Ga and In promoters in bimetallic Pt based catalysts to improve the performance in the selective hydrogenation of citral

Abstract

In this paper, bimetallic PtGa and PtIn catalysts supported on multiwall carbon nanotubes and carbon Vulcan were used to study the hydrogenation of citral (alpha,beta-unsaturated aldehyde) in liquid phase to produce nerol and geraniol (unsaturated alcohols, UA). The catalysts were prepared with different metallic loadings by conventional impregnation. All the catalysts contained a Pt loading of 5wt%. Once reduced under hydrogen flow, the supported catalysts were characterized by test reactions of the metallic phase, H2 chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Hydrogenation results showed that the addition of a second metal to Pt leads to important modifications of the selectivity to UA. The highest selectivities to UA were reached with different promotor/Pt atomic ratios for Ga and In. The catalyst performances in the citral hydrogenation were related to the characteristics of each supported bimetallic phase. It was found that the PtGa catalysts have a typical behavior of an ionic promoter together with a contribution of the Ga reduced species, reaching high selectivities to UA. On the other hand, PtIn catalysts with a metallic phase composed mainly by zerovalent In species in contact with the metallic phase,also showed high activities and selectivities to UA. The best selectivity value to UA (about 97%) was found for PtIn(2.5wt%)/CN-P catalyst with an excellent activity.