodiments of the subject matter, are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this subject matter, and without departing from the spirit and scope thereof, can make various changes and modifications of the subject matter to adapt it to various usages and conditions. Such modifications are considered to be within the scope of the present invention.

EXAMPLES

[0065] The following examples serve to provide further appreciation of the invention but are not meant in any way to restrict the effective scope of the invention.

Example 1: Preparation of a Catalytic Sorbent of the Present Invention

[0066] A hydroxylated form of zirconia (designated herein as Zr0 ₂ ) commercially prepared and available from Magnesium Elektron Inc. of Flemington, New Jersey was obtained. The as-received Zr0 ₂ samples contained water in amounts of from about 0.24 to 0.28 gram per gram Zr0 ₂ . The Zr0 ₂ sample (designated herein as Zr0 ₂ -85) was calcined at a temperature of about 85°C for about six hours. The Zr0 ₂ -85 sample was then loaded with gold nanoparticles via colloidal deposition. The deposition technique used is similar to methods disclosed in Prati et al, Topics in Catalysis, 2009, 52, 288-296, and Comotti et al, Topics in Catalysis, 2007, 44, 275-284, each of which is hereby incorporated by reference.

[0067] The deposition involved the preparation of reduced gold nanoparticles from a solution of AuCl ₃ -HCl (7.5 ml, 0.008 M). The solution was diluted to 150 mL with 18 Mohm deionized water. To produce a sample with a particular pH between 3 and 9, the pH of the resulting solution was adjusted using 0.1 M NaOH and HCl. PVA (1 mL of 1 wt% in water) was added to the solution. The resulting solution was stirred at room temperature for about 2 hours. NaB]¾ (120 μΐ 0.5 M) in 2-methoxyethyl ether were added drop-wise resulting in a clear reddish orange solution.

[0068] The clear reddish-orange solution containing reduced gold nanoparticles was added drop-wise to 100 ml de-ionized water containing 0.5 g Zr0 ₂ -85 followed by rapid stirring for about 12 hours at room temperature. The resulting sample solution was filtered, and washed with distilled de-ionized water. It is noted that for mid- and high-range pH preparations, the filtrate solution was clear and colorless indicating that nearly all of the gold was deposited on the metal oxide. At low pH, the filtrate solution contained a significant amount of gold based on the appearance of the reddish clear solution. The filtrate solution was dried at 85°C to yield a sample of Au/Zr0 ₂ -85. The resulting Au/Zr0 ₂ -85 sample contained about 2.0 wt% Au.

Example 2: Comparative Samples of Catalysts of the Present Invention and Titania-based Catalysts and their Textural Properties

[0069] Samples of catalytic sorbents of the present invention were prepared from a hydroxylated form of zirconia (designated herein as Zr0 ₂ ). The hydroxylated form of zirconia was obtained commercially prepared and available from Magnesium Elektron Inc. of

Flemington, New Jersey. The as-received Zr0 ₂ contained water in amounts of from about 0.24 to 0.28 gram per gram Zr0 ₂ . The samples of Zr0 ₂ were divided into different groups. One group (designated herein as Zr0 ₂ -85) was calcined in a static oven at a temperature of about 85°C for about six hours. A second group (designated herein as ZrO ₂ -200) was calcined in a static oven at a temperature of about 200°C for about 6 hours. A third group (designated herein as ZrO ₂ -500) was calcined in a static oven at a temperature of about 500°C for about six hours.

[0070] Three titania substrates or supports, Ti-ana (101), Ti-iso (101) and Ti-nt (001), were selected and prepared for comparison with the zirconia supports. The titania supports were selected based on higher performance results, and representation of various structures and morphologies. Ti-ana, a low porosity anatase, was obtained in the form of a nanopowder (-25 nm) from Sigma- Aldrich of St. Louis, Missouri. Ti-iso was prepared by hydrolysis of titania isopropoxide in a water-alcohol solution at room temperature, filtered, washed and dried at 85°C. Titania isopropoxide was obtained from Sigma- Aldrich. Ti-nt, a hydroxylated titania nanotube powder with aggregates ranging in size of from about 5 μιη to 10 μιη, was synthesized using the method disclosed in Mogilevsky et al., Chemical Physics Letters, 2008, 460, 517-520, the content of which is hereby incorporated by reference. The titania supports were calcined in a static oven at a temperature of about 85°C for about six hours. [0071] The Zr0 ₂ and titania supports were loaded with gold nanoparticles using the method described in Example 2. The clear reddish-orange solutions containing reduced gold nanoparticles were added drop-wise to 100 ml deionized water containing 0.5 g Zr0 ₂ -85, Zr0 ₂ - 200, ZrO ₂ -500, Ti-ana, Ti-iso and Ti-nt, respectively, each followed by rapid stirring for about 12 hours at room temperature. The resulting sample solutions were filtered, washed with distilled deionized water and dried at 85°C to yield the gold nanoparticle loaded samples. Each sample contained about 2.0 wt% Au.

[0072] The textural properties derived from nitrogen isotherms measured for several zirconia and titania samples are listed in Table 1 below.

[0073] The data indicates a dramatic loss in porosity for the Zr0 ₂ samples with increasing calcination temperature, with BET surface areas decreasing from 532 m ² /g to 108 m ² /g over a temperature range of 85°C to 500°C. Similarly, the micropore volume (Vmicro) decreased from 0.18 ml/g to 0.054 ml/g over the same temperature range. Although not reported, the addition of gold nanoparticles to zirconia and titania resulted in a negligible change in BET surface areas and micropore volumes.

Example 3: Catalytic Carbon Monoxide Oxidation Test Apparatus [0074] A study was initiated to report the properties and catalytic activities of a hydroxylated polymorphic zirconia comprising a mixture of Zr(OH)4-nH ₂ 0 and crystalline Zr0 ₂ -nH ₂ 0, supporting gold nanoparticles, and various titania supports, using a test apparatus 30 shown in FIG. 3.

[0075] As shown in FIG. 3, the test apparatus 30 was used for measuring the activity of catalyst materials by means of exposing a sample catalyst to a known concentration of chemical adsorbate. The test apparatus 30 consists of a closed-circuit construction through which a gas mixture is circulated through a bed of sample catalyst at fixed airflow velocities. The test apparatus includes a syringe 32 containing a chemical adsorbate (i.e., carbon monoxide), a chemical injection port 34 for receiving the chemical adsorbate from the syringe 32, and a stream selection valve 36 for directing the gas mixture through either a sample bypass loop 38 or a sample testing loop 40. The sample testing loop 40 includes a temperature controlled sample cell 42 with a quartz frit sample support 44. The sample bypass loop 38 and the sample testing loop 40 are each connected to a roto meter 46 for controlling flow rate, a pump 48, a Fourier transform infrared (FTIR) detector 50, and a mixing ballast 52.

[0076] The gas phase concentration of primary adsorbate and reaction product(s) are measured downstream from the sample cell 42 by the FTIR detector 50. The gas mixture is returned to the sample cell repeatedly by the pump 48. During testing, the FTIR detector 50 monitors the concentration of the adsorbate and the reaction products. In the case of carbon monoxide oxidation with catalyst, carbon dioxide is formed and released into the gas phase. The depletion of carbon monoxide and the increase in carbon dioxide formation is monitored concurrently with the FTIR detector 50.

[0077] The sample cell 42 comprises a 15 cm long glass tube 54 with a 10 mm inside diameter and 15 mm outside diameter. The sample cell 42 includes a 3/8-inch metal coupling fused to each end of the glass tube 54. The metal couplings are fitted with a Swagelok 3/8 inch nut and ferrule for connection to sample lines. A resistive heating wrap (not shown) enveloping the glass sample tube 54 is used to regulate the temperature of the sample cell 42. A

thermocouple (not shown) is placed between the heat wrap and the glass tube 54 to monitor the temperature.

[0078] The quartz frit sample support 44 is disposed within the glass sample tube 54 for retaining the catalyst sample. The frit sample support 44 is porous to allow the gas mixture to pass through the catalyst sample. The flow is maintained in the downwardly direction to prevent fluidizing of the catalyst sample. The rotometer 46 regulates the gas flow rate through the tube 54. The pump 48 is a bellows pump containing stainless-steel reed valves. The flow rate is typically 250 ml/min during activity measurements, but can be adjusted from zero to about 3000 ml/min.

[0079] A stream selection valve 36 is disposed upstream from the sample cell 42 to direct the flow of the gas mixture into the sample cell 42 or to bypass the sample cell 42. The bypass loop 38 allows the gas mixture concentration to be established before exposure to the sample catalyst retained within the sample cell 42.

[0080] The gas mixture concentration is based on the mass of chemical injected into the test apparatus 30 and the total volume of the test apparatus 30. The volume of the test apparatus 30 comprises the mixing ballast 52 at 6.0 L and the cell of the FTIR detector 50 at about 2.0 L. The total system volume including tubing, valves and connecting fittings is 8.77 L.

Example 4: Catalytic Carbon Monoxide Oxidation Testing and Comparison

[0081] The activities of zirconia- and titania-based catalysts of Example 2 were investigated based on the oxidation of carbon monoxide (CO) to carbon dioxide (C0 ₂ ) in air under humid and dry conditions, respectively. The activities were ranked based on the calculated %C0 ₂ yield and rate of CO reaction (or C0 ₂ formation) expressed as mol-CO/mol-Au-s.

[0082] The following test conditions were used for all catalyst samples in the test apparatus 30: sample cell temperature was in the range of from about 25°C to 125°C, initial carbon monoxide concentration was about 1200 ppm in purified air, sample weight was about 100 mg, CO feed rate initial was about 0.2 μιηοΐ/s, flow rate through catalyst bed was about 250 ml/min, relative humidity was about 25% (at 25 °C) or dry air, and space velocity was about 75,000 h ^"1 .

[0083] A comparison was made for various Au/Zr0 ₂ and Au/Ti0 ₂ catalyst samples, each prepared at pH 6.4 and calcined at 85°C. FIG. 4 shows a semi- logarithmic plot illustrating low and high concentrations of catalytic activity for carbon monoxide conversion in samples containing Zr0 ₂ -85, Au/Zr0 ₂ -85, Au/Ti-ana-85 , Au/Ti-/so-85 and Au/Ti-ni-85. Clearly, the performance for each of the Au/Zr0 ₂ -85 materials exceeds that of the titania supported catalysts (the same size and concentration of gold nanoparticles) by a factor of four or more. Pure zirconia, with no gold nanoparticles attached, shows very weak activity (2% or less conversion), supporting that gold is acting as the catalyst. [0084] A determination of the catalytic activity of Au/Zr0 ₂ calcined at 85 °C was made based on various acid-base treatments in the range of from about pH 3 to 9. The feed stream of the testing apparatus 30 was set at 1200 ppm CO, 21 vol% 0 ₂ , 79 vol% N ₂ , and 25% relative humidity. FIG. 5 shows the measured catalytic activity in terms of percent C0 ₂ yield after 500 seconds of exposure to the CO/water mixture. The results of the pH evaluation, clearly indicate that maximum conversion (reported as %C0 ₂ yield) occurred at a pH of about 6.4 (66.1% carbon dioxide yield) followed by 33% and 16% carbon dioxide yield at pH 9 and 3, respectively. The effect of pH treatment and catalyst activity is likely related to the ratio of cations and anions in solution containing gold nanoparticles and the surface of the metal oxide. Under neutral conditions (point of zero charge, "pzc") the surface environment is ionic neutral. The pzc for the zirconia and titania supports occur near pH 6.4.

[0085] To understand the effect of calcination temperature on carbon monoxide oxidation activity, Au/Zr0 ₂ catalysts were evaluated over a temperature range of 85 °C to 500°C. Each of the samples was prepared at pH 6.4. As shown in Table 2, calcination temperature dramatically changes catalyst activity with the highest performance occurring in the range of 85°C (66.1% carbon dioxide yield) to 200°C (14.8% carbon dioxide yield). At the highest temperature, 500°C, catalyst activity decreased markedly to less than 5.4% carbon dioxide yield. The observed trend in catalyst activity was anticipated due to a similar decrease in porosity with increasing calcination temperature. In fact, the change in activity with calcination temperature is roughly proportional to the change in BET surface area. In addition, it has been reported that significant loss of surface hydroxyl groups occurs above 200°C, thus further reducing the number of active sites available for reaction.

[0086] Considering the trends discussed above, a comparison was made for various Au/Zr0 ₂ catalyst samples prepared at pH 6.4 and calcined at 85°C and 200°C, respectively. The feed stream of the testing apparatus 30 was set at 1200 ppm CO, 21 vol% 0 ₂ , 79 vol% N ₂ , and 25% RH or dry. FIG 6 shows plotted data illustrating low and high concentrations of catalytic activity for carbon monoxide conversion in samples containing Au/Zr0 ₂ -85, and Au/ZrO ₂ -200 tested at 25% RH (relative humidity) and dry conditions. When tested at 25% RH conditions the performance of the Au/Zr0 ₂ -85 material exceeds that of the Au/ZrO ₂ -200 catalyst samples (the same size and concentration of gold nanoparticles) by a factor of four or more. When tested under dry conditions the overall performance is approximately 50% lower than at 25% RH conditions. Similarly the Au/Zr0 ₂ -85 catalyst performed better than the Au/ZrO ₂ -200 catalyst under dry conditions. [0087] A summary of carbon monoxide conversion rates and percent carbon dioxide yield referenced at 500 seconds (time of exposure to CO) is provided in Table 2 below.

[0088] For the Au/Zr0 ₂ samples calcined at 85°C, 200°C and 500°C (pH 6.4), a significant increase in carbon monoxide conversion rate is observed from 0.0038 to 0.0454 mol- CO/mol-Au-s, respectively, while the percent carbon dioxide yield decreased from a maximum of 66.1 % and 14.8% (for the 85°C and 200°C samples) to 5.4 % for the Au/ZrO ₂ -500 sample.

[0089] FIG. 7 provides plotted data of catalytic activities showing a data comparison of carbon dioxide as a percent yield of samples containing gold nanoparticles dispersed on hydroxylated zirconia at various temperatures. The feed stream of the testing apparatus 30 was set at 1200 ppm CO, 21 vol% 0 ₂ , 79 vol% N ₂ , and 25% relative humidity. The temperature trend shows that the catalyst activity increases with increasing temperature of the feed stream over a range of from 25°C to 125°C. At 1000 seconds (time of exposure to CO), the percent C0 ₂ yield is about 15% and increases to about 35% when the temperature is increased to 50°C. At 75°C, the percent C0 ₂ conversion yield is about 42%, and with further increase in temperature to 100°C and 125°C, the C0 ₂ yield increases to about 75 and 90%, respectively.

[0090] Unlike previously reported zirconia materials, where loss of surface hydroxyl groups and reduced porosity resulted from high temperature calcinations, the present hydroxylated form of zirconia shows significant improvement in carbon monoxide oxidation activity. A key factor for this form of zirconia is the ability to adsorb and dissociate water rapidly, thus sustaining the oxidation process. The interaction of water with metal oxide surfaces characterized by hydrogen and oxygen exchange is a critical factor in applications requiring highly efficient catalytic materials. Furthermore, the porosity of the catalyst support plays an important role by providing a high concentration of active sites while enabling higher turnover rates and conversions.

[0091] For the most stable forms of zirconia, water is entirely dissociated, which is likely influenced by interaction through hydrogen bonding between hydroxyl groups adsorbed on neighboring cationic sites. In contrast, titania' s interaction with water involves whole molecules participating in adsorption and dissociation which is surface coverage dependent. The specific interactions involving water with polymorphic structures is likely responsible for the differences in catalytic performance that we observed in this evaluation.

[0092] In summary, this study reports the exceptional carbon monoxide oxidation activity of a novel catalyst: micro/meso-porous hydroxylated zirconia of polymorphic composition supporting gold nanoparticles. Hydroxylated zirconia provides a better support for gold catalyst than titania, which was considered to be the most efficient catalytic support until now. This study also demonstrated the effect of calcination temperature on structural transformation of amorphous zirconia to the polymorphic crystalline forms with reduction in porosity, as well as the reduction in carbon monoxide activity with loss of surface hydroxyl groups. With further work in elucidating the relationship of surface hydroxyl groups and microporosity of metal oxides, improved strategies for tailoring properties of functional catalysts can be developed.

[0093] As those skilled in the art will appreciate, numerous modifications and variations of the present invention are possible in light of these teachings, and all such are contemplated hereby. For example, in addition to the embodiments described herein, the present invention contemplates and claims those inventions resulting from the combination of features of the invention cited herein and those of the cited prior art references which complement the features of the present invention. Similarly, it will be appreciated that any described material, feature, or article may be used in combination with any other material, feature, or article.

[0094] The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.