HETEROGENEOUS CATALYSTS/PROCESS BASED ON SUPPORTED/GRAFTED TRANSITION METAL HYDRIDES FOR AMMONIA FORMATION FROM NITROGEN AND HYDROGEN

Abstract

Disclosed is a catalyst and process for producing ammonia (NH.sub.3). The process includes contacting a gaseous feed mixture comprising nitrogen (N.sub.2) and hydrogen (H.sub.2) with a metal hydride material under reaction conditions sufficient to produce a product stream comprising NH.sub.3.

Claims

1. A process for producing ammonia (NH.sub.3) comprising contacting a gaseous feed mixture comprising nitrogen (N.sub.2) and hydrogen (H.sub.2) with a supported metal hydride material under reaction conditions sufficient to produce a product stream comprising NH.sub.3, the metal hydride material has the formula:
[(R).sub.xMH.sub.y] where: M is a transition metal; R is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0x; 1y; and x+y is equal to the valence of M, and the support is dehydroxylated silica (SiO.sub.2).

2. The process of claim 1, wherein the reaction conditions comprise a temperature from 15 C. to 260 C., 100 C. to 200 C., preferably 150 C., a pressure of atmospheric pressure or 0.1 MPa to 2 MPa, 1 MPa to 2 MPa, preferably 1.5 MPa or both.

3. The process of claim 1, wherein a volume ratio of N.sub.2 to H.sub.2 (N.sub.2:H.sub.2) is 1:1 to 1:4, preferably 1:3.

4-5. (canceled)

6. The process of claim 1, wherein R comprises 1 to 7 carbon atoms, preferably 1 to 5.

7. The process of claim 6, wherein R is a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, neopentyl, hexyl group, or combinations thereof.

8. The process of claim 1, wherein the transition metal is scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), Lanthanide series, lanthanum (La), cerium (Ce), Actinide series, rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt), darmstadtium (Ds), roentgenium (Rg), or copernicum (Cn) or any alloy thereof.

9. The process of claim 1, wherein the transition metal is Ta, Ti, Zr, Hf, Mo, or W, preferably Ta or Ti.

10. The process of claim 9, wherein the transition metal is Ta, and metal hydride material has a general structure of: ##STR00008## where R.sub.1 and R.sub.2 are each individually a hydrogen, a hydrocarbon, a substituted hydrocarbon group, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof.

11. The process of claim 10, wherein R.sub.1 and R.sub.2 are each hydrogen.

12. The process of claim 1, where the transition metal is Ti, and the metal hydride material has the general structure: ##STR00009##

13. The process of claim 1, wherein the metal hydride material further comprises a second metal hydride material having the general formula:
[(R.sub.2).sub.tM.sup.2H.sub.u] where: M.sup.2 is a transition metal with the proviso that M and M.sup.2 are different; R.sub.2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0t; 1u; and t+u is equal to the valence of M.sup.2.

14. The process of claim 1, wherein the metal hydride material is in the form of a molecular complex, a molecular cluster, or a nanoparticle.

15. The process of claim 1, wherein a portion of the ammonia is adsorbed on the metal hydride material.

16. A supported metal hydride material capable of catalyzing the production of ammonia from nitrogen (N.sub.2) and hydrogen (H.sub.2), the metal hydride material having the formula of:
[(R).sub.xMH.sub.y] where: M is a transition metal; R is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0x, 1y, and x+y is equal to the valence of M, and the support is double dehydroxylated SiO.sub.2 wherein the metal hydride material is capable of catalyzing the production of ammonia from a mixture of nitrogen and hydrogen.

17. (canceled)

18. A method for preparing any one of the metal hydride materials of claim 16, the method comprising: (a) obtaining a solution comprising an hydrocarbon anion (R.sup.); (b) reacting R.sup. with a transition metal (M) precursor to form a hydrocarbon metal (R.sub.xM) material, where x is equal to the valence of M (c) contacting the RAM with a double dehydroxylated silica support material to form a supported R.sub.xM material; and (d) treating the R.sub.xM material with hydrogen (H.sub.2) under conditions sufficient to form the catalyst having the general formula of:
[(R).sub.xMH.sub.y] where: M is a transition metal; R is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0x, 1y, and x+y is equal to the valence of M; and (e) drying the material of step (d).

19. (canceled)

20. The method of claim 18, further comprising: (i) obtaining a [(R.sub.2).sub.tM.sup.2H.sub.u] material, where: M.sup.2 is a transition metal R.sub.2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0t, 1u, and t+u is equal to the valence of M.sup.2; and (ii) adding the material of step (i) to the compound of step (e).

21. The process of claim 1, wherein the catalyst is ##STR00010##

22. The process of claim 1, wherein the metal is Ta and the support is binuclear dehydroxylated SiO.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0031] FIG. 1 shows a schematic of a one reactor system to produce ammonia of the present invention.

[0032] FIG. 2 shows a reaction schematic for the formation of a supported metal hydride of the present invention ((SiO)TiH.sub.y) and its use to catalyze the formation of NH.sub.3 from N.sub.2 and H.sub.2.

[0033] FIG. 3 shows the NMR spectrum of the [(SiO)TiH.sub.y] of the present invention.

[0034] FIG. 4 shows stepwise in-situ IR spectrums of [(SiO)TiH.sub.y] of the present invention during reaction with N.sub.2 and H.sub.2 under various heat treatment temperatures.

[0035] FIG. 5 shows the reaction schematic for the formation of [(SiO).sub.xTaH.sub.y] of the present invention.

[0036] FIG. 6 shows the .sup.1H NMR spectrum of [(SiO).sub.xTaH.sub.y] of the present invention.

[0037] FIG. 7 shows the .sup.15N-MAS NMR spectrum of [(SiO).sub.xTaH.sub.y] of the present invention after treatment with .sup.15N.sub.2 and H.sub.2 at room temperature.

[0038] FIG. 8 shows .sup.15N.sub.2-.sup.1H HETCOR NMR spectra of (A): [(SiO).sub.xTaH.sub.y] of the present invention after reaction with .sup.15N.sub.2 and H.sub.2 at 100 C. for 10 hours and (B): [(SiO).sub.xTaH.sub.y] after reaction with .sup.15NH.sub.3 at room temperature.

[0039] FIG. 9 shows the IR difference spectra of [(SiO).sub.xTaH.sub.y] of the present invention before and after reaction with N.sub.2 and H.sub.2 and the IR spectral features associated with various vibrations possible upon reaction with N.sub.2 and H.sub.2 or NH.sub.3.

[0040] FIG. 10 shows a GC-MS chromatogram with corresponding SIM and M/Z pattern obtained from the gas phase analysis after reacting N.sub.2 and H.sub.2 in presence of [(SiO).sub.xTaH.sub.y] of the present invention.

[0041] FIG. 11 shows stepwise in-situ IR spectrums of the reaction of [(SiO).sub.xTaH.sub.y]] of the present invention pellet (Ta Wt. %: 7.39) as prepared and after treatment with .sup.14N.sub.2 (0.2 bar) and H.sub.2 (0.8 bar) at different temperatures ranging from room temperature to 100 C.

[0042] FIG. 12 shows dynamic reaction activities of [(SiO).sub.xTaH.sub.y] of the present invention on different supports for (a) NH.sub.3 formed vs. temperature and (b) TON vs. time.

[0043] FIG. 13 shows stepwise in-situ IR spectrums of the reaction of bimetallic [(SiO)TiH.sub.y] [(SiO).sub.xWH.sub.y] of the present invention with N.sub.2 and H.sub.2 at various temperatures.

[0044] FIG. 14 shows the stepwise in-situ IR spectrums of the reaction of [(SiO).sub.xZrH.sub.y] of the present invention with N.sub.2 and H.sub.2 at various temperatures.

[0045] FIG. 15 shows the stepwise in-situ IR spectrums of the reaction of [(SiO)xHfH.sub.y] of the present invention with N.sub.2 and H.sub.2 at various temperatures.

[0046] FIG. 16 shows the stepwise in-situ IR spectrums of the reaction of [(SiO).sub.xMoH.sub.y] of the present invention with N.sub.2 and H.sub.2 at various temperatures.

[0047] FIG. 17 shows the stepwise in-situ IR spectrums of the reaction of [(SiO).sub.xWH.sub.y] of the present invention with N.sub.2 and H.sub.2 at various temperatures.

DETAILED DESCRIPTION OF THE INVENTION

[0048] A discovery has been made that provides a solution to the aforementioned problems and inefficiencies associated with the generation of ammonia (NH.sub.3). The discovery is based on the reaction of nitrogen (N.sub.2) and hydrogen (H.sub.2) with a supported heterogeneous metal hydride complex under reaction conditions to produce ammonia. This discovery provides an elegant and economical alternative methodology to the current commercial processes (e.g., Haber-Bosch process).

[0049] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Metal Hydride Material

[0050] In one embodiment, the metal hydride material of the present invention has the general formula:

[(R).sub.xMH.sub.y]

where M is a transition metal; R is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0x; 1y; and x+y is equal to the valence of M. When R is an alkyl group, the alkyl group can be a straight or branched chain alkyl group having 1 to 20 carbon atoms. For example, the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secbutyl, tert-butyl, 1-pentyl, 2-pentyl, 3-pentyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 2,2-dimethyl-1-propyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 1-heptyl, 2-heptyl, 3-heptyl, 4-heptyl, 1-octyl, 2-octyl, 3-octyl, 4-octyl, 2-ethylhexyl, 1,1,3,3-tetramethylbutyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, cyclohexyl, cyclopentyl, or benzyl. When R is a substituted alkyl group, the substituted alkyl group can include any of the aforementioned alkyl groups that are additionally substituted with one or more heteroatom, such as a halogen (F, Cl, Br, I), boron, oxygen, nitrogen, sulfur, silicon, etc. Without limitation, a substituted alkyl group can include alkoxy, which means straight or branched chain alkoxy having 1 to 10 carbon atoms, and includes, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, secondary butoxy, tertiary butoxy, pentyloxy, isopentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy and decyloxy, haloalkyl, which means straight or alkyl having 1 to 8 carbon atoms which is substituted by at least one halogen, and includes, for example, chloromethyl, bromomethyl, fluoromethyl, iodomethyl, 2-chloroethyl, 2-bromoethyl, 2-fluoroethyl, 3-chloropropyl, 3-bromopropyl, 3-fluoropropyl, 4-chlorobutyl, 4-fluorobutyl, dichloromethyl, dibromomethyl, difluoromethyl, diiodomethyl, 2,2-dichloroethyl, 2,2-dibromoethyl, 2,2-difluoroethyl, 3,3-dichloropropyl, 3,3-difluoropropyl, 4,4-dichlorobutyl, 4,4-difluorobutyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 2,3,3-trifluoropropyl, 1,1,2,2-tetrafluoroethyl and 2,2,3,3-tetrafluoropropyl, or alkylamine, which includes mono- or di-substituted alkyl and/or substituted alkyl chains mentioned above attached to the nitrogen atom of the amine. In a preferred embodiment, R includes 1 to 7 carbon atoms, preferably 1 to 5. R can be a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, neopentyl, hexyl group, or combinations thereof. In certain embodiments, R can include a mixture of stereoisomers, such as enantiomers and diastereomers. When M is a transition metal, the transition metal can be a metal from Columns 4-12 of the Periodic Table. Non-limiting examples of transition metals include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, lanthanide series (e.g., La and Ce), actinide series, (e.g., Th). In a preferred embodiment, the transition metal is a Column 4-8 transition metal, such as Ta, Ti, Zr, Hf, Mo, or W, preferably Ta or Ti. Non-limiting commercial sources of transition metals include Sigma-Aldrich MO, USA.

[0051] In another embodiment, the metal hydride material can include a support. The support material or a carrier can be porous and have a high surface area. In some embodiments, the support is active (i.e., has catalytic activity). In other aspects, the support is inactive (i.e., non-catalytic). The support can be an inorganic oxide. In some embodiments, the support can include an inorganic oxide, alpha, beta or theta alumina (Al.sub.2O.sub.3), activated Al.sub.2O.sub.3, silicon dioxide (SiO.sub.2), titanium dioxide (TiO.sub.2), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), zirconium oxide (ZrO.sub.2), chromium oxides (CrO, CrO.sub.2, CrO.sub.3, CrO.sub.5, Cr.sub.2O.sub.3, or mixed valence species, such Cr.sub.8O.sub.2i), zinc oxide (ZnO), lithium aluminum oxide (LiAlO.sub.2), magnesium aluminum oxide (MgAlO.sub.4), manganese oxides (MnO, MnO.sub.2, Mn.sub.2O.sub.4), lantheum oxide (La.sub.2O.sub.3), activated carbon, silica gel, zeolites, activated clays, silicon carbide (SiC), diatomaceous earth, magnesia, aluminosilicates, calcium aluminate, carbon nanotubes (mono wall or multi walled), carbon black, sulfides, nitrides, mesoporus materials (i.e., MCM 41, SBA-15, and high surface area mesoporous supports), or combinations thereof. In certain aspects, the support can be mesoporous SiO.sub.2, fibrous SiO.sub.2 (KCC-1-700), binuclear dehydroxylated SiO.sub.2 (SiO.sub.2-700), mononuclear dehydroxylated SiO.sub.2, or any combination thereof. In other embodiments, the support material can include a carbonate (e.g., MgCO.sub.3, CaCO.sub.3, SrCO.sub.3, BaCO.sub.3, Y.sub.2(CO.sub.3).sub.3, La.sub.2(CO.sub.3).sub.3, or combination thereof).

[0052] The amount of metal hydride material on the support material depends, inter alia, on the catalytic activity of the catalyst. In some embodiments, the amount of metal hydride material present on the support ranges from 1 to 100 parts by weight of metal hydride material per 100 parts by weight of support, 0.5 to 50 parts by weight of metal hydride material per 100 parts by weight of support, from 1 to 30 parts by weight of metal hydride material per 100 parts by weight of support, from 1 to 20 parts by weight of metal hydride material per 100 parts by weight of support, or from 5 to 10 parts by weight of metal hydride material per 100 parts by weight of support. In other embodiments, the amount of metal hydride material present on the support is from 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, or 20 parts of metal hydride material per 100 parts by weight of support.

[0053] In some embodiments, the catalyst can be supported on a dehydroxylated silica material. The structure of the supported structure can include O-SupportH moieties, Support-O-MHR moieties, Support-O-MH moieties, or any combination thereof as shown in the representative structures below using SiO.sub.2 as the support material, where the squiggly line represents the surface of the support material. Although Si is shown it should be understood that other supports can produce these general active species.

##STR00005##

[0054] Non-limiting examples of a metal hydride supported on dehydroxlyated silica are Ta and Ti hydride supported materials. The supported Ta hydride material can have a general structure:

##STR00006##

where R.sub.1 and R.sub.2 are each individually a hydrogen, a hydrocarbon, a substituted hydrocarbon group, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof. When R.sub.1 and R.sub.2 are an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R.sub.1 and R.sub.2 are a substituted alkyl group, the substituted alkyl group can be any of the substituted alkyl groups previously mentioned. Preferably, R.sub.1 and R.sub.2 are each hydrogen. The supported Ti hydride material can have a general structure:

##STR00007##

[0055] The metal hydride material can include more than one hydride material or more than one metal. By way of example, the metal hydride can include a second metal hydride material having the general formula:

[(R.sub.2).sub.tM.sup.2H.sub.u]

where M.sup.2 is a transition metal with the proviso that M and M.sup.2 are different; R.sub.2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0t; 1u; and t+u is equal to the valence of M.sup.2. When R.sub.2 is an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R.sub.2 is a substituted alkyl group, the substituted alkyl group can be any of the substituted alkyl groups previously mentioned. Any of the described metal hydride materials of the current invention may also be in the form of a molecular complex, a molecular cluster, or a nanoparticle. The overall formula of the mixed hydride can be represented by [(R).sub.xMH.sub.y] [(R.sub.2).sub.tM.sup.2H.sub.u], where R, R.sub.2, M, M.sup.2, H.sub.y, and H.sub.u are defined above. Non-limiting examples of a bimetallic metal hydride material is a silica supported titanium tungsten hydride (e.g., [(R).sub.xSiH.sub.y]/SiO.sub.2 [(R.sub.2).sub.tWH.sub.u/SiO.sub.2]), which when treated with hydrogen can form [SiH.sub.y]/SiO.sub.2 [WH.sub.u/SiO.sub.2]).

B. Methods of Preparation

[0056] The materials used to make the unsupported and supported metal hydride materials of the present invention can be purchased or made by processes known to those of ordinary skill in the art (e.g., solution chemistry, schlenk filtration, precipitation/co-precipitation, sol-gel, templates/surface deriv ati zed synthesis, solid-state synthesis, microemul si on technique, solvothermal, sonochemical, etc.). In general aspects, unsupported and supported active metal hydride species (i.e. monometallic, bimetallic, or cluster hydrides) can be prepared by hydrogenating different precursors of transition metals (i.e., Columns 3-12 of the Periodic Table) containing various ligands, such as alkyl, alkylidyne, nitrides, hydrides, etc.

[0057] 1. Preparation of Metal Hydride Material

[0058] In one embodiment, a method to prepare the metal hydride material of the current invention is described. A first step of the method includes obtaining a solution comprising an hydrocarbon salt that include a hydrocarbon anion (R.sup.) and metal cation. The hydrocarbon anion (R.sup.) can be alkyl group or a substituted alkyl group including any of the alkyl groups or substituted alkyl groups previously mentioned. The cation can be lithium, sodium, potassium, magnesium, zinc, etc. Non-limiting examples of hydrocarbon salts include alkyllithium, alkylmagnesium halide, dialkylmagnesium, alkylzinc halide, dialkylzinc, etc., which can be purchased from a commercial source or prepared by known methods in the art under anhydrous conditions. In a non-limiting example, the hydrocarbon anion (R.sup.) is neopentyl lithium prepared by reacting neopentyl chloride and finely chopped Li wire in hexane. In step 2 of the method, the hydrocarbon anion (R.sup.) is reacted with a transition metal (M) precursor to form a hydrocarbon metal (R.sub.xM) material, where x is equal to the valence of M. In the reaction of a hydrocarbon anion (R.sup.) with a transition metal (M) precursor, leaving groups attached to the metal (M) precursor are displaced by the hydrocarbon anion (R.sup.) to form a carbon metal bond. The process can be highly exothermic so the reaction can be performed at low temperature or under cryogenic conditions. The leaving group attached to the metal precursor can be a charged or uncharged atom (or group of atoms) that can be displaced as a stable species. Examples of leaving groups include, but are not limited to, halogen (e.g., Cl, Br, I), azide (N.sub.3), thiocyanate (SCN), cyanate (CN), alkoxide (OR), acetate (OAc), trifluoroacetate (CO.sub.2CF.sub.3), amine (NR.sub.2), and sulfonate groups (e.g., OSO.sub.2R, wherein R can be a C.sub.1-10 alkyl group or a C.sub.6-14 aryl group each optionally substituted with 1-4 groups independently selected from a C.sub.1-10 alkyl group and an electronwithdrawing group) such as tosylate (toluenesulfonate, OTs), mesylate (methanesulfonate, OMs), brosylate (p-bromobenzenesulfonate, OBs), nosylate (4-nitrobenzenesulfonate, ONs), and triflate (trifluoromethanesulfonate, OTf). In a non-limited example, a solution of Ti(OEt).sub.4 in pentane was cooled to 78 C. in a dry ice/acetone bath and neopentyllithium in pentane was added. The reaction mixture was stirred for 1.5 hours at 78 C. and then warmed to room temperature and stirred for a further 3-6 hours. The pentane can then be removed to obtain crude tetraneopentyltitanium (TiNp.sub.4) as a brown solid which can be further purified by sublimation. In step 3 of the method, the R.sub.xM material is treated with hydrogen (H.sub.2) under conditions sufficient to form the catalyst having the general formula of:

[(R).sub.xMH.sub.y]

where M is a transition metal; R is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0x, 1y, and x+y is equal to the valence of M. When R is an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R is a substituted alkyl group, the substituted alkyl group can be any of the substituted alkyl groups previously mentioned. Step 4 includes drying the material of step 3. In a non-limiting example, a method to prepare the active metal hydride material includes treating the R.sub.xM material with hydrogen (H.sub.2). The exemplary method includes mixing anhydrous H.sub.2 and the unactivated metal hydride material and heating to 100-150 C. for 15 hours in a glass reactor tube in the dark to give the active metal hydride material that can be confirmed by spectrometric methods (e.g., NMR).

[0059] 2. Preparation of Supported Metal Hydride Material

[0060] In another embodiment, a method to prepare the supported metal hydride material of the current invention is described. In one aspect, the method includes first contacting R.sub.xM with a support material having active anionic sites prior to step 3 above. The support material can be silica, silica-Al.sub.2O.sub.3, partially dehydroxylated silica, mesoporous, microporous silicates, zeolites and other acidic/basic/amphoteric or porous/non-porous/amorphous/crystalline supports etc. The support material may contain an anchoring moiety or group that can bind with the metal directly or indirectly. Preferably the anchoring group is an anionic group containing hydroxyl, amine, carboxylate, thiol, etc. functionality. In a particular embodiment the support is dehydroxylated silica and R.sub.xM is grafted to the support material. In a non-limiting example, the method of grafting the R.sub.xM with a support material includes mixing R.sub.xM in a hydrocarbon solvent (e.g., pentane) with a support material (e.g. SiO.sub.2-(700)) at 25 C. and stirring for a desired amount of time (e.g., 2 hours) under an inert atmosphere to form the supported R.sub.xM material (e.g., [SiO-MR.sub.x]). The supported R.sub.xM material can be isolated from the solution using known separation methods (e.g., gravity filtration, centrifugation, vacuum filtration, etc.). After isolation, the solid can be washed with additional solvent (e.g. 1, 2, 3, 4, or 5 times with pentane) and dried under vacuum (e.g., 15 min under vacuum at 25 C.). The dried supported R.sub.xM material can then be hydrogenated as described in step 3 above to form the supported metal hydride catalyst.

[0061] In some aspects, the conditions of step 3 above where a R.sub.xM material or a supported R.sub.xM material (i.e. [SiO-MR.sub.x]) is treated with hydrogen (H.sub.2) under conditions sufficient to form an unsupported or supported active metal hydride catalyst can include a temperature of 60 C. to 160 C. and all temperatures there between (e.g., 61 C., 62 C., 63 C., 64 C., 65 C., 66 C., 67 C., 68 C., 69 C., 70 C., 71 C., 72 C., 73 C., 74 C., 75 C., 76 C., 77 C., 78 C., 79 C., 80 C., 81 C., 82 C., 83 C., 84 C., 85 C., 86 C., 87 C., 88 C., 90 C., 91 C., 92 C., 93 C., 94 C., 95 C., 96 C., 97 C., 98 C., 99 C., 100 C., 101 C., 102 C., 103 C., 104 C., 105 C., 106 C., 107 C., 108 C., 109 C., 110 C., 111 C., 112 C., 113 C., 114 C., 115 C., 116 C., 117 C., 118 C., 119 C., 120 C., 121 C., 122 C., 123 C., 124 C., 125 C., 126 C., 127 C., 128 C., 129 C., 130 C., 131 C., 132 C., 133 C., 134 C., 135 C., 136 C., 137 C., 138 C., 139 C., 140 C., 141 C., 142 C., 143 C., 144 C., 145 C., 146 C., 147 C., 148 C., 149 C., 150 C., 151 C., 152 C., 153 C., 154 C., 155 C., 156 C., 157 C., 158 C., or 159 C.), preferably 70 C. to 150 C. and a hydrogen pressure of 0.05 MPa to 0.1 MPa and all pressures there between (e.g., 0.06 MPa, 0.07 MPa, 0.08 MPa, or 0.09 MPa), preferably 0.08 MPa. In some embodiments, steps 1 through 4 are performed in the absence of light, or substantially no light, to inhibit photodegradation or photoactivation of the material. In a non-limiting example, a method to prepare the supported active metal hydride material includes mixing anhydrous H.sub.2 and the supported unactivated metal hydride material and heating to 100-150 C. at a pressure of 0.08 MPa for 15 hours in the dark to give the active metal hydride material that can be confirmed by spectrometric methods (e.g., NMR).

[0062] 3. Preparation of Bimetallic Hydride Material

[0063] In other aspects, the method can further include: (i) obtaining a [(R.sub.2).sub.tM.sup.2H.sub.u] material, where M.sup.2 is a transition metal, R.sub.2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0t, 1u, and t+u is equal to the valence of M.sup.2; and (ii) adding the material of step (i) to the compound of step (d). When R.sub.2 is an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R.sub.2 is a substituted alkyl group, the substituted alkyl group can be any of the substituted alkyl groups previously mentioned. The material of step (i) can be unsupported or supported. The metal hydride material can be a mixed with other unsupported and/or supported metal hydrides to form bimetallic or trimetallic metals with different transition metals in the form of a molecular complex, a molecular cluster or a nanoparticle. All combinations of mixtures of the unsupported and supported R.sub.xM, R.sub.xM.sup.2, [(R).sub.xMH.sub.y], and [(R.sub.2).sub.tM.sup.2H.sub.u]s are envisioned in the current embodiments. The supported and unsupported metals included in a bimetallic hydride material can be hydrogenated separately then combined or combined then hydrogenated together. Optionally, only one of the metals included in the bimetallic hydride material can be active and the mixture can be optionally further hydrogenated. For example, R.sub.xM or the dried solid powder obtained from the product of R.sub.xM grafted with a supported metal material (e.g. [SiO-MR.sub.x]) can be mixed with [(R.sub.2).sub.tM.sup.2H.sub.u] in having a certain metal (M.sup.2/M) ratio and hydrogenated. The ratio of metals in the bimetallic metal hydride material (i.e., M.sup.2/M or M/M.sup.2) can be 0.05:1, 0.1:1, o.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1:1. Preferably the ratio of metals is 1:1, 1:0.6 or 06:1. In a non-limiting example, [(SiO).sub.xM.sup.2H.sub.z] can be mixed with [(SiO).sub.xMH.sub.y] in pentane in 0.6:1 metal (M.sup.2/M) ratio. The powder obtained can then be hydrogenated under a H.sub.2 contianing atmosphere at 100 C. for a desired amount of time (e.g., 15 hours) to obtain the corresponding bimetallic active hydride material (e.g., [(SiO).sub.xMH.sub.y][(SiO).sub.xM.sup.2H.sub.z].

[0064] The methods or the processes described herein can be carried out in solution using suitable solvents which can be readily selected by one skilled in the art of organic synthesis. Suitable solvents typically are substantially nonreactive with the reactants, intermediates, and/or products at the temperatures at which the reactions are carried out, e.g., temperatures that can range from the solvent's freezing temperature to the solvent's boiling temperature. A given reaction can be carried out in one solvent or a mixture of more than one solvent. Depending on the particular reaction step, suitable solvents for a particular reaction step can be selected. Examples of common organic solvents include petroleum ethers; acetonitrile; aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; ketones such as acetone, and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, bis(2-methoxyethyl)ether, diethyl ether, di-isopropyl ether, and t-butyl methyl ether; alcohols such as methanol, ethanol, butanol, and isopropyl alcohol; aliphatic hydrocarbons such as pentane, hexanes, heptane; esters such as methyl acetate, ethyl acetate, methyl formate, ethyl formate, isopropyl acetate, and butyl acetate; amides such as dimethylformamide and dimethylacetamide; sulfoxides such as dimethylsulfoxide; halogenated aliphatic and aromatic hydrocarbons such as dichloromethane, chloroform, ethylene chloride, chlorobenzene, dichlorobenzene, and trichlorobenzene; and cyclic solvents such as cyclopentanone, cyclohexanone, and 2-methypyrrolidone.

[0065] The methods or processes described herein can be monitored according to any suitable method known in the art. For example, product formation can be monitored by spectroscopic means, such as nuclear magnetic resonance spectroscopy (NMR, e.g., .sup.1H or .sup.13C), infrared spectroscopy (IR), spectrophotometry (e.g., in-situ FT-IR or UV-visible), mass spectrometry (MS), or by chromatography such as high pressure liquid chromatograpy (HPLC), gas chromatography (GC), gel-permeation chromatography (GPC), or thin layer chromatography (TLC).

C. Process to Make Ammonia

[0066] In yet another embodiment, the metal hydride material of the current invention is capable of catalyzing the production of ammonia from nitrogen (N.sub.2) and hydrogen (H.sub.2). In one aspect, the metal hydride material capable of catalyzing the production of ammonia includes a support, preferably, dehydroxylated SiO.sub.2. Referring to FIG. 1, a method and system to prepare ammonia is described. In system 10, metal hydride material (e.g., [(R).sub.xMH.sub.y]) and optional solvents can be provided to a reactor unit 12 via solids inlet 14. Nitrogen (N.sub.2) and hydrogen (H.sub.2) and optional inert gases (e.g. argon) can be provided to reactor 12 via gas inlet 16. Although not shown, the reactor may have additional inlets for the introduction of gases that can be added to the reactor as mixtures or added separately and mixed within the reactor. In another aspect, the reaction can be carried out in a sealed reactor under inert atmosphere. The reactor can be made of materials that are chemically resistant to the reactants and products. The design and size of the reactor is sufficient to withstand the temperatures and pressures of the reaction. The reactor can include various automated and/or manual controllers, valves, heat exchangers, gauges, etc., for the operation of the reactor. The reactor can have insulation and/or heat exchangers to heat or cool the reactor as desired. Non-limiting examples of a heating/cooling source can be a temperature controlled furnace or an external, electrical heating block, heating coils, or a heat exchanger.

[0067] The reaction can be performed under inert conditions such that the concentration of oxygen (O.sub.2) gas in the reaction is low or virtually absent in the reaction such that O.sub.2 has a negligible effect on reaction performance (i.e. conversion, yield, efficiency, etc.). By way of example, gas inlet 26 may also be used for an evacuation outlet to remove and replace the atmosphere within the reactor with inert atmosphere or reactant gases in pump/purge cycles. Gas lines can be purged using dry N.sub.2 to remove any traces of air and moisture. Reactant gases, N.sub.2 and H.sub.2 in the desired ratio (e.g. 1:3) can be provided to reactor 12 via inlet 16 the total flow maintained at a suitable rate.

[0068] In reactor 12, contact of the nitrogen and hydrogen with the catalyst of the present invention produces ammonia. Conditions sufficient to produce ammonia include temperature, time, and pressure. Specifically, the production of ammonia from nitrogen (N.sub.2) and hydrogen (H.sub.2) includes a temperature range from 15 C. to 260 C. or greater than, equal to, or between any two of 15 C., 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., 90 C., 100 C., 110 C., 120 C., 130 C., 140 C., 150 C., 160 C., 170 C., 180 C., 190 C., 200 C., 210 C., 220 C., 230 C., 240 C., 250 C., and 260 C.). Preferably the reaction temperature is 100 C. to 200 C., preferably 150 C. The production of ammonia from N.sub.2 and H.sub.2 includes an average pressure from atmospheric, or 0.1 MPa to 2 MPa and all ranges and pressures there between (e.g., 0.2 MPa, 0.3 MPa, 0.4 MPA, 0.5 MPa, 0.6 MPa. 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, or 1.9 MPa). Preferably the reaction pressure is 1 MPa to 2 MPa, preferably 1.5 MPa. The upper limit on temperature and/or pressure can be determined by the reactor used. The reaction conditions may be further varied based on the type of the reactor used. The reactants can be heated for a time sufficient to produce a desired amount of ammonia. The time of reaction can be controlled by reactant supply or catalyst activity (e.g., TON). By way of example, the reaction time range can be at least 1 hour, at least 6 hours, at least 200 hours, at least 500 hours or until the catalyst is considered deactivated (e.g., ammonia is not produced in sufficient amount or is not produced).

[0069] An ammonia containing stream can be removed from reactor 12 via outlet 18. The reaction can be monitored by removing a portion of the ammonia stream and providing the removed portion to an acid trap containing a solution of H.sub.2SO.sub.4. NH.sub.3 formed from the reaction can be trapped in the acid and quantitative estimation of NH.sub.3 being formed can be done by volumetric titration of the definite amount of acid withdrawn from the trap over a period of time. In other embodiments of the process, the metal hydride material of the present invention can have a turnover rate number (TON) of at least 1, at least 50, at least 100. In a non-limiting examples, the TON in the presence of a supported titanium hydride material (1.29 wt. % Ti) with a N.sub.2:H.sub.2=1:3 for a reaction time of 10 hours, the TON can be 7.2 at 50 C. with 1.9 mmols/g of NH.sub.3 in the gas phase; 12.6 at 100 C. with 3.4 mmols/g of NH.sub.3 in the gas phase; and 16.2 at 250 C. with 4.4 mmols/g of NH.sub.3 in the gas phase.

[0070] The resulting ammonia produced from the processes of the current invention can be highly pure. However, if necessary, the resulting ammonia can be further purified and/or dried using common liquid or gas purification and/or drying techniques, such as fractional freezing (freezing distillation). The process can further include storing the directly produced or subsequently purified and/or dried ammonia.

[0071] A. D. Reactants and Products

[0072] Nitrogen (N.sub.2) gas and hydrogen (H.sub.2) gas can be obtained from various sources. In one non-limiting instance, the N.sub.2 gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (i.e., pressurized reverse osmosis membrane or pressure swing adsorption). N.sub.2 gas can also be obtained from a N.sub.2 gas generator using membranes or PSA which are typically more cost and energy efficient than bulk delivered nitrogen. N.sub.2 gas may also be obtained as a byproduct of air processing for industrial concentration of oxygen for steelmaking and other purposes. Without limitation N.sub.2, gas for use in the current invention may be supplied in compressed cylinders as OFN (oxygen-free nitrogen). The hydrogen may be from various sources, including streams coming from other chemical processes, like water splitting (e.g., photocatalysis, electrolysis, or the like), syngas production, ethane cracking, methanol synthesis, or conversion of methane to aromatics. When a mixture of gas is used, such as a mixture of N.sub.2 and H.sub.2, the gas can be premixed or mixed when added separately to the reactor. When the reactor contains a mixture of N.sub.2 and H.sub.2, the volume ratio of N.sub.2 to H.sub.2 (N.sub.2:H.sub.2) can be 1:1 to 1:4 and all ranges in ratios there between (e.g., 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, or 1:3.9), preferably 1:3. In some examples, the remainder of the reactant gas can include another gas or gases provided the gas or gases are inert, such as argon (Ar), further provided that they do not negatively affect the reaction. Preferably, the reactant mixture is highly pure (e.g., Grade 6 purity) and substantially devoid of water and oxygen. In some embodiments, the N.sub.2 and/or H.sub.2 can be dried prior to use (e.g., pass through a drying media) or contain a minimal amount of water or no water at all. Water can be removed from the reactant gases with any suitable method known in the art (e.g., condensation, liquid/gas separation, etc.). In some embodiments, the gases are passed through moisture and oxygen filters to remove moisture and oxygen to lower the water and oxygen content of the gases to a desired level, preferably, to level undetectable using known gas purity analysis methods.

[0073] The process of the present invention can produce a product stream of ammonia (NH.sub.3) that can be suitable as an intermediate or as feed material in a subsequent synthesis reactions to form a chemical product or a plurality of chemical products. In some embodiment, a portion of the ammonia is adorbed on the metal hydride material. Without being limited by theory, the produced NH.sub.3 can be collected and/or purified and stored or sold, and/or used in other processes (e.g., fertilizer manufacturing, nitric acid manufacture, metal treating operations, metal extraction, water and wastewater treament, stac emission control systems, photochemical processes, industrial refergeration systems, pulp and paper processes, rubber manufacture, chemical processes to produce leather and/or rubber, etc.).

EXAMPLES

[0074] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

Example 1

(Preparation of Neopentyl Lithium (LiCH.SUB.2.CMe.SUB.3.))

[0075] Neopentyl lithium was prepared by reacting neopentyl chloride (10 g) and finely chopped Li wire (3 g, 1% Na) in hexane according to Davidson et al., (Organomet. Chem. 1973, 57, 269) to afford 5-6 g of neopentyl lithium (70-80% yield).

Example 2

(Preparation of Tetraneopentyltitanium, TiNp.SUB.4 .or [Ti(CH.SUB.2.CMe.SUB.3.).SUB.4.])

[0076] To a solution of neopentyllithium in pentane (50 mL of a 0.65 M solution, 32.5 mmol) was added Ti(OEt).sub.4 (1.5 mL, 7.3 mmol) in pentane (20 mL). The reaction mixture was stirred for 1.5 h at 78 C. and then for 6 h at room temperature. The solvent was then removed to obtain the brown solid which was purified by sublimation (55 C., 10.sup.3 Torr) over 10 h to give the product according to Clark et al., J. Am. Chem. Soc., 1978, 100, 6774 and McCullough et al., J. Am. Chem. Soc., 1985, 107, 5987.

Example 3

(Preparation of Active Complex Hydride [(SiO).SUB.x.TiH.SUB.y.])

[0077] A mixture of Ti(Np).sub.4/[Ti(CH.sub.2CMe.sub.3).sub.4] (0.1 g, 0.3 mmol) in pentane (10 ml) and SiO.sub.2-(700, SiOH) (1 g, 0.3 mmol of SiOH) was stirred at 25 C. for 3 h in a double schlenk with a small pore silica frit. After filtration the solid was washed three times with pentane and dried for 15 min under vacuum at 25 C. to produce surface complex (SiO)TiNp.sub.3. FIG. 2 is a reaction schematic showing the preparation of the surface complex and the catalysis of ammonia production from nitrogen and hydrogen gases. Referring to FIG. 2, SiOH 22 is reacted with Ti(Np).sub.4 to form surface complex 24 ((SiO)TiNp.sub.3). Surface complex 24 is treated with hydrogen gas to form supported metal hydride 26 of the present invention. Supported metal hydride 26 can be reacted with N.sub.2 and H.sub.2 under conditions suitable to produce ammonia gas and absorbed ammonia on the surface support

[0078] Anhydrous H.sub.2 (1 bar) and the surface complex (SiO)TiNp.sub.3 (0.3 g, 0.056 mmol of metal) were heated at 100-150 C. for 15 h in a glass reactor (480 ml) in the dark to give [(SiO).sub.xTiH.sub.y]. The active catalysts were characterized. FIG. 3 shows the NMR spectra of [(SiO)TiH.sub.y]. Weak signals around 14.1 and 8.9 ppm correspond to the different TiH.sub.x species. Signals corresponding to Si-Hx and SiOH could be seen around 4.5 ppm and 2.2 ppm respectively. An intense signal around 0.96 ppm corresponds to residual alkyls remaining on the surface after hydrogenation. Elemental analysis of [(SiO).sub.xTiH.sub.y] showed around 0.54% C; 0.17% H and 1.29% Ti.

Example 4

(Preparation of Tetraneopentylzirconium: ZrNp.SUB.4 .or [Zr(CH.SUB.2.CMe.SUB.3.).SUB.4.])

[0079] Molecular precursor ZrNp.sub.4 was prepared according to Cheon et al., J. Am. Chem. Soc., 1997, 119, 6804-6813 with 4.35 g of ZrC1.sub.4 (18.65 mmol) and 57 ml of NpMgCl at 1.46 M (84 mmol, 4.5 equiv.). The white solid was purified by sublimation to afford ZrNp.sub.4 in 70% yield.

Example 5

(Preparation of Tetraneopentylhafnium: HfNp.SUB.4 .or [Hf(CH.SUB.2.CMe.SUB.3.).SUB.4.])

[0080] Molecular precursor HfNp.sub.4 was prepared according to Saint-Arroman et al., Applied Catalysis A: General, 290 (2005) 181-190; Davidson et al., J. Organomet. Chem. 1973, 57, 269 with 2.5 g of HfCl.sub.4 (7.79 mmol) and 10.5 ml of NpLi at 3.12 M (32.72 mmol, 4.2 equiv.) at 0 C. in hexane. The white solid obtained was purified by sublimation in 60% yield.

Example 6

(Preparation of Mo(CCMe.SUB.3.)(CH.SUB.2.CMe.SUB.3.).SUB.3.)

[0081] Molecular precursor Mo(CCMe.sub.3)(CH.sub.2CMe.sub.3).sub.3 was prepared by the reaction of molybdenum oxo chloride with neopentyl magnesium chloride in the ratio 1:6 using hexane/ether as the solvent at temperatures starting from 70 C. to 25 C. for around 5 hours according to Davidson et al.

Example 7

(Preparation of Hexamethyltungsten W(CH.SUB.3.).SUB.6.)

[0082] Molecular precursor W(CH.sub.3).sub.6 was prepared from WC1.sub.6 and (CH.sub.3).sub.2Zn according to McCullough et al.; Samantaray et al., J. Am. Chem. Soc., 2013, 3, 136. To WCl.sub.6 (1.80 g, 4.5 mmol) in dichloromethane (25 mL) was added (CH.sub.3).sub.2Zn (13.6 mmol, 1.0 M in heptane) at 80 C. followed by warming the mixture to 35 C. and stirring at this temperature for another 30 min. After successive filtrations with pentane and removal of the solvent, W(CH.sub.3).sub.6 as a red solid was obtained (0.16 g, 12%).

Example 8

(Preparation of [SiOZrNp.SUB.3.] by grafting ZrNp.SUB.4 .onto SiO.SUB.2.-(700))

[0083] A mixture of ZrNp.sub.4 (0.125 g, 0.33 mmol, 1.3 equiv.) in pentane (15 ml) and SiO.sub.2-(700) (1.10 g, 0.26 mmol of SiOH) was stirred at 25 C. for 2 h in a double schlenk with a small pore silica frit. After filtration the solid was washed three times with pentane and dried for 15 min under vacuum at 25 C.

Example 9

(Preparation of [SiOHfNp.SUB.3.] by Grafting HfNp.SUB.4 .onto SiO.SUB.2.-(700))

[0084] A mixture of HfNp.sub.4 (0.30 g, 0.65 mmol, 1.4 equiv.) in pentane (15 ml) and SiO.sub.2-(700) (2.0 g, 0.46 mmol of SiOH) was stirred at 25 C. for 2 h in a double schlenk with a small pore silica frit. After filtration the solid was washed three times with pentane and dried for 15 min under vacuum at 25 C.

Example 10

(Preparation of [SiOW(CH.SUB.3.).SUB.5.] by grafting W(CH.SUB.3.).SUB.6 .onto SiO.SUB.2.-(700))

[0085] Grafting of W(CH.sub.3).sub.6 was realized by stirring a mixture of an excess of [(SiO).sub.xTiH.sub.y] and silica which had been partially dehydroxylated at 700 C. (i.e., SiO.sub.2-700, which contains 0.30.1 mmol of silanol groups/g) at 50 C. under an inert atmosphere of argon. After several washing cycles with pentane and drying under high vacuum, yellowish white powder was formed.

Example 11

(Preparation of [SiOW(CH.SUB.3.).SUB.5.] by grafting W(CH.SUB.3.).SUB.6 .onto SiO.SUB.2.-(700))

[0086] Grafting of W(CH.sub.3).sub.6 was realized by stirring a mixture of an excess of [(SiO).sub.xTiH.sub.y] and silica which had been partially dehydroxylated at 700 C. (i.e., SiO.sub.2-700, which contains 0.30.1 mmol of silanol groups/g) at 50 C. under an inert atmosphere of argon. After several washing cycles with pentane and drying under high vacuum, yellowish white powder was formed.

Example 12

(Preparation of [SiOZrNp.SUB.3.] by Grafting ZrNp.SUB.4 .onto SiO.SUB.2.-(700))

[0087] A mixture of ZrNp.sub.4 (0.125 g, 0.33 mmol, 1.3 equiv.) in pentane (15 ml) and SiO.sub.2-(700) (1.10 g, 0.26 mmol of SiOH) was stirred at 25 C. for 2 h in a double schlenk with a small pore silica frit. After filtration the solid was washed three times with pentane and dried for 15 min under vacuum at 25 C.

Example 13

(Preparation of [SiOHfNp.SUB.3.] by grafting HfNp.SUB.4 .onto SiO.SUB.2.-(700))

[0088] A mixture of HfNp.sub.4 (0.30 g, 0.65 mmol, 1.4 equiv.) in pentane (15 ml) and SiO.sub.2-(700) (2.0 g, 0.46 mmol of SiOH) was stirred at 25 C. for 2 h in a double schlenk with a small pore silica frit. After filtration the solid was washed three times with pentane and dried for 15 min under vacuum at 25 C.

Example 14

(Preparation of [SiOW(CH.SUB.3.).SUB.5.] by grafting W(CH.SUB.3.).SUB.6 .onto SiO.SUB.2.-(700))

[0089] Grafting of W(CH.sub.3).sub.6 was realized by stirring a mixture of an excess of 1 and silica which had been partially dehydroxylated at 700 C. (i.e., SiO.sub.2-700, which contains 0.30.1 mmol of silanol groups/g) at 50 C. under an inert atmosphere of argon. After several washing cycles with pentane and drying under high vacuum, yellowish white powder was formed.

Example 15

(Preparation of Active Complex Hydrides [(SiO).SUB.x.MH.SUB.y.] where M=Ti, Zr, Hf, W and Mo)

[0090] Typically, anhydrous H.sub.2 (1 bar) and the surface complex (SiO)M-Np.sub.3 (0.3 g, 0.056 mmol of metal) were heated at 150 C. for 15 h in a glass reactor tube (480 ml) in the dark to give [(SiO).sub.xMH.sub.y] and the gas phase was quantified by GC. In order to make [(SiO)xW-H.sub.y], [(SiO)W-Me.sub.y] was treated with H.sub.2 (0.8 bar) @ 70 C. for 6 hours.

Example 16

(Preparation of Active Bimetallic Complex Hydrides [(SiO).SUB.x.MH.SUB.y.][SiO).SUB.x.MH.SUB.z.] where M=Ti, and M=W)

[0091] After grafting W(CH.sub.3).sub.6 onto SiO.sub.2-700, the solvent was filtered and removed. The solid powder obtained was dried and [(SiO)TiNp.sub.3] in pentane was added in 0.6:1 metal (W/Ti) ratio. The yellowish powder obtained was then hydrogenated with 0.8 bar of H.sub.2 in 800 ml glass reactor @ 100 C. for 15 hours to afford the corresponding bimetallic hydride.

Example 17

Ammonia Production Using Catalysts of the Present InventionGeneral Methods

[0092] 1. In-Situ IR Monitoring in an IR Cell

[0093] A MH.sub.x sample (30 mg) was made into a pellet and placed in an IR cell maintained under controlled atmosphere. The IR cell was evacuated and the IR spectrum was recorded. A side chamber with an adaptor containing 0.6 bar of dry H.sub.2 was fitted to the IR cell. The IR cell was first filled with 0.2 bar of N.sub.2 followed by 0.6 bar of dry H.sub.2. Reaction progress was monitored by recording the IR spectra at different temperatures at definite intervals of time. Heat treatments in N.sub.2 and H.sub.2 at different temperatures such as 25 C., 50 C., 100 C. and 250 C. each for 10 hours were tested and the surface reactions were monitored.

[0094] 2. Reaction with N.sub.2 and H.sub.2 in a PID Dynamic Reactor

[0095] An active hydride complex (200 mg) was loaded into a stainless steel reactor of half inch diameter, which can be separated from ambient atmosphere. The reactor was then connected to a PID reaction chamber. Gas lines were first purged using dry N.sub.2 to remove any traces of air and moisture. Reactant gases, N.sub.2 and H.sub.2 in the ratio 1:3 were then flowed to the catalyst chamber and the total flow maintained was 4.2 ml/min. The outlet was connected to an acid trap maintained at 0 C. containing 10.sup.4 M solution of H.sub.2SO.sub.4. NH.sub.3 formed was trapped in the acid. Quantitative estimation of NH.sub.3 being formed was done by volumetric titration of the definite amount of acid withdrawn from the trap over a period of time. Dynamic reactions were done at different temperatures by a temperature ramp while allowing the reaction to proceed for 10 hours at specific temperatures such as 25 C., 50 C., 100 C. and 250 C.

Example 18

(Production of Ammonia Using [(SiO).SUB.x.TiH.SUB.y.] of the Present Invention)

[0096] Using [(SiO).sub.xTiH.sub.y] on silica (Aerosil) dehydroxylated at 700 C. (e.g., a sample prepared as described in Example 3), it was demonstrated that a catalytic process could be accomplished forming ammonia from N.sub.2 and H.sub.2 under ambient conditions and the TON observed varied from 6 at 50 C. to 16 at 250 C. with the temperature ramp at periodic intervals of 10 hours. Dynamic reaction activities of complex [(SiO).sub.xTiH.sub.y] are shown in Table 1. The amount of complex (200 mg) corresponded to 0.0539 mmols of Ti and mononuclear SiO.sub.2-700 was used as the support. From the TON, it was determined that catalytic conversion of N.sub.2 to NH.sub.3 occurred. Notably, the TON was almost 100 times the TON of active TaH.sub.y on SiO.sub.2-700 (TON=0.071). Without wishing to be bound by theory, it is believed that a tris hydride of Ti forms by hydrogenation of [SiOTiNp.sub.3, where represents the support] (See, FIG. 2) but, a more stable monohydride of Ti can predominant by hydride transfer resulting in the simultaneous generation of SiH/SiH.sub.2 which might also play a role in the process of N.sub.2 reduction.

[0097] FIG. 4 shows the IR features of [(SiO).sub.xTiH.sub.y] before, during and after reaction with N.sub.2 and H.sub.2 under the specific reaction conditions used. FIG. 4 shows the in-situ IR spectrums of the [(SiO).sub.xTiH.sub.y] before and after reaction with N.sub.2 and H.sub.2 at various temperatures. Starting hydride showed the TiH.sub.x stretching frequencies around 1715, 1686, 1659, 1642 & 1618 cm.sup.1 and SiH and SiH.sub.2 stretching frequencies are around 2262 cm.sup.1 and 2195 cm.sup.1. Among the many types (mono, bis and tris) of TiH.sub.x formed, some specific type of hydrides are highly active and it even reacts with the 5 ppm of N.sub.2 available inside the argon atmosphere of the glovebox at room temperature. Hence, the starting spectrum contained the chemisorbed NH.sub.3 peak around 3369 cm.sup.1. The IR cell was further filled with 0.2 bar of N.sub.2 at room temperature. Immediate coordination of N.sub.2 was observed and the corresponding new bands appeared around 2342, 2312 and 2280 cm.sup.1. After adding H.sub.2 and heating at 50 C., new bands corresponding to physisorbed NH.sub.3 appeared. The bands corresponding to chemisorbed and physisorbed ammonia include 3369, 3290 and 3179 cm.sup.1. Upon further heating in N.sub.2 and H.sub.2 at 100 C. and 250 C., TiH.sub.x bands diminished and the formation of more ammonia was observed.

[0098] Trace amounts of SiNH.sub.2 were detected around 1550 cm.sup.1 which might be formed because of the gas phase NH.sub.3 interaction with siloxane bridges as the reaction was under static conditions at higher temperatures. The release of the adsorbed NH.sub.3 above 150-250 C. suggests that the regeneration of TiH.sub.x sites could be possible. TiH.sub.x complex was much more active than the TaH.sub.x complex. NH.sub.3 formed at room temperature was strongly bound to Ti and the release of NH.sub.3 happens upon heating to 50 C. or above. Unlike TaH.sub.x (See, Example 19) no splitting of NH.sub.3 into Ti(NH.sub.2)(NH) was observed in the case of TiH.sub.x even after heating up to 250 C.

TABLE-US-00001 TABLE 1 Ti Reaction conditions Time of the NH.sub.3 in the gas (wt. %) N.sub.2:H.sub.2 Temp. ( C.) reaction (h) Phase (mmols/g) TON 1.29 1:3 25 0 0 0 1.29 1:3 25 10 0 0 1.29 1:3 50 10 1.9 7.2 1.29 1:3 100 10 3.4 12.6 1.29 1:3 250 10 4.4 16.2

Example 19

(Production of Ammonia Using [(SiO).SUB.x.TaH.SUB.y.] of the Present Invention)

[0099] Active TaHy complex on SiO.sub.2-700 was prepared from corresponding methyl precursors following the literature procedures (Chen et al., Organometallics 2014, 33, 1205-1211; Chen et al., J Am Chem Soc. 2015, 137(2), 588-591; and Schrock et al., J Am Chem Soc, 1974, 96, 5288-5290). FIG. 5 shows the reaction schematic 50 for the formation of [(SiO).sub.xTaH.sub.y]. TaCl.sub.5 52 is reacted with Zn(CH.sub.3).sub.2 to form TaCl.sub.2(CH.sub.3).sub.3 54 that is further reacted with LiCH.sub.3 and SiO.sub.2 to form [(SiOTa(CH.sub.3).sub.4] 56 that can be hydrogenated to form supported metal hydride of the present invention (e.g., [(SiO).sub.xTaH.sub.y]) 58. Without wishing to be bound by theory, it is believed that transition structure 60 may be formed during the hydrogenation reaction.

[0100] Tantalum hydride complexes on SiO.sub.2-700 showed the formation of ammonia at room temperature and atmospheric pressure. However, heating at temperatures above 100 C. resulted in the splitting of ammonia on this surface resulting in the formation of surface amido imido complex. FIG. 6 shows the .sup.1H NMR spectrum of [(SiO).sub.xTaH.sub.y]. The .sup.1H-MAS NMR spectrum of the corresponding sample displays a main signal at 1 ppm corresponding to residual TaCH.sub.3, as well as several peaks of weak intensity at 3.5 & 4.3 ppm corresponding to SiHx and 0.0 ppm corresponding to evolved gas phase CH.sub.4 or SiCH.sub.3. Signal corresponding to SiNH.sub.2/NH.sub.3 protons should be around 1.1 ppm and 2.3 ppm respectively which cannot be distinguished in the current spectrum because of the broad signal at 1.0 ppm.

[0101] FIG. 7 shows the .sup.15N-MAS NMR spectrum of [(SiO).sub.xTaH.sub.y] after treatment with .sup.15N.sub.2 and H.sub.2 at room temperature displays a broad signal ranging from 320 ppm to 400 ppm corresponding to chemisorbed and physisorbed ammonia and SiNH.sub.2. Among the two main signal around 372 ppm is assigned to physisorbed .sup.15NH.sub.3 and 384 ppm is assigned to SiNH.sub.2. FIG. 8 shows heteronuclear correlation (HETCOR) experiments of [(SiO).sub.xTaH.sub.3]. 2D spectrum (A) shows the .sup.15N.sub.2-1H HETCOR spectrum that heat treatment for 10 hours at temperatures above 100 C. resulted in the formation of TaNH.sub.2. 2D spectrum (B) shows the .sup.15N.sub.2-1H HETCOR spectrum of [(SiO).sub.xTaH.sub.y] after reaction with .sup.15NH.sub.3 at room temperature. Spectrum (B) also shows some amounts of TaNH.sub.2 in accordance with the literature reports that [(SiO).sub.xTaH.sub.y] can split NH.sub.3 at high concentrations, however this region was not shown in the HETCOR spectrum.

[0102] FIG. 9 shows the IR difference spectra corresponding to the [(SiO).sub.xTaH.sub.y] before and after reaction with N.sub.2 and H.sub.2. Chemisorbed and physisorbed ammonia was observed after reaction with N.sub.2 and H.sub.2 at room temperature. Some positive changes in the SiHx and SiOH signals were observed along with the disappearance of the TaHx signals. The table shown in FIG. 9 corresponds to the frequencies expected for chemisorbed and physisorbed ammonia. FIG. 10 depicts the GC-MS chromatogram showing the detected NH.sub.3 in the gas phase for the static reaction [(SiO).sub.xTaH.sub.y] with N.sub.2 and H.sub.2 is provided as an additional proof for the formation of NH.sub.3.

[0103] Hydrogenolysis of [(SiO).sub.xTaMe.sub.y] was carried out by the reaction with H.sub.2 (0.8 bar) at 150 C. for 15 hours to generate [(SiO)xTaHy]. FIG. 11 shows the reaction of [(SiO).sub.xTaH.sub.y] with N.sub.2 and H.sub.2 at room temperature up to 100 C. was monitored stepwise by IR spectroscopy. Starting (SiO).sub.xTaH.sub.y shows the bands corresponding to TaH stretching around 1830 cm.sup.1 and SiH stretching around 2270 and 2220 cm.sup.1. Some residual alkyl species still remained on the surface as shown by the CH stretching bands observed in the region around 3000 cm.sup.1. After reaction with N.sub.2 and H.sub.2 at room temperature, IR spectrum of [(SiO).sub.xTaH.sub.y] showed the appearance of the bands corresponding to ammonia at 3374, 3288 and 3175 cm.sup.1. Another band appeared around 1608 cm.sup.1 corresponds to the characteristic bending vibration of the gas phase ammonia. Bands corresponding to TaH.sub.x diminished upon the addition of nitrogen. A considerable increase in the bands corresponding to silanols and SiH also is visible. It could be due to the reaction of H.sub.2 generated in-situ with strained SiOSi bridges upon coordination of N.sub.2 to [(SiO).sub.xTaH.sub.y]. After heat treatment at 100 C. for 10 hours, splitting of ammonia was observed, which is indicated by the bands corresponding to TaNH.sub.2 and SiNH.sub.2.

[0104] FIG. 12 shows dynamic reaction activities of [(SiO).sub.xTaH.sub.y] obtained on various silica supports for (a) NH3 formed vs. temperature and (b) TON vs. time. The supports selected were either amorphous/crystalline/porous or nonporous. The supports used were Aerosil SiO.sub.2, SBA-15 and KCC-1. Three supports were dehydroxylated at 700 C. and then used for grafting. Among the three samples [(SiO).sub.xTaH.sub.y] on Aerosil SiO.sub.2-700 showed the highest activity, though over all activities were not as high compared to [(SiO).sub.xTiH.sub.y]. By varying the dehydroxylation temperature, loading and strain on the surface also varied. By using aerosil SiO.sub.2-1000 the activity improved four fold than that of SiO.sub.2-700, however a faster deactivation was dominant on this sample.

[0105] A dissociative mechanism was anticipated for the activation of nitrogen, initiated by the insertion of N.sub.2 to the M-H bond and subsequent hydrogenations of this diazenido species to hydrazido species. Involvement of SiHx in the mechanism was anticipated during this step will eventually help to release one molecule of NH.sub.3. Further H.sub.2 additions successively result in an imido or amido surface moiety that helps to release the second molecule of ammonia thus regenerating the hydride active species.

Example 20

(Production of Ammonia from Bimetallic Hydride Complex [(SiO).SUB.x.WH.SUB.y.][(SiO).SUB.x.TiH.SUB.y.] of the Present Invention)

[0106] FIG. 13 shows the in-situ IR analyses of the reaction of [(SiO).sub.xWH.sub.y][(SiO).sub.xTiH.sub.y] with N.sub.2 and H.sub.2 at various temperatures. Bimetallic complex had a Ti:W ratio around 1:0.6. Starting hydride spectrum shows the weak bands of WH.sub.y around 1978, 1955, 1929 cm.sup.1 and strong bands of TiH.sub.y at 1715, 1686, 1659, 1642 & 1618 cm.sup.1. This complex showed better activities starting from the room temperature reactions. Upon exposure to N.sub.2, band corresponding to the N.sub.2 coordinated to W could be seen at 2317, 2276 and 2237 cm.sup.1 and that of N.sub.2 coordinated to Ti at 2342, 2312 and 2280 cm.sup.1.Further heat treatments in presence of N.sub.2 and H.sub.2 resulted in enhanced activities resulting in more amount of adsorbed NH.sub.3. This bimetallic complex had similar/better activities than that of TiH.sub.y or WH.sub.y. There was no splitting of NH.sub.3 observed on this complex similar to that of TiH.sub.y. Presence of some adsorbed NH.sub.3 was observed even at 250 C. as WH.sub.y favors the formation of ammonia at high temperatures.

Example 21

Production of Ammonia from of Other Transition Metal Hydrides of the Present Invention

[0107] FIG. 14 shows the in-situ IR spectrums of the reaction of [(SiO).sub.xZrH.sub.y] with N.sub.2 and H.sub.2 at various temperatures. Elemental analysis of [(SiO).sub.xZrH.sub.y] showed 0.47% C and 0.12% H and 2.47% Zr. The starting hydride spectrum shows the intense bands of ZrH.sub.y around 1621 cm.sup.1. This complex did not show any bands corresponding to NH.sub.3 at room temperature. After reaction with N.sub.2 and H.sub.2 for 10 h at room temperature, chemisorbed NH.sub.3 was observed and further heating improved the activity. NH.sub.3 splitting was not observed in the case of ZrH.sub.y also. When N.sub.2 is introduced to the ZrH.sub.y pellet, coordination of N.sub.2 was observed at room temperature around 2338 cm.sup.1. Formation of ZrOH and SiOH was also observed when N.sub.2 was introduced to the IR cell. This could be due to the reaction of SiOZr bond with H.sub.2/H.sup. forming ZrOH. SiOH formation was also observed as in the case of Ta. Further heating to high temperature showed the simultaneous increase in the formation of ZrOH and SiOH. Preliminary analysis indicates the probable leaching/de-grafting of the surface complex. It is also to be noted that after 250 C. heat treatment in presence of N.sub.2 and H.sub.2, bands corresponding to SiH.sub.2 vanished completely whereas SiH concentration increased/remained same on the surface.

[0108] FIG. 15 shows the in-situ IR spectrums of the reaction of [(SiO).sub.xHfH.sub.y] with N.sub.2 and H.sub.2 at various temperatures. Elemental analysis of [(SiO).sub.xHfH.sub.y] showed 1.64% C and 0.36% H and 5.24% Hf. Starting hydride spectrum shows the bands of HfH.sub.x around 1690 cm.sup.1. This complex did not show any bands corresponding to NH.sub.3 at room temperature. After reaction with N.sub.2 and H.sub.2 for 10 h at room temperature, negligible amount of chemisorbed NH.sub.3 was observed and further heating did not improve the activity. NH.sub.3 splitting was not observed in the case of HfH.sub.x similar to the ZrH.sub.x. Weak bands of physisorbed and chemisorbed N.sub.2 could be seen around 2336 cm.sup.1 and 2167 cm.sup.1 upon exposure to nitrogen. Upon increasing the heat treatment temperatures leaching/de-grafting induces the formation of HfOH and SiOH similar to ZrH.sub.x.

[0109] FIG. 16 shows the in-situ IR spectrums of the reaction of [(SiO).sub.xMoH.sub.y] with N.sub.2 and H.sub.2 at various temperatures. Elemental analysis showed 2.45% of Mo. Starting hydride spectrum shows the bands of MoH.sub.y around 1882, 1869, 1848 cm.sup.1. [(SiO).sub.xMoH.sub.y] did not show any bands corresponding to NH.sub.3 at room temperature. Upon exposure to N.sub.2, band corresponding to the N.sub.2 coordinated to Mo could be seen at 2304, 2295 and 2198 cm.sup.1. Further heat treatments in presence of N.sub.2 and H.sub.2 did not result in the formation of appreciable amount of NH.sub.3, even at 250 C. However, very weak bands of physisorbed NH.sub.3 were observed at 250 C.

[0110] FIG. 17 shows the in-situ IR spectrums of the reaction of [(SiO).sub.xWH.sub.y] with N.sub.2 and H.sub.2 at various temperatures. Elemental analysis showed 4.39% of W in the hydride. Starting hydride spectrum shows the bands of WH.sub.x around 1978, 1955, 1929 cm.sup.1. This complex did not show any bands corresponding to NH.sub.3 at room temperature. Upon exposure to N.sub.2, band corresponding to the N.sub.2 coordinated to W could be seen at 2317, 2276 and 2237 cm.sup.1. Further heat treatments in presence of N.sub.2 and H.sub.2 resulted in the formation of comparatively negligible amount of NH.sub.3. However, the observed activities were better than that of MoH.sub.y. Table 2. Results for the ammonia formation activity on various transition metal complex hydride on different supports.

TABLE-US-00002 TABLE 2 Method of screening Dynamic In-Situ Complex reaction IR Observations TaH.sub.x/SiO.sub.2-700 yes yes Appreciable activity (Binuclear) TaH.sub.x/SiO.sub.2-700 yes yes Negligible activity (Mononuclear) TaH.sub.x/SiO.sub.2-1000 yes yes Good activity, fast deactivation TaH.sub.x/SBA yes yes Less active, adsorbed NH.sub.3 15-700 stablized on SBA TaH.sub.x/KCC-1-700 yes yes Moderately active TaH.sub.x/MgO-200 no no Hydride species were not present/detected TiH.sub.x/SiO.sub.2-700 yes yes Good activity, scope for regeneration ZrH.sub.x/SiO.sub.2-700 no yes Less active, active species leaching suspected HfH.sub.x/SiO.sub.2-700 no yes Less active, active species leaching suspected MoH.sub.x/SiO.sub.2-700 no yes Less active, active only at high temperature, N.sub.2 coordinates at RT WH.sub.x/SiO.sub.2-700 no yes Less active, active only at high temperature, N.sub.2 coordinates at RT TiW(H.sub.x)/ no yes Similar activity to TiH.sub.x/SiO.sub.2-700 SiO.sub.2-700