Promotional effects of Ag on catalytic combustion of cyclohexane over PdAg/Ti-SBA-15

Abstract

Recently, PdM bimetallic nanoparticle-supported catalysts have attracted considerable attention as superior catalysts for VOC combustion due to the promotional effect rendered by the added second metal. However, the promotional effect is rarely investigated. In this study, Ti-SBA-15-supported bimetallic PdAg nanoparticle catalysts with different molar ratios were prepared. Compared to Pd/Ti-SBA-15 and Ag/Ti-SBA-15, Pd13Ag1/Ti-SBA-15 with a loading amount of 0.63 wt% exhibited superior activity. Furthermore, Pd13Ag1/Ti-SBA-15 exhibited outstanding stability in the on-stream reaction. The excellent catalytic performance of Pd13Ag1/Ti-SBA-15 was mainly ascribed to the synergistic effect of Pd and Ag in promoting the key steps of cyclohexane combustion. The reaction pathways of cyclohexane over the samples were proposed on the basis of the analysis of the key intermediates generated during catalytic combustion by in situ DRIFTS and PTR-TOF-MS. Higher concentrations of cyclohexene, benzene, and light olefins were generated over Pd13Ag1/Ti-SBA-15 in comparison with those generated over Pd/Ti-SBA-15 at a temperature range of 180–220 °C, demonstrating that the addition of Ag to Pd/Ti-SBA-15 promotes the key steps of the oxidative dehydrogenation of cyclohexane to benzene and catalytic cracking of cyclohexane to olefins due to the increase of Lewis and Bronsted acid sites over Pd13Ag1/Ti-SBA-15. Revealing the promotional effect of bimetallic catalysts on catalytic VOC combustion would be beneficial for the design of bimetallic catalysts with high efficiencies and cost-effectiveness.