Mechanism of gas-phase sulfur modified Fe-Ce catalysts in the NH3-SCR reaction

Fe-Ce catalysts were prepared and then sulfated with SO2 in the selective catalytic reduction of NO by NH3. S-CPFe-Ce with precipitation method exhibited the highest activity, which is due to large specific surface area, the abundance of oxygen vacancies as well as the formation of Fe-O-Ce structure, thus contributing to the strong redox capacity. Furthermore, sulfates on S-CP-Fe-Ce facilitate the conversion of Lewis acid sites to Bro<spacing diaeresis>nsted acid sites, and promote the transformation of low-active nitrates to highly active nitrates, which is crucial for enhancing its activity. Besides, NH3 adsorbed over S-CP-Fe-Ce easily undergoes oxidation and dehydrogenation to form-NH2, which further reacts with gaseous NO, causing the superior catalytic performance. Additionally, NO was activated to form highly active monodentate nitrate and cis-N2O22-, enabling the rapid reaction with NH3, leading to the outstanding the catalytic activity. The NH3-SCR reaction of S-CP-Fe-Ce simultaneously involves ER and L-H mechanisms.