Patent Application
20190185333
The invention generally concerns a process for producing ammonia (NH3). More particularly, the process includes contacting a gaseous feed mixture that includes nitrogen (N2) and hydrogen (H2) with a metal hydride material under reaction conditions sufficient to produce a NH3 containing product stream.
Nitrogen fixation in any form is essential for the production of many industrially important chemicals. Direct artificial nitrogen fixation to ammonia can be challenging as the dinitrogen triple bond is not easily activated for reduction. Commerical production of ammonia includes the Haber-Bosch process. This process uses a heterogeneous multipromoted iron (Fe) catalyst supported on Al2O3 under high temperatures (350-550° C.) and pressures (150-350 atm). Due to the extreme conditions of the process, a significant amount of energy is required to produce the present gross production of 108 tons of ammonia annually.
Homogeneous catalysis to produce ammonia has been investigated. By way of example, Schrock et al. Science 2003, 301, pp. 76-78 describes a Mo complex that can catalytically transform dinitrogen to ammonia with a turn-over-number (TON) of 6 under ambient conditions. This process suffers from practical utility due to the complexity of the process.
Cleavage of the dinitrogen bond to produce oraganometallic nitrogen complexes has been described. By way of example, Avenier et al. (Science 2007, 317, pp. 1056-1060) describes cleavage of N2 at 250° C. and atmospheric pressure by H2 on an isolated silica surface-supported organometallic hydride centers, leading to an organometallic amido imido complex. In yet another example, of dinitrogen cleavages, Jia et al. (Inorg. Chem. 2015, Vol. 54, pp. 11648-11659) describes the organometallic amino reaction products of organometallic hydride complexes with hydrazines. Neither of these references describe the production of ammonia from cleavage of N2.
In view of above problems associated with alternative means of producing NH3, new economical routes for the production of NH3 to meet growing global demands are needed.
A discovery has been made that provides a solution to the aforementioned problems and inefficiencies associated with production of ammonia (NH3). The discovery is premised on the use of a metal hydride material to catalyze the reaction of nitrogen gas (N2) with hydrogen gas (H2) under reactions conditions sufficient to form NH3. Specifically, the metal hydride material can be a heterogeneous active surface complex based on one or more transition metal (Columns 3-12 of the Period Table) hydrides grafted onto an oxide support, such as amorphous/crystalline silica (SiO2). Notably, the reaction proceeds at a temperature from 15° C. to 260° C., 100° C. to 200° C., preferably 150° C. and a reaction pressure of atmospheric, or 0.1 MPa to 2 MPa, 1.0 MPa to 2.0 MPa, preferably 1.5 MPa. Without wishing to be limited by theory, it is believed that the current metal hydride material prepared from alkyl/alkylidiene precursors of the corresponding transition metals provide an elegant and efficient process to prepare NH3. As illustrated in non-limiting embodiments and in the Examples, active surface metal hydride complexes based on titanium (Ti) and tantalum (Ta) supported on SiO2 show high activity and high TON in the current process under mild reaction conditions (e.g., room temperature and low pressure).
In one particular aspect of the present invention, there is described a process for producing ammonia (NH3). The process can include contacting a gaseous feed mixture containing nitrogen (N2) and hydrogen (H2) with a metal hydride material under reaction conditions sufficient to produce a product stream including NH3. The metal hydride material can have the general formula:
[(R)xMHy]
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; 0≤x; 1≤y; and x+y is equal to the valence of M. The reaction conditions of the process can include a temperature from 15° C. to 260° C., 100° C. to 200° C., preferably 150° C. and a reaction pressure of atmospheric, or 0.1 MPa to 2 Mpa, 1.0 MPa to 2.0 MPa, preferably 1.5 MPa. In one aspect, a volume ratio of N2 to H2 (N2:H2) in the process can be 1:1 to 1:4, preferably 1:3. In another aspect, the metal hydride material can include a support, and the support can inlcude silica (SiO2), alumina (Al2O3), magnesia (MgO), titania (TiO2), chromia (Cr2O3), zeolites, carbon nanotubes, carbon black, sulfides, nitrides, or combinations thereof. In some aspects, the support can be mesoporous SiO2, fibrous SiO2 (KCC-1-700), binuclear dehydroxylated SiO2 (SiO2-700), mononuclear dehydroxylated SiO2, or any combination thereof. In particular instances, R of the metal hydride material in the process of the present invention can include 1 to 7 carbon atoms, preferably 1 to 5. By way of example, 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 some aspects, the metal hydride transition metal can be 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), a metal from the lanthanide series, lanthanum (La), cerium (Ce), a metal of the actinide series, thaallium (Th), or any alloy thereof. In a preferred aspect, the transition metal can be Ta, Ti, Zr, Hf, Mo, or W, preferably Ta or Ti. In one embodiment, the transition metal can be a supported Ta hydride material having a general structure of:
where R1 and R2 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. In one aspect, R1 and R2 are each hydrogen. In another aspect, the catalyst can be a supported Ti hydride having the general structure:
In another embodiment, the metal hydride material further includes a second metal hydride material having the general formula:
[(R2)tM2Hu]
where M2 is a transition metal with the proviso that M and M2 are different; R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0≤t; 1≤u; and t+u is equal to the valence of M2. In some aspects, the metal hydride material can be in the form of a molecular complex, a molecular cluster, or a nanoparticle. In other aspects of the process, a portion of the ammonia can be adsorbed on the metal hydride material. In certain aspects, the process further includes collecting and storing the ammonia.
In another particular aspect of the present invention, there is described a metal hydride material capable of catalyzing the production of ammonia from nitrogen (N2) and hydrogen (H2), the metal hydride material having the general formula:
[(R)xMHy]
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 0≤x, 1≤y, and x+y is equal to the valence of M, wherein the metal hydride material is capable of catalyzing the production of ammonia from a mixture of nitrogen and hydrogen. In one aspect, the metal hydride material can include a support, preferably, dehydroxylated SiO2.
In yet another particular aspect, there is described a method for preparing any one of the metal hydride materials of the present invention. The method can include (a) obtaining a solution comprising an hydrocarbon anion (R−); (b) reacting R− with a transition metal (M) precursor to form a hydrocarbon metal (RxM) material, where x is equal to the valence of M; and (c) treating the RxM material with hydrogen (H2) under conditions sufficient to form the catalyst having the general formula of:
[(R)xMHy]
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 0≤x, 1≤y, and x+y is equal to the valence of M; and (d) drying the material of step (c). In one aspect, the method further includes contacting RxM with a support material prior to step (c). The support material may contain anchoring groups (i.e., hydroxyl, amine, etc.) that can bind to the metal (M). In some aspects, the conditions of step (c) can include a temperature of 60° C. to 160° C., preferably 70° C. to 150° C., and a hydrogen pressure of 0.05 MPa to 0.1 MPa, preferably 0.08 MPa. In other aspects, the method can further include: (i) obtaining a [(R2)tM2Hu] material, where M2 is a transition metal R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0≤t, 1≤u, and t+u is equal to the valence of M2; and (ii) adding the material of step (i) to the compound of step (d). The material of step (i) can be supported.
In the context of the present invention, 24 embodiments are described. Embodiment 1 is a process for producing ammonia (NH3) comprising contacting a gaseous feed mixture comprising nitrogen (N2) and hydrogen (H2) with a metal hydride material under reaction conditions sufficient to produce a product stream comprising NH3, the metal hydride material having the general formula: [(R)xMHy] 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; 0≤x; 1≤y; and x+y is equal to the valence of M. Embodiment 2 is the process of embodiment 1, wherein the reaction conditions comprise a temperature from 15° C. to 260° C., 100° C. to 200° C., preferably 150° C. Embodiment 3 is the process of any one of embodiments 1 to 2, wherein the reactions conditions comprise a pressure of atmospheric pressure or 0.1 MPa to 2 MPa, 1 MPa to 2 MPa, preferably 1.5 MPa. Embodiment 4 is the process of any one of embodiments 1 to 3, wherein a volume ratio of N2 to H2 (N2:H2) is 1:1 to 1:4, preferably 1:3. Embodiment 5 is the process of any one of embodiments 1 to 4, wherein the metal hydride material comprises a support. Embodiment 6 is the process of embodiment 5, wherein the support comprises silica (SiO2), alumina (Al2O3), magnesia (MgO), titania (TiO2), chromia (Cr2O3), zeolites, carbon nanotubes, carbon black, sulfides, nitrides, or combinations thereof. Embodiment 7 is the process of embodiment 6, wherein the support is mesoporous SiO2, fibrous SiO2 (KCC-1-700), binuclear dehydroxylated SiO2 (SiO2-700), mononuclear dehydroxylated SiO2, or any combination thereof. Embodiment 8 is the process of any one of embodiments 1 to 7, wherein R comprises 1 to 7 carbon atoms, preferably 1 to 5. Embodiment 9 is the process of embodiment 8, 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. Embodiment 10 is the process of any one of embodiments 1 to 9, 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. Embodiment 11 is the process of embodiment 10, wherein the transition metal is Ta, Ti, Zr, Hf, Mo, or W, preferably Ta or Ti. Embodiment 12 is the process of embodiment 11, wherein the transition metal is Ta, and metal hydride material has a general structure of:
where R1 and R2 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. Embodiment 13 is the process of embodiment 12, wherein R1 and R2 are each hydrogen. Embodiment 14 is the process of embodiment 11, where the transition metal is Ti, and the metal hydride material has the general structure:
Embodiment 15 is the process of any one of embodiments 1 to 14, wherein the metal hydride material further comprises a second metal hydride material having the general formula: [(R2)tM2Hu] where: M2 is a transition metal with the proviso that M and M2 are different; R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0≤t; 1≤u; and t+u is equal to the valence of M2. Embodiment 16 is the process of any one of embodiments 1 to 15, wherein the metal hydride material is in the form of a molecular complex, a molecular cluster, or a nanoparticle. Embodiment 17 is the process of any one of embodiments 1 to 16, wherein a portion of the ammonia is adsorbed on the metal hydride material. Embodiment 18 is the process of any one of embodiments 1 to 17, further comprising collecting the ammonia.
Embodiment 19 is a metal hydride material capable of catalyzing the production of ammonia from nitrogen (N2) and hydrogen (H2), the metal hydride material having the general formula: [(R)xMHy] 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 0≤x, 1≤y, and x+y is equal to the valence of M, wherein the metal hydride material is capable of catalyzing the production of ammonia from a mixture of nitrogen and hydrogen. Embodiment 20 is the metal hydride material of embodiment 19, wherein the metal hydride material comprises a support, preferably, dehydroxylated SiO2.
Embodiment 21 is a method for preparing any one of the metal hydride materials of any one of the embodiments 19 to 20, the method comprising: (a) obtaining a solution comprising an hydrocarbon anion (R−); (b) reacting W with a transition metal (M) precursor to form a hydrocarbon metal (RxM) material, where x is equal to the valence of M; and (c) treating the RxM material with hydrogen (H2) under conditions sufficient to form the catalyst having the general formula of: [(R)xMHy] 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 0≤x, 1≤y, and x+y is equal to the valence of M; and (d) drying the material of step (c). Embodiment 22 is the method of embodiment 21, further comprising contacting RxM with a support material prior to step (c). Embodiment 23 is the method of any one of embodiments 21 to 22, wherein the conditions of step (c) comprise a temperature of 60° C. to 160° C., preferably 70° C. to 150° C., and a hydrogen pressure of 0.05 MPa to 0.1 MPa, preferably 0.08 MPa. Embodiment 24 is the method of any one of embodiments 21 to 23, further comprising: (i) obtaining a [(R2)tM2Hu] material, where: M2 is a transition metal; R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0≤t, 1≤u, and t+u is equal to the valence of M2; and (ii) adding the material of step (i) to the compound of step (d). Embodiment 24 is the method of emboidmnet 24, wherein the material of step (i) is supported.
The following includes definitions of various terms and phrases used throughout this specification.
The term “homogeneous” in the context of this invention means the catalyst is soluble (i.e., same phase as the reactants) in the reaction solution. In direct contrast, the term “heterogeneous” refers to the form of catalysis where the phase of the catalyst differs from that of the reactants.
The term “alkyl group” refers to a straight or branched chain alkyl moiety having 1 to 20 carbon atoms and includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, 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-oetyl, 3-oetyl, 4-octyl, 2-ethylhexyl, 1,1,3,3-tetramethylbutyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, cyclohexyl, cyclopentyl, or benzyl.
The term “substituted alkyl group” means 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.
The term “catalyst” means a substance which alters the rate of a chemical reaction. “Catalytic” means having the properties of a catalyst.
The term “nanotube” means a tubular structure having at least one diameter on the order of nanometers (e.g., between about 1 and 1000 nanometers) and an aspect ratio preferably greater than 5:1. The “aspect ratio” of a nanotube is the ratio of the actual length (L) of the nantube to the diameter (D) of the nanotube.
“Nanoparticle” means a particle having at least one diameter on the order of nanometers (e.g., between about 1 and 1000 nanometers).
The “turn over number” or ON,” as used herein, means the number of moles of substrate that a mole of catalyst converts in the timeframe of the experiment or before being deactivated. TON is calculated as the number of moles of nitrogen (N2), divided by the number of moles of metal hydride material unless otherwise indicated.
The term “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.
The term “substantially” and its variations are defined to include to ranges within 10%, within 5%, within 1%, or within 0.5%.
The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.
The terms “wt. %”, “vol. %”, or “mol. %” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt. % of component.
The use of the words “a” or “an” when used in conjunction with any of the terms “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”
The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
The methods of the present invention can “comprise,” “consist essentially of,” or “consist of” particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase “consisting essentially of,” in one non-limiting aspect, a basic and novel characteristic of the methods and catalysts of the present invention are their abilities to producing NH3 from N2 and H2.
Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.
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.
A discovery has been made that provides a solution to the aforementioned problems and inefficiencies associated with the generation of ammonia (NH3). The discovery is based on the reaction of nitrogen (N2) and hydrogen (H2) 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).
These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.
In one embodiment, the metal hydride material of the present invention has the general formula:
[(R)xMHy]
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; 0≤x; 1≤y; 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.
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 (Al2O3), activated Al2O3, silicon dioxide (SiO2), titanium dioxide (TiO2), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), zirconium oxide (ZrO2), chromium oxides (CrO, CrO2, CrO3, CrO5, Cr2O3, or mixed valence species, such Cr8O2i), zinc oxide (ZnO), lithium aluminum oxide (LiAlO2), magnesium aluminum oxide (MgAlO4), manganese oxides (MnO, MnO2, Mn2O4), lantheum oxide (La2O3), 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 SiO2, fibrous SiO2 (KCC-1-700), binuclear dehydroxylated SiO2 (SiO2-700), mononuclear dehydroxylated SiO2, or any combination thereof. In other embodiments, the support material can include a carbonate (e.g., MgCO3, CaCO3, SrCO3, BaCO3, Y2(CO3)3, La2(CO3)3, or combination thereof).
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.
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 SiO2 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.
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:
where R1 and R2 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 R1 and R2 are an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R1 and R2 are a substituted alkyl group, the substituted alkyl group can be any of the substituted alkyl groups previously mentioned. Preferably, R1 and R2 are each hydrogen. The supported Ti hydride material can have a general structure:
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:
[(R2)tM2Hu]
where M2 is a transition metal with the proviso that M and M2 are different; R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; 0≤t; 1≤u; and t+u is equal to the valence of M2. When R2 is an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R2 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)xMHy] [(R2)tM2Hu], where R, R2, M, M2, Hy, and Hu are defined above. Non-limiting examples of a bimetallic metal hydride material is a silica supported titanium tungsten hydride (e.g., [(R)xSiHy]/SiO2 [(R2)tWHu/SiO2]), which when treated with hydrogen can form [≡SiHy]/SiO2 [WHu/SiO2]).
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.
1. Preparation of Metal Hydride Material
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−) and metal cation. The hydrocarbon anion (R−) 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−) 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−) is reacted with a transition metal (M) precursor to form a hydrocarbon metal (RxM) material, where x is equal to the valence of M. In the reaction of a hydrocarbon anion (R−) with a transition metal (M) precursor, leaving groups attached to the metal (M) precursor are displaced by the hydrocarbon anion (R−) 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 (N3), thiocyanate (SCN), cyanate (CN), alkoxide (OR), acetate (OAc), trifluoroacetate (CO2CF3), amine (NR2), and sulfonate groups (e.g., OSO2—R, wherein R can be a C1-10 alkyl group or a C6-14 aryl group each optionally substituted with 1-4 groups independently selected from a C1-10 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)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 (TiNp4) as a brown solid which can be further purified by sublimation. In step 3 of the method, the RxM material is treated with hydrogen (H2) under conditions sufficient to form the catalyst having the general formula of:
[(R)xMHy]
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 0≤x, 1≤y, 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 RxM material with hydrogen (H2). The exemplary method includes mixing anhydrous H2 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).
2. Preparation of Supported Metal Hydride Material
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 RxM with a support material having active anionic sites prior to step 3 above. The support material can be silica, silica-Al2O3, 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 RxM is grafted to the support material. In a non-limiting example, the method of grafting the RxM with a support material includes mixing RxM in a hydrocarbon solvent (e.g., pentane) with a support material (e.g. SiO2-(700)) at 25° C. and stirring for a desired amount of time (e.g., 2 hours) under an inert atmosphere to form the supported RxM material (e.g., [SiO-MRx]). The supported RxM 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 RxM material can then be hydrogenated as described in step 3 above to form the supported metal hydride catalyst.
In some aspects, the conditions of step 3 above where a RxM material or a supported RxM material (i.e. [≡SiO-MRx]) is treated with hydrogen (H2) 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 H2 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).
3. Preparation of Bimetallic Hydride Material
In other aspects, the method can further include: (i) obtaining a [(R2)tM2Hu] material, where M2 is a transition metal, R2 is a hydrocarbon, a substituted hydrocarbon, or any combination thereof, preferably, an alkyl group, a substituted alkyl group, or any combination thereof; and 0≤t, 1≤u, and t+u is equal to the valence of M2; and (ii) adding the material of step (i) to the compound of step (d). When R2 is an alkyl group, the alkyl group can be any of the alkyl groups previously mentioned. When R2 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 RxM, RxM2, [(R)xMHy], and [(R2)tM2Hu]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, RxM or the dried solid powder obtained from the product of RxM grafted with a supported metal material (e.g. [≡SiO-MRx]) can be mixed with [(R2)tM2Hu] in having a certain metal (M2/M) ratio and hydrogenated. The ratio of metals in the bimetallic metal hydride material (i.e., M2/M or M/M2) 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, [(≡Si—O)xM2Hz] can be mixed with [(≡Si—O)xMHy] in pentane in 0.6:1 metal (M2/M) ratio. The powder obtained can then be hydrogenated under a H2 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., [(≡Si—O)xMHy][(≡Si—O)xM2Hz].
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.
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., 1H or 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).
In yet another embodiment, the metal hydride material of the current invention is capable of catalyzing the production of ammonia from nitrogen (N2) and hydrogen (H2). In one aspect, the metal hydride material capable of catalyzing the production of ammonia includes a support, preferably, dehydroxylated SiO2. Referring to
The reaction can be performed under inert conditions such that the concentration of oxygen (O2) gas in the reaction is low or virtually absent in the reaction such that O2 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 N2 to remove any traces of air and moisture. Reactant gases, N2 and H2 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.
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 (N2) and hydrogen (H2) 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 N2 and H2 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).
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 H2SO4. NH3 formed from the reaction can be trapped in the acid and quantitative estimation of NH3 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 N2:H2=1:3 for a reaction time of 10 hours, the TON can be 7.2 at 50° C. with 1.9 mmols/g of NH3 in the gas phase; 12.6 at 100° C. with 3.4 mmols/g of NH3 in the gas phase; and 16.2 at 250° C. with 4.4 mmols/g of NH3 in the gas phase.
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.
A. D. Reactants and Products
Nitrogen (N2) gas and hydrogen (H2) gas can be obtained from various sources. In one non-limiting instance, the N2 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). N2 gas can also be obtained from a N2 gas generator using membranes or PSA which are typically more cost and energy efficient than bulk delivered nitrogen. N2 gas may also be obtained as a byproduct of air processing for industrial concentration of oxygen for steelmaking and other purposes. Without limitation N2, 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 N2 and H2, the gas can be premixed or mixed when added separately to the reactor. When the reactor contains a mixture of N2 and H2, the volume ratio of N2 to H2 (N2:H2) 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 N2 and/or H2 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.
The process of the present invention can produce a product stream of ammonia (NH3) 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 NH3 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.).
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.
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).
To a solution of neopentyllithium in pentane (50 mL of a 0.65 M solution, 32.5 mmol) was added Ti(OEt)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., 10−3 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.
A mixture of Ti(Np)4/[Ti(CH2CMe3)4] (0.1 g, 0.3 mmol) in pentane (10 ml) and SiO2-(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)Ti—Np3.
Anhydrous H2 (1 bar) and the surface complex (≡SiO)Ti—Np3 (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)xTiHy]. The active catalysts were characterized.
Molecular precursor ZrNp4 was prepared according to Cheon et al., J. Am. Chem. Soc., 1997, 119, 6804-6813 with 4.35 g of ZrC14 (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 ZrNp4 in 70% yield.
Molecular precursor HfNp4 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 HfCl4 (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.
Molecular precursor Mo(≡CCMe3)(CH2CMe3)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.
Molecular precursor W(CH3)6 was prepared from WC16 and (CH3)2Zn according to McCullough et al.; Samantaray et al., J. Am. Chem. Soc., 2013, 3, 136. To WCl6 (1.80 g, 4.5 mmol) in dichloromethane (25 mL) was added (CH3)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(CH3)6 as a red solid was obtained (0.16 g, 12%).
A mixture of ZrNp4 (0.125 g, 0.33 mmol, 1.3 equiv.) in pentane (15 ml) and SiO2-(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.
A mixture of HfNp4 (0.30 g, 0.65 mmol, 1.4 equiv.) in pentane (15 ml) and SiO2-(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.
Grafting of W(CH3)6 was realized by stirring a mixture of an excess of [(≡Si—O)xTiHy] and silica which had been partially dehydroxylated at 700° C. (i.e., SiO2-700, which contains 0.3±0.1 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.
Grafting of W(CH3)6 was realized by stirring a mixture of an excess of [(≡Si—O)xTiHy] and silica which had been partially dehydroxylated at 700° C. (i.e., SiO2-700, which contains 0.3±0.1 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.
A mixture of ZrNp4 (0.125 g, 0.33 mmol, 1.3 equiv.) in pentane (15 ml) and SiO2-(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.
A mixture of HfNp4 (0.30 g, 0.65 mmol, 1.4 equiv.) in pentane (15 ml) and SiO2-(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.
Grafting of W(CH3)6 was realized by stirring a mixture of an excess of 1 and silica which had been partially dehydroxylated at 700° C. (i.e., SiO2-700, which contains 0.3±0.1 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.
Typically, anhydrous H2 (1 bar) and the surface complex (≡SiO)M-Np3 (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)xMHy] and the gas phase was quantified by GC. In order to make [(≡SiO)xW-Hy], [(≡SiO)W-Mey] was treated with H2 (0.8 bar) @ 70° C. for 6 hours.
After grafting W(CH3)6 onto SiO2-700, the solvent was filtered and removed. The solid powder obtained was dried and [(≡SiO)Ti—Np3] in pentane was added in 0.6:1 metal (W/Ti) ratio. The yellowish powder obtained was then hydrogenated with 0.8 bar of H2 in 800 ml glass reactor @ 100° C. for 15 hours to afford the corresponding bimetallic hydride.
1. In-Situ IR Monitoring in an IR Cell
A MHx 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 H2 was fitted to the IR cell. The IR cell was first filled with 0.2 bar of N2 followed by 0.6 bar of dry H2. Reaction progress was monitored by recording the IR spectra at different temperatures at definite intervals of time. Heat treatments in N2 and H2 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.
2. Reaction with N2 and H2 in a PID Dynamic Reactor
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 N2 to remove any traces of air and moisture. Reactant gases, N2 and H2 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 10−4 M solution of H2SO4. NH3 formed was trapped in the acid. Quantitative estimation of NH3 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.
Using [(≡Si—O)xTiHy] 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 N2 and H2 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 [(≡Si—O)xTiHy] are shown in Table 1. The amount of complex (200 mg) corresponded to 0.0539 mmols of Ti and mononuclear SiO2-700 was used as the support. From the TON, it was determined that catalytic conversion of N2 to NH3 occurred. Notably, the TON was almost 100 times the TON of active TaHy on SiO2-700 (TON=0.071). Without wishing to be bound by theory, it is believed that a tris hydride of Ti forms by hydrogenation of [≡Si—O—TiNp3, where ≡ represents the support] (See,
Trace amounts of Si—NH2 were detected around 1550 cm−1 which might be formed because of the gas phase NH3 interaction with siloxane bridges as the reaction was under static conditions at higher temperatures. The release of the adsorbed NH3 above 150-250° C. suggests that the regeneration of Ti—Hx sites could be possible. Ti—Hx complex was much more active than the TaHx complex. NH3 formed at room temperature was strongly bound to Ti and the release of NH3 happens upon heating to 50° C. or above. Unlike Ta—Hx (See, Example 19) no splitting of NH3 into Ti(NH2)(═NH) was observed in the case of Ti—Hx even after heating up to 250° C.
Active TaHy complex on SiO2-700 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).
Tantalum hydride complexes on SiO2-700 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.
Hydrogenolysis of [(≡SiO)xTaMey] was carried out by the reaction with H2 (0.8 bar) at 150° C. for 15 hours to generate [(≡SiO)xTaHy].
A dissociative mechanism was anticipated for the activation of nitrogen, initiated by the insertion of N2 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 NH3. Further H2 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.
This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/376,015 filed Aug. 17, 2016, which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/054866 | 8/9/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62376015 | Aug 2016 | US |
