Inhibitory effect of CO on NH3-SCR of NO over Mn/TiO2 catalyst at low temperature: Inhibitory mechanism investigated by in situ DRIFTS

Abstract

The reaction of NO with NH3 over Mn/Ti catalyst in the presence of CO has been investigated at low temperature. CO can significantly decrease the NOx conversion between 100 and 300 °C and improve the N2 selectivity, especially above 200 °C. Besides, flue gas compositions reduce the CO oxidation due to the competitive adsorption among them. The XPS data suggested that surface chemical states of spent Mn/Ti catalyst in the presence and absence of CO did not vary obviously, pointing to that the surface chemical states of Mn/Ti catalyst don't account for the decrease in NOx conversion. The transient reactions and in situ DRIFTS experiments suggested that CO can compete with NO to adsorb on Mn/Ti catalyst and it can remarkably restrain NH3 to be adsorbed on weakly acid sites due to that these sites were occupied by carbonate species. This leads to the marked decrease in NOx conversion at low temperature and an increase in N2 selectivity because the amount of NH3 adsorbed on weakly acid sites decreases and it is mainly adsorbed on strong acid sites. In addition, the gaseous CO does not interfere with the reaction of gaseous NO with adsorbed NH3.