Impact of NO and NH addition on toluene oxidation over MnO-CeO catalyst.

An increasing number of industries remove toluene from flue gas by the existing NH-selective catalytic reduction (NH-SCR) units. A thorough probe into the impact of NO and NH addition on toluene oxidation is imperative but still lacks a unified understanding. In this work, NH-SCR reactants are found to inhibit the toluene oxidation process over the MnO-CeO catalyst below 200 °C. The competitive adsorption between NH-SCR reactants and toluene, the NO adsorption state, and carbon deposition are emphasized to play important roles in this deactivation. Within the NO adsorption states, only the adsorbed NO can enhance the toluene oxidation. The formed nitrate species (NO) on the surface is inactive. NO adsorption is the weakest among the reactants with the smallest adsorption energy of -0.42 eV, restricting its promotion on toluene oxidation. NO and NO are both demonstrated to be inefficient to oxidize toluene. Meanwhile, MnO-CeO catalyst suffers from serious acetonitrile and benzonitrile poisoning. The amount of nitrile species accounts for ~95% of total carbon deposition, while no simple substance carbon (C) can be generated from CO disproportionation. Special care should be considered towards the formation of environmentally hazardous benzamide in the off-gas from the simultaneous NO and toluene removal process.