Gas-phase conversion of 1,3-butanediol on single acid-base and Cu-promoted oxides

Abstract

The gas-phase conversion of 1,3-diols was studied on catalysts containing different active sites and using 1,3-butanediol as a model molecule. Transformation of the diol primary and/or secondary OH groups by dehydration and dehydrogenation reactions yields valuable oxygenates combining OH and CC, OH and CO or CC and CO functions, along with other compounds. A series of single oxides with different acid-base properties, copper-silica and copper-single oxide catalysts were prepared by several methods and characterized by TPR, XRD and N2O chemisorption. Acid-base oxides transform 1,3-butanediol at low rates. Oxide electronegativity determines the main reaction pathway: acidic oxides promote 1,3-butanediol dehydration toward unsaturated alcohols and olefins, whereas basic oxides dehydrogenate-dehydrate the diol toward the unsaturated ketone. The effect of Cu0 in monofunctional copper-silica, or bifunctional copper-acid or copper-base catalysts, is to increase the reaction rate and to shift the reaction pathway toward 1,3-butanediol dehydrogenation. The metal dispersion depends on the preparation method by impregnation, ion exchange or co-precipitation. Small Cu0 particles strongly adsorb reactant and products allowing consecutive reactions to take place after initial dehydrogenation. In bifunctional catalysts, the role of the acid or base sites is to promote consecutive dehydration-hydrogenation or CC bond cleavage reactions, respectively.