DFT study on the effect of oxygen vacancy and H2O in Mn-MOF-74 on SCR reaction
As one of the main air pollutants, nitrogen oxides (NOx) have serious effect on human health and the environment. Our previous work found that Mn-MOF-74 shows excellent catalytic performance for selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR) at low temperature. To obtain a further understanding of NH3-SCR mechanism in Mn-MOF-74, this paper would investigate two important parts in NH3-SCR process in Mn-MOF-74 using the density functional theory (DFT) method. On the one hand, the structural characteristics of two oxygen vacancies of Mn-MOF-74, namely carboxyl oxygen vacancy and hydroxyl oxygen vacancy, and their adsorption properties to reaction species were calculated. It was found that oxygen vacancies can not only activate the reaction species, but also promote the desorption of NO2 molecules from metal sites for the subsequent rapid SCR reactions. On the other hand, we studied the effect of H2O on the structural stability and catalytic performance of Mn-MOF-74. It was found that the interaction of Mn-O bonds in the framework of Mn-MOF-74 was weakened by H2O molecule. Therefore, the influence of H2O should be considered in the future design of MOFs catalysts for SCR process.