Hydrogenation of crotonaldehyde on Rh-Sn/SiO2 catalysts prepared by reaction of tetrabutyltin on prereduced Rh/SiO2 precursors

Rh and Rh-Sn/SiO2 catalysts have been prepared, characterized and used in the crotonaldehyde hydrogenation reaction. New bimetallic Rh-Sn catalysts were prepared by reaction of Sn(n-C4H9)(4) over a prereduced Rh-SiO2 precursor. It was observed that the temperature of the preparation reaction also plays an important role in the nature of the Rh-Sn active sites. Thus, at lower temperatures. 363 K, Rh(SnBu4-x)(x) species remain adsorbed on the silica surface whereas at 773 K, the organometallic residue decomposes leading to Rh-Sn bimetallic catalysts. Tin addition causes a significant drop in hydrogen chemisorption capability but only a slight increase in metal particle size. Electron diffraction detected the presence of Rho. RhSn2 and SnO2 phases for the bimetallic catalysts and Rho for the monometallic ones. XPS shows an important surface enrichment in tin suggesting that SnOx species would migrate and deposit on the metal crystals. The active sites generated upon these treatments allow the polarisation of the carbonyl group and consequently an enhancement in the selectivity to crotyl alcohol is obtained. (C) 2002 Elsevier Science B.V. All rights reserved.