Study on the role of Mn species in low temperature SCR on MnOx/TiO2 through experiment and DFT calculation

Abstract

The reaction mechanism of selective catalytic reduction of NO with ammonia (SCR) on MnOx/TiO2 catalysts was investigated through experiments and density functional theory (DFT) calculation. Firstly, the catalytic performance of catalyst with different molar ratios of MnOx/TiO2 was investigated and then was analyzed by NH3 temperature programmed desorption (NH3-TPD). The crystalline structure and the valence state of the MnOx/TiO2 catalyst were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). According to the results, the model of MnOx/TiO2 was established. Secondly, the different active sites of catalyst surface and adsorption characteristics of reacting gases during the SCR reaction based on in-situ DRIFT was investigated. Finally, the energy of different elemental reaction and isomerization of intermediate was calculated by MS Dmol3. It was found that the main active substance of catalyst was Mn4+ species which distributed dispersedly on the catalyst surface. The introduction of MnOx dopant can promote the adsorption of gas and reduce the formation energy of oxygen vacancy. The complete catalytic cycle goes in three steps: (a) Lewis acid site reaction follows Eley-Rideal mechanism; (b) Brønsted acid site reaction follows Langmuir-Hinshelwood mechanism; (c) Regeneration of catalyst.