Toluene hydrogenation and ring-opening on bimetallic Pd-Pt/HY catalysts

Abstract

Bimetallic Pd-Pt/HY catalysts prepared by the co-impregnation method with an atomic variation of Pd/Pd+Pt were studied to convert toluene and methylcyclohexane. The catalysts were characterized by the BET method, chemisorption of CO by the pulse method, programmed temperature reduction (H2-TPR), and programmed ammonia thermo-desorption (NH3TPD). Results of chemisorption of CO and H2-TPR for Pd-Pt/HY catalysts suggest the existence of a strong interaction between Pd and Pt. The NH3-TPD showed that incorporating metals influences the percentage of relative distribution of weak/strong acid sites presented in decreasing order of acidity: Pd0Pt100/HY>Pd100Pt0/HY>Pd33Pt67/HY. Atomic composition Pd/Pd+Pt equal to 0.33, and relative distribution of weak/strong acid sites equal to 2, favor hydrogenation of toluene to methylcyclohexane in metal sites and subsequent skeletal isomerization in the acidic sites through dimethylcyclopentane intermediate and ring-opening in the metal sites, leading to increased formation of n-heptane relative to iso-heptane. Bimetallic Pd-Pt/HY catalysts prepared by the co-impregnation method with an atomic variation of Pd/Pd+Pt were studied to convert toluene and methylcyclohexane. The catalysts were characterized by the BET method, chemisorption of CO by the pulse method, programmed temperature reduction (H2-TPR), and programmed ammonia thermo-desorption (NH3TPD). Results of chemisorption of CO and H2-TPR for Pd-Pt/HY catalysts suggest the existence of a strong interaction between Pd and Pt. The NH3-TPD showed that incorporating metals influences the percentage of relative distribution of weak/strong acid sites presented in decreasing order of acidity: Pd0Pt100/HY>Pd100Pt0/HY>Pd33Pt67/HY. Atomic composition Pd/Pd+Pt equal to 0.33, and relative distribution of weak/strong acid sites equal to 2, favor hydrogenation of toluene to methylcyclohexane in metal sites and subsequent skeletal isomerization in the acidic sites through dimethylcyclopentane intermediate and ring-opening in the metal sites, leading to increased formation of n-heptane relative to iso-heptane.