Enhanced Catalytic CO Oxidation Activity and SO2 Resistance of Pt/Mo/TiO2 Catalysts by NH3 Pretreatment of Mo/TiO2

In this study, Pt/N-Mo/TiO2 and Pt/Mo/TiO2 catalysts were prepared by the two-step impregnation method for catalytic CO oxidation, with the obtained Mo/TiO2 pretreated or not with NH3 before Pt loading. The Pt/N-1Mo/TiO2 catalyst exhibited superior catalytic activity compared to Pt/1Mo/TiO2 and Pt/N-xMo/TiO2 (x = 0, 0.5, 2, 3, 5), indicating the essential role of N-modification of Mo/TiO2 with an optimal MoO3 loading. The T90 decreased from 133 °C for Pt/1Mo/TiO2 to 105 °C for Pt/N-1Mo/TiO2 under a feed gas consisting of 8000 ppm CO, 16% O2, 3% H2O and balanced N2. For both Pt/1Mo/TiO2 and Pt/N-1Mo/TiO2 catalysts, the H2O in the feed gas showed promotive effects on CO oxidation, while SO2 caused some deactivation at low temperatures. Under the same feed gas composition (8000 ppm CO, 16% O2, 10% H2O, 50 ppm SO2 and balanced N2) and temperature (185 °C), Pt/N-1Mo/TiO2 demonstrated superior SO2 resistance compared to Pt/1Mo/TiO2. CO conversion on Pt/N-1Mo/TiO2 remained above 99% during a 12-h SO2 resistance test, while that on Pt/1Mo/TiO2 gradually decreased to 26%. Characterization results show that NH3 pretreatment of 1Mo/TiO2 significantly improved the dispersion of Pt and enhanced the dissociation of adsorbed H2O into highly reactive hydroxyl (*OH) species, partially explaining the better activity of Pt/N-1Mo/TiO2 compared with Pt/1Mo/TiO2. H2O might promote CO oxidation by facilitating the formation of easily decomposable bicarbonate and formate intermediates. SO2 impeded the Pt reduction process on Pt/1Mo/TiO2 while it hardly affected that on Pt/N-1Mo/TiO2, explaining their difference in SO2 resistance.