Comparative study of HSO/SO versus HPO functionalities anchored on TiO-supported antimony oxide-vanadium oxide-cerium oxide composites for low-temperature NO activation.

TiO-supported antimony oxide-vanadium oxide-cerium oxide (SVC) imparts Lewis acidic (L)/Brönsted acidic (B) sites, labile (O)/mobile oxygens (O), and oxygen vacancies (O) for selective catalytic NO reduction (SCR). However, these species are harmonious occasionally, readily poisoned by HO/sulfur/phosphorus/carbon, thus limiting SCR performance of SVC. Herein, a synthetic means is reported for immobilizing HSO/SO (A= 3-4) or HPO (B= 1-3) on the L sites of SVC to form SVC-S and SVC-P. HSO/SO/HPO acted as additional B sites with distinct characteristics, altered the properties of O/O/O 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 O-directed pre-factor and smaller binding energy between O 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 O species, yet, had higher O mobility, thus enhancing the overall redox cycling feature, while providing greater Brönsted acidity. Consequently, the resistance of SVC-P to HO or soot were greater than or similar to that of SVC-S. Conversely, SVC-S revealed greater tolerance to hydro-thermal aging and SO than SVC-P. This study highlights the pros and cons of HSO/SO/HPO functionalities in tailoring the properties of metal oxides in use as SCR catalysts.