Reaction mechanism for NH3-SCR of NOx over CuMn2O4 catalyst

Abstract

The relationship between the types of active sites and the selective catalytic reduction (SCR) activity of NO with NH3 over CuMn2O4 spinel was established through density functional theory (DFT) calculations. A skeletal reaction scheme including the possible elementary steps was proposed to understand N2, NO2 and N2O formation during NH3-SCR of NO over CuMn2O4 catalyst. DFT calculation results show that chemisorption mechanism is responsible for the adsorption of reactants, possible intermediates and products over CuMn2O4(100) surface. 2-fold coordinated surface Cu atom plays a crucial role in NH3-SCR of NO, because it is the active site for NH3 and NO adsorption. NH2 produced from NH3 dehydrogenation is identified as a key reactive intermediate of SCR reaction. NH2 easily reacts with the adsorbed NO to form N2 and H2O via NH2* + NO* → N2* + H2O* which is activated by 6.87 kJ/mol. The activation energy barrier of N2O formation over CuMn2O4 catalyst is much higher than that of N2 formation, which indicates that CuMn2O4 catalyst shows a good N2 selectivity for NO reduction. The optimal reaction pathway for NH3-SCR of NO over CuMn2O4(100) surface is a two-step process controlled by NH3* + * → NH2* + H* and NH2* + NO* → N2* + H2O*. The rate-determining step of N2 formation during NO reduction is the first dehydrogenation reaction of NH3.