PtSn/SiO2 catalysts prepared by controlled surface reactions for citral hydrogenation in liquid phase Original Research Article

Bimetallic PtSn/SiO2 catalysts with broad Sn/Pt atomic ratios were prepared by an organometallic method using a controlled surface reactions (CSRs) between hydrogen adsorbed on silica-supported Pt and tin tetraethyl. The catalytic behavior of these catalysts was studied in citral hydrogenation in liquid phase carried out at 70 °C and atmospheric pressure. The catalysts were characterized by test reactions of the metallic phase (cyclohexane dehydrogenation (CHD), and cyclopentane hydrogenolysis (CPH)), CO chemisorption and Mössbauer spectroscopy. All these results clearly showed that tin was introduced exclusively into platinum. Results of citral hydrogenation show that the contribution of different reaction routes strongly depends on the metallic loading of both Pt and Sn, thus giving either a high selectivity to citronellal (CAL) or to unsaturated alcohols nerol + geraniol (UA), for monometallic and bimetallic catalysts, respectively. The citronellal cyclization resulting in the formation of isopulegol, was almost negligible because of the low concentration of acidic sites of the support. It was observed that the higher the Pt loading, the lower the Sn/Pt atomic ratio required to get higher UA selectivities. Products of undesirable side reactions were detected in trace amount. The results of CO chemisorption and CHD test reaction provided unambiguous prove that, due to the addition of tin, the catalytic properties of the metallic phase have been modified. Thus, results show that modified catalysts are highly selective for the hydrogenation of the carbonyl group.