Dialectical Effects of MoO₃ Modification on the Pt/Al₂O₃ Catalyst for VOC Combustion due to the Molecular Structure...

An acid modification strategy has been intensively applied to improve the performance of noble metal catalysts in the catalytic combustion of volatile organic compounds (VOCs). However, the dependence of the acid modification effect on the molecular structure has not yet been focused on. In this work, using MoO₃-modified Pt/Al₂O₃ as model catalysts, and the catalytic combustion of VOCs with different molecular structure characteristics as probe reactions, it was revealed that MoO₃ modification showed a dialectical effect (promotional or inhibitory) on Pt/Al₂O₃ catalytic activity due to the molecular structure sensitivity. Further characterizations suggested that the enhanced surface acidity and more metallic Pt sites on MoO₃-modified Al₂O₃ would benefit the oxidation of alkanes (e.g., propane and cyclohexane) due to the alleviated alkane-O₂ competitive adsorption as well as the promoted C-H activation and intermediate decomposition/desorption, while the overstrong adsorption of VOCs containing π bond (e.g., toluene and propene) on MoO₃-modified Pt/Al₂O₃ significantly suppressed the deep oxidation process and thus resulted in an inferior reactivity. This work was the first to systematically investigate the molecular structure sensitivity of the acid modification effect on the catalytic performance of Pt catalysts, which would guide the rational design of efficient catalysts from the perspective of the molecular structure.