Removal of toluene over bi-metallic Pt-Pd-SBA-15 catalysts: Kinetic and mechanistic study

A series of bi-metallic Pt-Pd-SBA-15 catalysts which promoted the dispersion of Pt-Pd by surface functionalization of SBA-15 were prepared and applied for toluene oxidation. We found that PVP-assisted Pt-Pd-SBA-15 exhibited the minimal average particle size (4.6 nm) and the highest Pt-0/Ptn+ (50.6%) among all the catalysts decorated with polyvinylpyrmlidon (PVP), citric acid and ethylenediamine, respectively. Kinetic study revealed that the Ea of all catalysts decreased accompanied with catalytic activity in the following order: Pt-Pd-SBA-15-PVP (83.5 kJ/mol) < Pt-Pd-SBA-15-citric (100.1 kJ/mol) < Pt-Pd/SBA-15 (110.7 kJ/mol) < Pt-Pd-SBA-15-(en)(2) (150.6 kJ/mol). Based on the above analyses, a conclusion could be drawn that PVP-induced dispersion process improved significantly the surface Pt-0/Ptn+ (50.6%) ratio and reduced the particle size of Pt-Pd nanoparticles, which enhanced the activity of toluene oxidation. Furthermore, in-situ DRIFTS studies showed that benzoic acid and maleic acid were typical intermediates produced during the catalytic combustion of toluene. Wherein, toluene could be oxidized to benzoic acid by positively charged Pt and Pd in the absence of O-2. On the other hand, toluene was oxidized to maleic acid under an aerobic atmosphere.