Mechanistic origins of accelerated hydrogenation of mixed alkylaromatics by synchronised adsorption over Rh/SiO2

Catalytic reactions of mixed substrates sometimes behave differently from those of individual substrates. For example, the hydrogenation of propylbenzene over Rh/SiO2 proceeds 120% faster in the presence of toluene. Such an acceleration effect does not agree with the well-accepted Langmuir-Hinshelwood reaction model. In this paper, we examined its mechanism experimentally and computationally. The hydrogenation experiment of vaporised aromatics confirmed that the acceleration was specific to the liquid phase with the isopropanol solvent. Direct adsorption measurements revealed that toluene adsorption synchronises with propylbenzene adsorption. Density functional theory calculations confirmed the associates of toluene and propylbenzene on the catalyst surface in the polar environment. The formation of associates increased the adsorption energy of toluene and decreased that of propylbenzene. Lowered adsorption energy reduces the activation barrier for catalytic reaction and intensifies the reaction rate beyond the Langmuir-Hinshelwood model prediction.

Automated summary

Catalytic reactions of mixed substrates sometimes exhibit different behavior compared to individual substrates. This paper investigates the hydrogenation of propylbenzene in the presence of toluene, which accelerates the reaction rate by 120%. The well-accepted Langmuir-Hinshelwood reaction model cannot explain this acceleration effect. Experimental and computational studies reveal that the acceleration is specific to the liquid phase with the isopropanol solvent, and it is caused by the formation of associates between toluene and propylbenzene on the catalyst surface in the polar environment.