Support effects on Ru–HPA bifunctional catalysts: Surface characterization and catalytic performance Original Research Article

The behaviour of three metal–acid bifunctional catalysts, where the metal was Ru and the acid function was a heteropolyacid (HPA), was compared in the hydroconversion of n-hexane. Both the activity and the selectivity pattern depended on the used support: silica, high surface area graphite (HSAG) or zeolite KL. While Ru–HPA–SiO2 gave selectivity to isomerization products of 97%, the Ru–HPA–KL sample gave a selectivity of 96% to hydrogenolysis products. And, the performance of Ru–HPA–HSAG lied between that for Ru–HPA–SiO2 and Ru–HPA–KL, giving both isomerization and hydrogenolysis products, with selectivities of 45 and 54%, respectively. The series of techniques applied to characterize the catalysts have assisted in understanding the catalytic performance. The HPA phase has been detected over all the HPA-modified supports, but different acid sites strength distributions have been determined by calorimetry of NH3 adsorption, following the order HPA–SiO2 > HPA–HSAG > HPA–KL. Also, different Ru species have been observed on the catalysts surface due to the interaction between the Ru precursor and the HPA support. Finally, the analysis of the results has suggested that the support determines the role played by both metal and acid functions, which separately would lead to hydrogenolysis and isomerization reactions, respectively.