Crotonaldehyde hydrogenation over alumina- and silica-supported Pt-Sn catalysts of different composition. In situ DRIFT study

Alumina- and silica-supported bimetallic Pt-Sn catalysts with different Pt/Sn atomic ratios have been prepared by using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)(2)], the monometallic complex cis-[PtCl2(PPh3)(2)] and SnCl2 as metal precursors. Catalysts have been characterised by X-ray diffraction and transmission electron microscopy techniques, including energy-dispersive X-ray microanalysis, electron diffraction experiments and lattice-fringe microanalysis. The phase composition of the different catalysts has been related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). Results show that catalysts containing platinum-tin alloy phases with large particles are more selective towards the hydrogenation of the carbonyl bond to yield crotyl alcohol. The presence of oxidised tin species on the surface of the large alloy particles promotes the hydrogenation of the carbonyl bond. In situ diffuse reflectance infrared spectroscopy studies of crotonaldehyde adsorption under He or H-2 reveal differences between bimetallic catalysts and monometallic, and these differences have been related to the different catalytic behaviour of the catalysts.