Enhanced dispersion of two-dimensional metal oxide surface species on silica using an alkali promoter
Improved catalysts including two-dimensional metal oxide species highly dispersed on a silica support are disclosed, as well methods of making and using such catalysts. The catalysts are substantially free of metal oxide nanoparticles. The higher than expected maximum dispersion densities are obtained in the catalysts by introducing dispersion-promoting sodium ions, and optionally, aluminum ions, onto the silica support. The improved catalysts may be used in a variety of chemical processes, including, without limitation, in dehydrogenation, oxidation, and metathesis reactions.
1. A heterogeneous catalyst comprising one or more two-dimensional metal oxide species dispersed on the surface of a silica support that further comprises ions of one or more alkali metals wherein the mole ratio of the alkali metal ions present to the metal atoms of the metal oxide present is less than 0.25/1, wherein the metal oxide is aluminum oxide or an oxide of a group 3, group 4, group 5, group 6 or group 7 metal other than molybdenum, and wherein the catalyst is substantially free of metal oxide nanoparticles.
2. The heterogeneous catalyst of claim 1 , wherein the one or more two-dimensional metal oxide species are monomeric species.
3. The heterogeneous catalyst of claim 1 , wherein the one or more two-dimensional metal oxide species exhibit tetrahedral geometry around the metal atoms.
4. The heterogeneous catalyst of claim 1 , wherein the metal oxide is an oxide of a group 5, group 6 or group 7 metal other than molybdenum.
5. The heterogeneous catalyst of claim 4 , wherein the metal oxide is an oxide of a group 5 or group 6 metal other than molybdenum.
6. The heterogeneous catalyst of claim 5 , wherein the metal oxide is an oxide of a group 5 metal.
7. The heterogeneous catalyst of claim 1 , wherein the metal oxide is selected from the group consisting of aluminum oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, tungsten oxide, rhenium oxide, titanium oxide, and mixtures thereof.
8. The heterogeneous catalyst of claim 7 , wherein if vanadium oxide is selected, it is dispersed on the surface of the silica support in the range of 3.2-10 V-atoms/nm 2 ; if niobium oxide is selected, it is dispersed on the surface of the silica support in the range of 1.2-6 Nb-atoms/nm 2 ; and if tantalum oxide is selected, it is dispersed on the surface of the silica support in the range of 1-6 Ta-atoms/nm 2 .
9. The heterogeneous catalyst of claim 1 , wherein the ions of one or more alkalai metals are sodium ions.
10. The heterogeneous catalyst of claim 9 , wherein the sodium ions are present in the silica support at a concentration of about 0.15-1.4 Na-ions/nm 2 .
11. The heterogeneous catalyst of claim 9 , wherein the sodium ions are present in the silica support at a concentration of about 0.3-1.0 Na-ions/nm 2 .
12. The heterogeneous catalyst of claim 9 , wherein the sodium ions are present in the silica support at a concentration of about 0.4-0.8 Na-ions/nm 2 .
13. The heterogeneous catalyst of claim 9 , wherein the sodium ions are present in the silica support at a concentration of about 0.6 Na-ions/nm 2 .
14. A method of making a desired chemical product, comprising contacting a liquid or gaseous reactant with the heterogeneous catalyst of claim 1 , whereby the desired chemical product is formed by a process catalyzed by the heterogeneous catalyst.
15. The method of claim 14 , wherein the liquid or gaseous reactant is an alkane, the process catalyzed by the heterogeneous catalyst is:
(a) oxidative dehydrogenation, and the desired chemical product is an olefin;
(b) non-oxidative dehydrogenation, and the desired chemical product is an olefin; or
(c) alkane oxidation, and the desired chemical product is an oxygenate.
16. The method of claim 14 , wherein the liquid or gaseous reactant comprises one or more olefins, the process catalyzed by the heterogeneous catalyst is olefin metathesis, and the desired chemical product comprises one or more olefins that are different than the olefins of which the liquid or gaseous reactant is comprised.
17. The method of claim 14 , wherein the liquid or gaseous reactant is a chlorocarbon, the process catalyzed by the heterogeneous catalyst is chlorocarbon degradation, and the desired chemical product comprise products of chlorocarbon degradation.
18. The method of claim 14 , wherein the liquid or gaseous reactant is glycerol, the process catalyzed by the heterogeneous catalyst is glycerol conversion, and the desired chemical product is acrolein.