Catalytic properties of metal-graphite intercalates for the hydrogenation of carbon monoxide

Typescript (photocopy).Alkali metal-graphite intercalates, NaC(,64), KC(,24) and KC(,8) and an iron-containing potassium-graphite (4.5 wt. % Fe) possess large adsorption capacities for carbon monoxide and exhibit high initial activities for CO hydrogenation at 300(DEGREES)C and 700 Torr total pressure. Carbon dioxide generation by a water-gas-shift reaction is prevented in all cases by the immediate and continuous removal of by-product water via interaction with intercalated alkali metal species. The latter process causes a complete and irreversible loss of catalytic activity after a cumulative conversion that for KC(,8), is equivalent to one CO molecule per three interlamellar potassium atom/ions, suggesting a lack of interlayer penetration by CO reactant. Adsorption and subsequent reaction of carbon monoxide over all of these materials apparently occurs on sites associated with intercalated alkali metal species located primarily along the exposed edges of graphite planes. The regular spacing of these sites appears to regulate the length of hydrocarbon produced as suggested by the change in product hydrocarbon chain length in progressing from KC(,8) to KC(,24) and NaC(,64). 2.2 wt. % iron-graphite and 3.4 wt. % cobalt-graphite each exhibit a shift to higher molecular weight products when compared to commercial iron/alumina and cobalt/kieselguhr catalysts at 225 to 325(DEGREES)C and 200 to 350(DEGREES)C, respectively, each using a 2/1 H(,2)/CO reactant ratio at 700 Torr total pressure. The shift is most apparent for the C(,2)-C(,3) hydrocarbons. Both transition metal graphite catalysts show a rather substantial and stable C(,2)('+) hydrocarbon selectivity with increasing reaction temperature. Associated with the hydrocarbon selectivity for iron-graphite is a significant reduction in CO(,2) produced versus that observed for the commercial iron/alumina catalyst. The cobalt-graphite catalyst exhibits an increase in activation energy and an apparent second order in hydrogen. Such behavior as is observed for cobalt/graphite, is indicative of metal support interactions. The product selectivity for iron- and cobalt-graphites and kinetic parameters for cobalt-graphite appear to be related to site heterogeneity associated with metal-support-interactions. The exact nature of the active sites and the kinetic expression which governs those sites is not known