Highly efficient MnCe/Ti catalyst for NH3-SCR of NO from sintering flue gas at low temperature: CO tolerance and reaction mechanism assessed by in situ DRIFTS

Abstract

The effect of metal doping (Ce, Fe, and Co) on CO tolerance of Mn/Ti catalyst used for eliminating NO from sintering flue gas has been investigated. The best MnCe/Ti catalyst achieves a NOx conversion of 80 % from 125 to 250 °C at a GHSV of 80,000 h−1. NOx conversion dropped by only 4 % below 200 °C and N2 selectivity slightly increased after introduction of CO, indicating strong resistance of MnCe/Ti catalyst to CO. XPS results suggest that CO oxidation does not alter surface content of Mn4+ and Ce3+ sites of used MnCe/Ti catalyst while it reduces the surface adsorbed oxygen of used MnCe/Ti catalyst because surface adsorbed oxygen consumed by CO oxidation cannot be readily replenished owing to the insufficient capacity in oxygen and electron transport. This is primarily accountable for the slight decrease in NOx conversion. Furthermore, NH3 can completely restrain CO adsorption on MnCe/Ti catalyst while CO cannot hinder the adsorption of NH3 and NO on the catalyst because the interaction between CO and MnCe/Ti catalyst significantly weakened in the presence of NH3, leading to the strong CO tolerance of MnCe/Ti. On MnCe/Ti Eley-Rideal mechanism governs the NH3-SCR involving gaseous NO and adsorbed NH3, while Mars-van Krevelen mechanism describes the oxidation of CO, indicating its reaction with gaseous CO and surface adsorbed oxygen. The findings in this paper can provide modification strategy for low-temperature SCR catalysts which are expected to be applied for sintering flue gas.