ISOBUTANOL AND METHANOL SYNTHESIS ON COPPER-CATALYSTS SUPPORTED ON MODIFIED MAGNESIUM-OXIDE

Alcohols are selectively produced from CO/H-2 on K-CuMgCeOx catalysts, but synthesis rates are strongly inhibited by CO2 formed during react ion. Reaction pathways involve methanol synthesis on Cu, chain growth to C2+ alcohols, and metal-base bifunctional coupling of alcohols to f orm isobutanol. Ethanol reactions on K-Cu0.5Mg5CeOx show that Cu catal yzes both alcohol dehydrogenation and aldol condensation reactions. Ce O2 increases Cu dispersion and MgO surface area and K decreases Cu dis persion, but increases the density of basic sites. Reactions of acetal dehyde and C-13-labeled methanol lead to 1-C-13-propionaldehyde, a pre cursor to isobutanol. The density and strength of basic sites were mea sured using a (CO2)-C-12/(CO2)-C-13 isotopic jump method that probes t he number and chemical properties of basic sites available at typical isobutanol synthesis temperatures. K or CeO2 addition to CuMgOx increa ses the density and strength of basic sites and the rates of base-cata lyzed ethanol condensation reactions leading to acetone and n-butyrald ehyde. The presence of CO in the He carrier during temperature-program med surface reactions of ethanol preadsorbed on Cu0.5Mg5CeOx decreases the rate of base-catalyzed condensation reactions of preadsorbed etha nol, possibly due to the poisoning of basic and Cu sites by the CO2 fo rmed from CO via water-gas shift reactions. (C) 1997 Academic Press.