Mechanistic Study of Selective Catalytic Reduction of NOx with NH3 over Mn-TiO2: A Combination of Experimental and DFT Study

5 years ago

Mechanistic Study of Selective Catalytic Reduction of NOx with NH3 over Mn-TiO2: A Combination of Experimental and DFT Study

Jian Liu, Yongheng Li, Huiling Zheng, Sicong Ma, Weiyu Song, Zhen Zhao, Jianlin Deng, Yan Zhou

Mn-TiO₂ oxide catalyst has been studied intensively for selective catalytic reduction (SCR) of NO with NH₃ due to its extraordinarily good low-temperature performance. However, the mechanism of SCR on Mn-TiO₂ still remains unclear, especially with regard to the decomposition pathway of the NH₂NO intermediate and the reason for the decreasing N₂ selectivity with the increasing of temperature. In this work, we attempt to provide a molecular level understanding of these questions via a combination of DFT and experimental study. A complete catalytic cycle of the SCR reaction was proposed based on a model in which Mn is doped into the TiO₂(101) surface by quantum-chemical DFT+U calculations. In situ DRIFTS experiments were performed to provide evidence to the important intermediates as proposed in the reaction mechanism. The doping Mn enhances NH₃ adsorption and activation due to its lower conduction band. NH₂NO can decompose into N₂ and H₂O fast via a concerted H migration step. The decreasing selectivity with rising temperature can be explained by the deep oxidation of NH₃. This study provides atomic-scale insights into the catalytic cycle and the important role of doping Mn in NH₃–SCR reaction on Mn-TiO₂ catalysts, which is of significance for the design of high activity low-temperature SCR catalysts.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06715

DOI: 10.1021/acs.jpcc.7b06715