Use of nickel catalysts and copper/nickel catalysts is well known for use in catalyzing gas-phase chemical reactions (non-aqueous phase chemical reactions) as seen in U.S. Pat. No. 4,251,394 to Carter et al. Carter et al. teach a co-precipitation of nickel together with the copper and silicate ions resulting in a catalyst containing an amount of nickel from about 25 wt % to about 50 wt % and an amount of copper from about 2 wt % to about 10 wt %. The nickel within the nickel/copper/silicate catalyst begins reduction in the presence of hyrdogen at about 200.degree. C. lower than a nickel/silicate catalyst. They further demonstrate that the improved reduction of the nickel is not observed when the copper is simply added to a nickel/silicate catalyst surface. Under non-aqueous conditions (benzene in cyclohexane), they demonstrated that the nickel/copper/silicate catalyst had greater activity than the nickel/silicate catalyst.
The use of a nickel/copper/chromia catalyst in the presence of water, ammonia and aqueous ammoniacal solutions is discussed in U.S. Pat. No. 3,152,998 to Moss. Moss describes the necessity of a high fraction of reduced nickel (at least about 30% of the nickel) in order for the catalyst to be resistant to attrition in an aqueous ammoniacal solution. The catalyst is made from soluble salts, for example nitrates, of nickel, copper and chromium that are co-precipitated resulting in a catalyst composition of 60-85% nickel, 14-37% copper and 1-5% chromium. The catalysts are used to produce heterocyclic nitrogen compounds including piperazine and carbon-substituted alkyl derivatives, cycloalophatic amines from cycloalkanols and morpnoline and carbon-substituted alkyl derivatives. For reactions at temperatures from 150.degree. C. to 400.degree. C., the catalyst particles are demonstrated to remain whole for about 18 to 23 days.
Another patent, U.S. Pat. No. 4,146,741 to Prichard, also discusses catalyzed reactions in an aqueous phase. Prichard converts furan to 1,4-butanediol and tetrahydrofuran in a dicarboxylic acid and water in the presence of a catalyst of nickel/copper/chromium on a support. The thrust of this patent is the use of dicarboxylic acids and a non pyrophoric nickel catalyst. The amount of nickel may range from 1 to 60 wt %. The added copper (2 to 35 wt %) is shown to improve the yield of diol product. No comment is made with respect to catalyst integrity with or without one of the metal constituents. Prichard does not specify a useful support but indicates that any of several conventional support materials can be used.
Sinfelt, Journal of Catalysis, shows nickel copper alloy catalyst and states
. . alloying of copper with nickel leads to catalytic effects in hydrogenolysis which are dramatically different from those observed for hydrogenation, dehydrogenation reactions . . .
Thus, it is clear from Sinfelt that alloying of copper with nickel leads to increased catalytic activity compared to use of nickel alone. Surface areas of catalysts range from 0.63 m.sup.2 /g for 5% copper in nickel alloy 1.46 m.sup.2 /g for 95% copper in nickel alloy. Although Sinfelt reports low surface area catalysts in his paper, U.S. Pat. No. 3,617,518 describes a copper nickel alloy dispersed on supported catalyst providing a higher surface area.
More recent work by Elliott et al. (Ind. Eng. Chem. Res. Vol. 32, No. 8, pp. 1542-8, 1993) has focused upon aqueous phase reactions at 350.degree. C., wherein it was discovered that the commercially available catalysts (nickel-only) interacted with the water in the aqueous phase resulting in agglomeration or sintering of the catalytic metal (nickel-only) dispersed upon the support thereby reducing the activity and effective life time of the catalysts. The commercially available catalysts tested was a range of commercially produced supported nickel metal catalysts used for hydrogenation, steam reforming, and methanation reactions. In addition, Elliott et al. found that commercially available silica, alumina, and silica-alumina catalyst supports were not stable in an aqueous processing environment. Because Prichard operated a batch process making no time based observations of his catalyst, and because his process was limited to about 7 or 8 hours, he would not have observed any degradation of catalyst and therefore would have no motivation to solve the problem of limited catalyst life in aqueous media at elevated temperatures required for a continuous process. The problem of support stability is avoided by Moss by the use of an alloy catalyst with a small amount of chromia binder.
It has been reported by R Srinivasan, R J DeAngelis, B H Davis Catalysis Letters, 4 (1990) 303-8 that improved activity of Sn/Pt catalysts for hydrocarbon reforming in a gas phase reaction might be explained by Sn stabilization of Pt crystallites formed on alumina. However, ratios of 3 to 4 of Sn to Pt were required for maximum effect, but alloy formation is not believed to be the cause.
Further, K Balakrishnan and J Schwank, Jour. of Catalysis, 132 (1991) 451-464 report that Sn addition reduces the activity for Pt catalyzed hydrocarbon reforming in the gas phase at 300.degree. C. while improving the activity maintenance. In contrast, Au (gold) addition improved the activity but made no significant difference in the rate of deactivation.
However, until Elliott et al., the problem of nickel agglomeration for aqueous phase reactions at these temperatures was not observed. Accordingly, there is a need for a catalyst that avoids agglomeration in aqueous phase reactions.
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