Hydrogenation of ketones over bifunctional Pt-heteropoly acid catalyst in the gas phase

Gas-phase hydrogenation of a wide range of ketones to alkanes, including hydrogenation of aliphatic ketones and acetophenone, was investigated using bifunctional metal-acid catalysis. The catalysts were comprised of a metal (Pt, Ru,Ni, and Cu) supported on acidic caesium salt of tungstophosphoric heteropoly acid Cs-2.5 H0.5PW12O40 (CsPW). The reaction occurred via a sequence of steps involving hydrogenation of ketone to alcohol on metal sites followed by dehydration of alcohol to alkene on acid sites and finally hydrogenation of alkene to alkane on metal sites. Catalyst activity decreased in the order: Pt > Ru >> Ni > Cu. Pt/CsPW showed the highest catalytic activity, giving almost 100% alkane yield at 100 degrees C and 1 bar pressure. Evidence is provided that the reaction with Pt/CsPW at 100 degrees C is limited by ketone-to-alcohol hydrogenation, whereas at lower temperatures (<= 60 degrees C) by alcohol dehydration yielding alcohol as the main product. The catalyst comprised of a physical mixture of Pt/C+CsPW was found to be highly efficient as well, which indicates that the reaction is not limited by migration of intermediates between metal and acid sites in the bifunctional catalyst. (C) 2014 Elsevier B.V. All rights reserved.