Selective ring opening of decalin on Rh-Pd/SiO2-Al2O3 bifunctional systems: Catalytic performance and deactivation

Ring opening of decalin was studied using Rh-Pd(x) catalysts supported on SiO2-Al2O3, prepared by coimpregnation with a variable total metallic content (x = 1, 1.5 and 2 wt%) while maintaining constant the Rh/Pd atomic ratio (equal to 1). The catalytic performances of these bimetallic systems were compared to those of monometallic Pd and Rh (1 wt%) catalysts. Bimetallic Rh-Pd(x) catalysts were unable to achieve decalin conversion and ring opening selectivity as high as those obtained using the Rh catalyst (~71 and ~67%, respectively, after 6 h reaction time). The principal cause was the reduction of the hydrogenolytic activity and acidity caused by the combination of Pd and Rh. In the case of the bimetallic Rh-Pd(x) samples, an increase in the metal content favored the formation of dehydrogenated products, reduced cracking (by reducing the concentration of strong acid sites) and increased coke deposition during decalin ring opening. Conversely, the Rh catalyst showed less deactivation since its efficient hydrogenolytic character eliminates coke precursors.