High surface area sol-gel route prepared hydrogenation...

Details High surface area sol-gel route prepared hydrogenation... High surface area sol-gel route prepared hydrogenation...

2001-06-28

2004-02-03

Dentz, Bernard (Department: 1625)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S234000, C502S308000, C502S309000, C502S311000, C502S339000

Reexamination Certificate

active

06686310

ABSTRACT:

FIELD OF THE INVENTION
This invention concerns novel compositions, useful as catalysts, said compositions comprising metals and metal ions, such as ruthenium (Ru) and palladium (Pd), incorporated in an inorganic matrix comprising an inorganic oxide network. Catalyst activity is enhanced versus analogous supported metal catalysts.
TECHNICAL BACKGROUND
E. I. Ko, in the Handbook of Heterogeneous Catalysis, ed. by G. Ertl et al, reviews generally the use of sol-gel processes for the preparation of catalytic materials. There is no disclosure of nor suggestion of ruthenium or rhenium containing catalysts.
U.S. Pat. No. 4,622,310 discloses inorganic phosphate aerogels. The utility stated is as porous inert carrier materials (supports) in polymerization and copolymerization processes. Use of the inorganic phosphates as supports for elements in groups VIB, VIIB and VIII of the Periodic Table is described. There is no disclosure nor suggestion of incorporating the elements within the inorganic phosphate gel matrix.
U.S. Pat. No. 4,469,816 discloses a catalyst composition comprising a uniform dispersion of individual metallic palladium particles impregnated onto, within and throughout an alumina aerogel support processes for the preparation of catalytic materials. There is no disclosure of nor suggestion of ruthenium or rhenium containing catalysts.
U.S. Pat. No. 5,538,931 discloses a process for preparing a supported catalyst comprising a transition metal selected from palladium, platinum, nickel, cobalt or copper on an aerogel support.
DE-A 195 30 528 and DE-A 195 37 202 disclose catalysts comprising ruthenium dispersed in titania and zirconia sol-gel matrices, respectively. No promotors or co-calalysts are described.
SUMMARY OF THE INVENTION
This invention provides catalyst precursor compositions comprising catalytic species dispersed in and distributed throughout a high surface area matrix wherein, the catalytic species is selected from the group consisting of ruthenium and palladium, in the optional presence of a promoter selected from the group consisting of rhenium, molybdenum and tin.
The high surface area matrix material may be an inorganic oxide network, optionally prepared by the sol-gel route.
This invention further provides catalyst compositions comprising the reduced form of the above catalyst precursor compositions.
The catalyst precursor composition may further include a promoter.
Preferred promoters are selected from the group consisting of Rhenium, Molybdenum and Tin.
This invention further provides improved processes for the reduction of maleic acid to tetrahydrofuran (THF) and 1,4-butanediol (BDO) and for the reduction of gamma butyrolactone to tetrahydrofuran and 1,4-butanediol, the improvement consisting of the use of the catalysts of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention concerns novel catalyst compositions containing metals and metal ions, such as ruthenium (Ru) and palladium (Pd), incorporated into a matrix comprising inorganic oxides and oxyhydroxides of Ti, Nb, Ta, Zr and Si, Al, and others.
As used herein, the term matrix means a skeletal framework of oxides and oxyhydroxides derived from the hydrolysis and condensation of alkoxides and other reagents. The framework typically comprises 30% or more, by weight, of the total catalyst composition. As discussed below, porosity and microstructure can be controlled, in some cases, by synthetic parameters (i.e. pH, temperature), drying, and other heat conditioning. As used herein, the term microstructure means a description, both physical and chemical in nature, of the bonding of domains and crystallites with each other and their arrangement and physical appearance or morphology in a matrix or solid; this term also describes the structure and morphology, that is bonding and physical appearance, of the other active cationic precursors which are included in this invention.
The catalytic species are dispersed in and distributed throughout a high surface area matrix. Alternatively, the catalytic species may be referred to as being “matrix incorporated”.
Certain promoter materials, for example rhenium (Re), molybdenum (Mo) and tin (Sn), may also be present. Typical preparations involve sol gel chemistry. It is understood that sol gel products can be typically incompletely condensed resulting in products bearing residual hydroxy or alkoxy groups.
The catalyst compositions of the present invention may be prepared by one step synthesis of alcogels in which hydrolyzable matrix precursors are used in the presence of soluble metal salts and promoters. This preparative process is characterized by adding a solution of at least one catalytic metal compound selected from the group consisting of ruthenium and palladium to a solution of at least one metal alkoxide, wherein the metal is selected from the group consisting of Al, Ti, Nb, Zr, Ta, Si and other inorganic alkoxides, and gelling the resulting mixture. The order of addition of reagents, nature of precursors and solvents and the nature of gelling agents may be varied widely. The term gelling agent means a reagent that causes or facilitates the formation of a gel. It may be acidic, basic or neutral, such as of water.
General compositional ranges for the catalyst precursors herein are Ru and Pd from 0.1 to 20 wt %; the promoters Re and Sn from 0 to 20 wt % with the balance being the matrix material.
A typical preparation involves the incorporation of Ru, Pd, Sn, Mo or Re salts, or mixtures thereof, in an alkoxide solution of aluminum, silicon, titanium, zirconium, tantalum or niobium. The hydrolysis of the alkoxides can either be acid or base catalyzed. Hydrolysis of the alkoxide precursors is accompanied by condensation reactions. Under the proper conditions (pH, gelling agent, reactant ratios, temperature, time, solvent and solvent concentration), these can result in the polymerization into an inorganic gel containing the desired catalytic species or precursors. In some cases, the catalytic species are either part of the polymerization network, or are entrapped within the network.
A consequence of this method is that higher metal dispersion and uniformity can be achieved in the inorganic oxide matrix than is normally attainable using more conventional synthetic methods.
The first step in the synthesis of gels consists of preparing solutions of the gel precursors, which may be, but are not limited to, alkoxides and other reagents and separate solutions containing protic solvents such as water. The alkoxide solutions are mixed with the solutions containing the protic solvents, and the alkoxides will react and polymerize to form a gel. The protic solvent can include water, with trace acid or base as catalyst to initiate hydrolysis. As polymerization and crosslinking proceeds, viscosity increases and the material can eventually set to a rigid “gel”. The “gel” consists of a crosslinked network of the desired material which incorporates the original solvent within its open porous structure. The “gel” may then be dried, typically by either simple heating in a flow of dry air to produce an aerogel or the entrapped solvent may be removed by displacement with a supercritical fluid such as liquid CO
2
to produce an aerogel, as described below. Final calcination of these dried materials to elevated temperatures (>200° C.) results in products which typically have very porous structures and concomitantly high surface areas.
In the preparation of the catalysts of the present invention, the active metal precursors and promoters can be added to the protic or the alkoxide containing solutions. After gelation, the metal salt or complex is uniformly incorporated into the gel network. The gel may then be dried and heated to produce xerogel or aergoel materials, as described below.
Because of the synthetic technique and the physical appearance of the alcogels materials produced, it is clear that the precursor xerogels and aerogels contain active metals and promoters in a highly dispersed state. Further processing to produce the final catalytic materi

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