Comparative Study of HSOA-/SOA2-versus H3-BPO4B-Functionalities Anchored on TiO2-Supported Antimony Oxide-Vanadium Oxide-Cerium Oxide Composites for Low-Temperature NOX Activation
TiO2-supported antimony oxide-vanadium oxide-cerium oxide (SVC) imparts Lewis acidic (L)/Br？nsted acidic (B) sites, labile (Oα)/mobile oxygens (OM), and oxygen vacancies (OV) for selective catalytic NOX reduction (SCR). However, these species are harmonious occasionally, readily poisoned by H2O/sulfur/phosphorus/carbon, thus limiting SCR performance of SVC. Herein, a synthetic means is reported for immobilizing HSOA-/SOA2- (A= 3？4) or H3？BPO4B- (B= 1？3) on the L sites of SVC to form SVC-S and SVC-P. HSOA-/SOA2-/H3？BPO4B- acted as additional B sites with distinct characteristics, altered the properties of Oα/OM/OV species, thereby affecting the SCR activities and performance of SVC-S and SVC-P. SVC-P activated Langmuir-Hinshelwood-typed SCR better than SVC-S, as demonstrated by a greater Oα-directed pre-factor and smaller binding energy between Oα and NO. Meanwhile, SVC-S provided a larger B-directed pre-factor, thereby outperforming SVC-P in activating Eley-Rideal-typed SCR that dictated the overall SCR activities. Compared with SVC-S, SVC-P contained fewer OV species, yet, had higher OM mobility, thus enhancing the overall redox cycling feature, while providing greater Br？nsted acidity. Consequently, the resistance of SVC-P to H2O or soot were greater than or similar to that of SVC-S. Conversely, SVC-S revealed greater tolerance to hydro-thermal aging and SO2 than SVC-P. This study highlights the pros and cons of HSOA-/SOA2-/H3？BPO4B- functionalities in tailoring the properties of metal oxides in use as SCR catalysts.