Performance of toluene oxidation over MnCe/HZSM-5 catalyst with the addition of NO and NH3

Abstract Toluene and NOx can be co-removed in NH3-SCR unit. The evaluation of toluene oxidation performance with the participation of SCR reactants is momentous but lacking. Herein, a MnCe/HZSM-5 catalyst was prepared to investigate the effects of NO and NH3 on toluene oxidation. The addition of NO and NH3 increased the toluene conversion from 76.6% to 91.8%, but decreased the CO2 selectivity from 60.5% to 34.1% at 250 °C, indicating that more carbon was transferred into the byproducts. NO and NH3 participated in toluene oxidation by reacting with intermediates, such as aldehydes, carboxylic acids or phenol, to form nitriles or nitrobenzene. Most of nitriles and nitrobenzene were in solid byproducts, which deposited on catalyst surface and deactivated the catalyst. SCR reactants accelerated the decrease of Mn4+, Ce3+, Osur proportions and Lewis acid sites, which were the active constituents for toluene oxidation. As a consequence, a faster deactivation occurred. NO was competitively adsorbed on catalyst with toluene, but promoted toluene oxidation. On the contrary, NH3 enhanced toluene adsorption, but inhibited toluene oxidation. The in-situ DRIFTs results showed that NO and NH3 inhibited the deep oxidation of toluene based on the observation of less water, carboxylate and carbonate.