Deactivation mechanism of arsenic and resistance effect of SO42− on commercial catalysts for selective catalytic reduction of NOx with NH3.

Arsenic (As) is found to be poisonous to the commercial V2O5WO3/TiO2 catalysts for selective catalytic reduction of NOx with NH3. The NOx conversion of catalysts declines and N2O formation dominates at high temperature (above 300 °C) after As poisoning. A series of activity and characterization experiments are applied to reveal the deactivation mechanism caused by As. Results indicate that doping of As on the catalysts, which exists as H2AsO4− and HAsO42−, doesn’t seriously change surface area of catalysts or TiO2 phase, but greatly decreases both the Lewis and Brønsted acid sites. It is found that VOH is destroyed and less reactive AsOH is newly formed. VOH site is crucial to the NH3 adsorption and its destruction by As contributes to catalyst deactivation. Besides, stronger oxidizability of catalysts that resulted from more surface-active oxygen aroused by As leads to substantial non-selective catalytic reduction reaction and NH3 oxidation at high temperature. Both of these two aspects result in lower NOx conversion and higher N2O formation. However, SO42− can provide remarkable surface acidities and the sites that destroyed by As can thus be supplied. Benefited from these new reactive acid sites, catalysts with prominent SO42− loading show superior arsenic resistance even with a high As content, which indicate to be a promising anti-poisoning formula. Finally, mechanism of arsenic poisoning and resistance effect of SO42− is proposed based on the above analysis.