Abstract

Palladium and platinum nanoparticles on an activated carbon were used as catalysts in the citral hydrogenation reaction in liquid phase at 363 K and 620 kPa of hydrogen pressure. The effect of metallic precursor salt to prepare mono and bimetallic catalysts was evaluated using PdCl2, Pd(NO3)2 and H2PtCl6. X-ray Photoelectron Spectroscopy suggests that Pdº, Pdδ+ (with δ close to 0) and Ptº are present on the monometallic catalysts surface; while Pdδ+, Pdn+, Ptδ-and Ptδ+ (with δ ≅ 0 and n ≅ 2) are detected on the bimetallic Pd-Pt/C. Monometallic PtCl/C displayed a very low total conversion of citral. All Pd based catalysts (PdN/C, PdCl/C and Pd-Pt/C) were highly selective to citronellal and isopulegol (desired products). The bimetallic Pd-Pt/C was the most active and selective catalyst. Electrondeficient and electron-rich species, chlorine amount on carbon surface and the modification of surface groups produced during the catalysts synthesis played an important role on the selectivity values to obtained products.

Keywords: Activated carbon, Citral, Hydrogenation, Nanoparticles, Palladium, Platinum.