Hydrogenation of carbonylic compounds Part I: Competitive hydrogenation of propanal and acetone over noble metal catalysts

The hydrogenation of propanal and of acetone have been studied as model for reactions of aldehydes and ketones. It has been confirmed that on all metals studied here, propanal reacts more slowly than acetone, just opposite to the homogeneous catalysts. Competitive hydrogenation experiments brought results which strongly suggest that this finding should be related to the different adsorption modes, possible with either homogeneous or heterogeneous catalysts. A solid surface offers contiguous adsorption sites which induce a higher population of more firmly adsorbed (and less reactive) species. Observations made on ether formation could be explained by means of an older model, according to which two different species react on a large ensemble of surface atoms. (C) 2000 Elsevier Science B.V. All rights reserved.