Platinum catalysts on alumina and silica prepared by gas- and liquid- phase deposition in cinnamaldehyde hydrogenation

Abstract

Platinum catalysts supported on alumina and silica were prepared by gas-phase deposition and impregnation using (trimethyl)methylcyclopentadienylplatinum(IV) as precursor. The deposition from the gas-phase was carried out at 100 °C with nitrogen as carrier gas, and in impregnation, the deposition was carried out with toluene as solvent at room temperature in inert atmosphere. In both cases, a ligand exchange reaction of the platinum precursor occurred with the support surface with simultaneous reduction of platinum(IV) to platinum(II) and platinum(0). Post-treatment of the catalyst materials was studied by direct reduction under hydrogen (only impregnated catalysts) and by calcination in air prior to reduction. The catalysts were characterised by CO-chemisorption, temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity and selectivity were assessed by hydrogenation of cinnamaldehyde. The results showed that the support, the method of preparation and post-treatment influence the dispersion and catalytic properties. A calcination step before the reduction increased the dispersion values on both alumina and silica. The catalysts on alumina support had high dispersion, >90%, whereas the catalysts supported on silica had a dispersion of 36% when produced in the gas-phase and 24% when produced by impregnation. The catalysts on silica support were more active in cinnamaldehyde hydrogenation than those on alumina support. The impregnated platinum catalyst supported on silica showed selectivity to cinnamyl alcohol up to 90% at conversion of 15%. The advantage of preparing platinum catalyst with (trimethyl)methylcyclopentadienylplatinum(IV) as precursor was that no acid-catalysed products were then formed in the hydrogenation reaction.