Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
1997-08-28
2001-11-20
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S350000, C502S351000, C502S355000, C502S306000, C502S326000, C502S327000, C502S304000, C065S017200, C501S012000, C501S039000
Reexamination Certificate
active
06319876
ABSTRACT:
The catalytical selectivity has been developed to an increasingly important touchstone for technical applications of new heterogeneous catalysts, in spite of the great technical progress in the heterogeneous catalysis. The limits of the technical selectivity of the present catalyst generation most probably have been reached in all of the important chemical manufacturing processes. Highly developed chemical reaction techniques and improvements of the catalysts by semi-empirical catalyst modification by means of additives, surface modification and optimization of the pore structure are state of the art in the development of chemical processes. Shape selectivity, a first step for substrate selectivity, is the base of success of the zeolites, which constitute the most important new generation of heterogeneous catalysts. Shape selectivity is understood to denote selectivity of the formation of a chemical product; such selectivity is due to the differently limited mobilities of the various product molecules in the pores of the catalyst. It is prerequisite that the diameter of the pores of the catalyst is only slightly larger than that of the product molecules. Thus, the formation of p-xylene will be achieved, for instance, by isomerization of xylene mixtures by means of the acidic H-ZSM-5 zeolites, since the p-xylene, due to its straight form, is capable of diffusing considerably faster in the narrow pore channels of the zeolite, than are the more bulky o-xylene and m-xylene (D. H. Olsen, W. O. Haag, ACS Symp. Ser. 248 (1984) 275). The shape selectivity of zeolites in a large number of different reactions (P. B. Venuto, Microporous Materials 2 (1994) 297) is attributed to their microporous channel system having pores in the size of molecules. Although the number of zeolite structures having associated pore sizes increases continuously, accurate tailoring of zeolites is limited by the following facts:
(i) The variation of pore sizes is not continuous but depends upon the available crystal tape and, therefore, can be realized only in an incremental manner.
(ii) Monomodal distributions of the pore sizes comprising pore diameters in the range of 0.8-1.2 nm are unknown.
(iii) The concentration and the incorporation of second elements in the zeolite structure is strongly limited.
While only quite a few elements, such as Ti, Al, P, V, can be isomorphously substituted in the silicate structure, the obtainable concentration will at best be up to 50% and often does not even go beyond 2-3%. Zeolites have already been used as selective heterogeneous catalysts for a great number of organic reactions (P. B. Venuto, Microporous Materials 2 (1994) 297).
We now have found that amorphous microporous mixed metal oxides having an extremely narrow distribution of the microporous and pore diameters in the range of 0.5-1 nm, function as shape selective catalysts in a manner similar to that of the crystalline zeolites. We have found that by using such catalysts t-butyl ether can be directly produced from n-alcohols and t butyl alcohol or isobutene. A formation of t-butyl ether will not be observed under homogeneous conditions. These materials also do faster catalyze the formation of epoxides by direct oxidation of olefins having 6 or less carbon atoms than the formation of epoxides of larger alkenes. The product composition by the hydrogenating crack test of Dean is comparable to the product distribution originating from catalysis with zeolites having large pores such as Y zeolites, zeolite &bgr; or SAPO. We have found that such catalytically active amorphous microporous mixed metal oxides can be produced according to a modified sol-gel process. Of special importance for this production is the fact that at least one of the metal components, preferably a Si, Ti, Al or Zr derivative, must be present in a liquid state or in solution, and that the polycondensation in the sol-gel process will not be performed under basic conditions. Thus, no membranes are produced; the produced gel will rather be dried immediately under mild conditions. By rheological examinations we have found that the sol-gel process, catalyzed under acid to neutral reaction conditions, starts with a linear polymerization in such a way that the viscosity in the developing gel being formed increases together with the elasticity. Now, if a gel thus obtained is dried slowly and baked at low heating rates, there will be formed a microporous glass in which the different metal oxides are mixed together on an atomic or almost atomic base, i.e. without a formation of domains of the particular metal oxides. This microporous glass is now ground to the desired grain size and represents the catalyst which is suitable to be used for the shape selective catalysis.
The invention relates to a process for manufacturing shape selective, catalytically active, amorphous, microporous mixed metal oxides by to the sol-gel process, said process being characterized in that at least two hydrolyzable, liquid or dissolved compounds of the elements titanium, silicon, aluminium, zirconium or cerium are dissolved consecutively in one another, the clear solution is agitated at a pH of from 0 to 7 under addition of aqueous acidic catalysts or under addition of fluoride ions to effect a linear polymerization or polycondensation, the obtained gel is gently dried by heating at 60 to 70° C., and is calcinated at temperatures of 120 to 800° C. by using low heating rates whereby a microporous amorphous glass is obtained.
The resulting microporous, amorphous (exhibiting a homogeneous distribution of the elements, i.e. a homogeneous glass—no particles) non-ceramic glasses consist of a matrix of mixed metal oxides, in which at least about 90% of the pores of the material have a diameter between 0.3 and 1.2 nm, of substantially the same pore size and a surface area of more than 50 m
2
/g.
Preferably, the hydrolyzable liquid or dissolved compounds are selected from the group consisting of SiO
2
, TiO
2
, zirconium oxide, cerium oxide, spinel, mullite, silicon carbide, silicon nitride and titanium nitride.
In a further embodiment the matrix of mixed metal oxides contains at least 50% per weight of at least one compound, of the elements titanium, silicon, aluminum, zirconium and cerium, and up to 50% of one or more metal oxides in an atomic distribution selected from the group of the metals of Mo, Sn, Zn, V, Mn, Fe, Co, Ni, As, Pb, Sb, Bi, Ru, Re, Cr, W, Nb, Hf, La, Ce, Gd, Ga, In, Tl, Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba.
Furthermore, the matrix of mixed metal oxides may additionally contain up to 5% per weight of at least one of the noble metals Pt, Rh, Ir, Os, Ag, Au, Cu, Ni, Pd, Co in highly dispersed form in a metallic or oxidized state.
Acids, particularly hydrochloric acid, are preferred as the acid catalysts.
The calcination temperature is preferably 250 to 500° C.
In a preferred embodiment, the hydrolyzable, soluble compounds are pure alkoxy, mixed alkoxy, alkoxyoxo or acetylacetonate derivatives of the selected metals or metal oxides.
Furthermore, the invention relates to microporous, amorphous, non-ceramic glasses consisting of a matrix of mixed metal oxides, in which at least circa 90% of the pores of the material have a diameter of between 0.3 to 1.2 nm and essentially the same pore size and a surface area of more than 50 m
2
/g.
Preferably, the matrix of mixed metal oxides consists of at least two of the oxides of titanium, silicon, aluminium, zirconium or cerium.
More particularly, the matrix of mixed metal oxides consists of at least two compounds selected from the group consisting of SiO
2
, TiO
2
, Al
2
O
3
, zirconium oxide, cerium oxide, spinel, mullite, silicon carbide, silicon nitride and titanium nitride.
In another embodiment, the matrix of metal oxides consists of at least 50% per weight of one of the compounds of the elements titanium, silicon, aluminum, zirconium or cerium, and up to 50 percent per weight of one or more of metal oxides in an atomic distribution, selected from the group of the metals consisting of of Mo, Sn, Zn, V, Mn, Fe, Co, Ni, As, Pb, S
Bell Mark L.
Hailey Patricia L.
Norris & McLaughlin & Marcus
Studiengesellschaft Kohle MBH
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