Catalytic removal of NO<italic>_x</italic> and N₂O over combined V₂O₅/TiO₂ and Cs/Co₃O₄ catalysts

Aiming at efficiently removing NOx and N2O from the tail gas of nitric acid production， a technique route of catalytic reduction of NOx followed by catalytic decomposition of N2O was proposed. NOx reduction over V2O5/TiO2 catalyst and N2O decomposition over Co3O4-based catalysts were separately investigated. The combined removal of NOx and N2O was then investigated by connecting the V2O5/TiO2 catalyst with the optimized 2.0Cs/Co3O4 catalyst in series. Physicochemical characteristics of the catalysts were characterized by N2 adsorption-desorption， XRD， XPS， and O2-TPD techniques. The results showed that， for NOx reduction over the V2O5/TiO2 catalyst， the presence of 2% H2O in the feed gas could broaden the active temperature window of the catalyst， improve the N2 selectivity， and inhibit the formation of N2O. By loading 2.0% Cs on Co3O4， the N2O decomposition was greatly improved， which might be explained by the reduction of some Co3+ to Co2+ and the formation of more oxygen vacancies on the catalyst surface， due to the introduction of Cs. At high temperatures （400 ℃）. the presence of 2.0% H2O in the feed gas showed weak inhibitory effects on the decomposition of N2O over the 2.0Cs/Co3O4 catalyst， while the coexistence of 2% H2O and 50×10-6 NO significantly deactivated the 2.0Cs/Co3O4 catalyst. When the two-stage catalyst， consisting of upstream V2O5/TiO2 and downstream 2.0Cs/Co3O4 catalyst， was used to remove NOx and N2O， NOx was mainly reduced over the V2O5/TiO2 catalyst， with limited influence from the presence of N2O. In the temperature range for efficient removal of NOx （and NH3） over the V2O5/TiO2 catalyst， N2O could be stably decomposed over the downstream 2.0Cs/Co3O4 catalyst. With 2% H2O contained in the feed gas， complete conversion of NOx and NH3 was achieved at 400 ℃， whereas the conversion of N2O reached 61.3%.