BIFUNCTIONAL CONDENSATION-REACTIONS OF ALCOHOLS ON BASIC OXIDES MODIFIED BY COPPER AND POTASSIUM

Alcohol dehydrogenation and condensation reactions are involved in cha in growth pathways on Cu/MgCeOx promoted with potassium. These pathway s lead to the formation of isobutanol with high selectivity via reacti ons of higher alcohols with methanol-derived C-1 species in reaction s teps also relevant to higher alcohol synthesis from CO/H-2 mixtures at higher pressures on K-Cu/MgCeOx catalysts. Ethanol reactions on K-Cuy Mg5CeOx show that both Cu and basic sites participate in alcohol dehyd rogenation and aldol condensation steps leading to n-butyraldehyde and acetone. Chain growth occurs by condensation reactions involving a me tal-base bifunctional aldol-type coupling of alcohols. Reactions of (C 2H5OH)-C-12-(C2H4O)-C-13 mixtures show that direct condensation reacti ons of ethanol can occur without requiring the intermediate formation of gas phase acetaldehyde. Reactions of C2H5OH/D-2 mixtures show that Cu sites increase the rate of aldol condensation by introducing recomb inative desorption sites that remove hydrogen atoms formed in C-H acti vation steps leading to the unsaturated aldol-type species required fo r chain growth. Reactions of acetaldehyde and C-13-labeled methanol le ad predominantly to 1-C-13-propionaldehyde and 2-C-13-isobutyraldehyde , both of which lead to isobutanol during CO/H-2 reactions. Mixtures o f propionaldehyde and C-13-labeled methanol lead to singly-labeled iso butyraldehyde. Chain growth to C2+ alcohols occurs via addition of a m ethanol-derived C-1 species to adsorbed oxygen-containing intermediate s. The gradual appearance of C-13 in the unlabeled reactant within the se mixtures shows that aldol coupling reactions are reversible. Revers e aldol condensation reactions after intramolecular hydride transfer l ead to the formation of acetone from ethanol. Isobutyraldehyde is a pr eferred end-product of aldol-type chain growth reactions of alcohols b ecause it lacks the two ct-hydrogens required for subsequent chain gro wth. (C) 1998 Academic Press.