Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the preparation method Original Research Article

The effect of the preparation method on the catalytic behavior of bimetallic PtSnC catalysts in the vapor phase hydrogenation of crotonaldehyde has been determined. Nine PtSnC bimetallic catalysts have been prepared by coimpregnation and by successive impregnations of the support with solutions of the metal precursors, with SnPt atomic ratios ranging from 0 to 1.43. The effect of these variables on the surface characteristics of the catalysts has been analyzed by hydrogen and carbon monoxide chemisorption at room temperature and by X-ray photoelectron spectroscopy (XPS), and they have been related to the catalytic behavior in the title reaction. Results show that both metallic and oxidized tin species are present in the reduced catalysts (hydrogen, 623 K, 12 h) and their relative amounts depend on the preparation method and on the SnPt ratio. The overall activity for the title reaction increases with tin content, with a maximum for SnPt of about 0.8, and then decreases for higher tin loadings. The selectivity for the hydrogenation of the carbonyl bond in competition with the reduction of the olefinic CC bond seems to be related to the relative amount of oxidized surface tin species. The best results in terms of activity and selectivity are achieved with catalysts in which the tin precursor has been loaded first.