Unraveling SO-tolerant mechanism over Fe(SO)/TiO catalysts for NO reduction.

Developing low-temperature SO-tolerant catalysts for the selective catalytic reduction of NO is still a challenging task. The sulfation of active metal oxides and deposition of ammonium bisulfate deactivate catalysts, due to the difficult decomposition of the as-formed sulfate species at low temperatures (<300 °C). In recent years, metal sulfate catalysts have attracted increasing attention owing to their good catalytic activity and strong SO tolerance at higher temperatures (>300°C); however, the SO-tolerant mechanism of metal sulfate catalysts is still ambiguous. In this study, Fe(SO)/TiO and Ce(SO)/TiO catalysts were prepared using the corresponding metal sulfate salt as the precursor. These catalysts were tested for their low-temperature activity and SO tolerance activity. Compared to Ce(SO)/TiO, Fe(SO)/TiO showed significantly better low-temperature activity and SO tolerance. It was demonstrated that less surface sulfate species formed on Fe(SO)/TiO and Ce(SO)/TiO. However, the presence of NO and O could assist the decomposition of NHHSO over Fe(SO)/TiO at a lower temperature, endowing Fe(SO)/TiO with better low-temperature SO tolerance than Ce(SO)/TiO. This study unraveled the SO-tolerant mechanism of Fe(SO)/TiO at lower temperatures (<300 °C), and a potential strategy is proposed for improving the low-temperature SO-tolerance of catalysts with Fe(SO) as the main active component or functional promoter.