Graphite-supported platinum-palladium bimetallic catalyst for aromatic hydrogenation of 4-propylphenol in aqueous ethanol solution under free-external hydrogen source

Abstract

Hydrogenation of 4-propylphenol (4PP) was studied over graphite-supported platinum-palladium (Pt-Pd/G) bimetallic catalysts in aqueous ethanol solution without the use of external source. Compared to the corresponding monometallic (Pt/G and Pd/G) catalysts, the prepared Pt-Pd/G bimetallic catalysts were more active for hydrogen production and aromatic hydrogenation to 4-propyl cyclohexanone (NONE), cis- and trans-4-propyl cyclohexanols (NOLs). Pt/G was active for hydrogen production but inactive for 4PP hydrogenation, and Pd/G catalyst was active for both hydrogen production and 4PP hydrogenation. Pt-Pd/G catalysts with different platinum to palladium ratios (Pt:Pd = 1:0, 1:1, 1:2, 1:4, 1:8 and 0:1) were prepared to obtain the best composition for the ring hydrogenation. Among the bimetallic catalysts prepared, the yields of NONE and NOLs were the highest over 0.5Pt-0.5 Pd/G (0.5 wt% platinum and 0.5 wt% palladium loadings, and Pt:Pd=1:2). TEM analysis showed small (3.1–3.3 nm) metal particles dispersed on the graphite surface in the bimetallic catalysts. EXAFS analysis showed the formation of platinum core-palladium enriched shell structure of bimetallic particles. It was suggested that the high activity of Pt-Pd/G catalysts for 4PP hydrogenation in aqueous ethanol solution was caused by the formation of small platinum-palladium alloy particles on graphite surface and that palladium on the surface of particles was the active site. This work demonstrated Pt-Pd/G as highly active catalysts for aromatic hydrogenation of 4PP without the use of any external hydrogen source.