ROOM-TEMPERATURE HYDROGEN-TRANSFER FROM LIQUID METHANOL OR 2-PROPANOLTO DIPHENYLACETYLENE OVER GROUP VIII METAL TIO2 PHOTOCATALYSTS

A study of the hydrogenation of diphenylacetylene (tolane) over UV-irr adiated metal/TiO2 powders in alcoholic media has been performed at ro om temperature. The nature of the alcohol exerts a net influence on th e activity and selectivity toward cis- and trans-diphenylethylene (sti lbene) formation, presumably because of the influence of alcohol on th e adsorption of tolane on the catalyst surface. The effect of the natu re of deposited metal is closely related to the difference between the amount of hydrogen abstracted and that detected in the gas phase whic h reflects the photoreductive ability of metal toward hydrogenation of unsaturated compounds at the expense of the H-2-evolution reaction. A lthough the transfer hydrogenation of tolane proceeds at a lower rate compared with the conventional catalytic hydrogenation process because of a low availability of hydrogen photogenerated from an alcohol, goo d yields in the reduction of tolane and high selectivities toward olef in formation can be achieved by using in situ photogenerated hydrogen. The results obtained in this work show that the photoassisted transfe r hydrogenation reaction can constitute a practical synthesis method, particularly by using Pd/TiO2 which exhibits outstanding performance i n tolane reduction.