Pt, PtSn and PtGe catalysts supported on granular carbon for fine chemistry hydrogenation reactions

Abstract

Two series of PtSn and PtGe catalysts with different metallic loadings, supported on activated carbon powder, were prepared by successive impregnation. Both the effects of the second metal addition and the Sn or Ge loading on the activity and selectivity in the carvone and the citral hydrogenations (used as catalytic tests) were investigated. In all cases the support was purified to eliminate undesirable elements such as sulfur and, for high Pt loadings, carbon was functionalized with nitric acid so as to introduce more oxygen-containing groups. The carvone hydrogenation was carried out with PtSn catalysts, the Pt and Sn loadings being very low. The citral hydrogenation was carried out with PtSn and PtGe catalysts with higher metal loadings supported on both purified, and purified and functionalized carbons. Besides, the effect of the branched solvent in the activity and selectivity of the citral hydrogenation reaction was also studied with PtSn catalysts. The catalysts were characterized by temperature-programmed reaction (TPR), test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), hydrogen chemisorption and by X-ray photoelectron spectroscopy (XPS). The catalytic activity in the carvone hydrogenation showed a maximum for the monometallic catalyst with respect to the Sn loading. For the catalyst with the highest tin loading (0.4 wt%) even though the activity drastically decreased, the selectivity to the doubled unsaturated alcohol (carveol) was very important. Although the citral hydrogenation gave very good results with PtSn systems with high metallic loadings, the opposite happened with the PtGe ones. Moreover, the more branched solvents modified the selectivity to unsaturated alcohols of the PtSn catalyst in the citral hydrogenation.