Hollow mesoporous aluminosilicate spheres imbedded with Pd nanoparticles for high performance toluene combustion

Abstract

In the past few decades, persistent efforts have been directed toward the stabilization of Pd nanoparticles during catalytic reaction processes carried out at relatively higher temperatures. In this study, small-sized Pd nanoparticles imbedded into hollow mesoporous aluminosilicate sphere catalysts (Pd/HMAS-1) have been synthesized. The physical and chemical properties of Pd/HMAS-1 were studied by the means of XRD, TEM, and XPS analysis. The prepared Pd/HMAS-1 catalyst was evaluated for its catalytic performance in the combustion of toluene. Pd/HMAS-1 showed excellent activity for toluene oxidation with T90 at 150 °C, which was much higher than that of Pd/HMAS-2 (T90 at 220 °C) with Pd nanoparticle supported on the external surface of HMAS and Pd/HMAS-CTAB (T90 at 200 °C) with perpendicular pore channel occupied by CTAB. Furthermore, Pd/HMAS-1 exhibited an outstanding long-term stability and maintained the conversion efficiency of 100 % at 200 °C for 20 h. The superior catalytic performance of Pd/HMAS-1 has been attributed to the confinement effect of ordered mesopore in stabilizing Pd nanoparticles and improvement in mass transfer efficiency and active Pd metal accessibility. Furthermore, the oxidation pathway of toluene over Pd/HMAS-1 was proposed based on the analysis of key intermediates generated during the catalytic combustion process by in situ-DRIFTS analysis. This study provides a promising strategy to design novel high-performance ordered mesoporous zeolite-confined metal/metal oxide catalysts for industrial VOCs combustion.