A DFT study on adsorption behaviors of NH3 and SO2 on MnCe/TiNTs catalyst

Abstract

Manganese-cerium catalyst has attracted much attention due to its extraordinarily good low-temperature performance for detrinification technology, but its poor SO2 resistance limits its wide application. A suitable catalyst carrier can enhance the low-temperature activity and anti-poisoning performance of catalyst. In this paper, density functional theory (DFT) was used to construct MnCe catalyst models that supported by conventional TiO2 and TiO2 nanotubes (TiNTs) (denoted as MnCe/TiO2 and MnCe/TiNTs, respectively) to simulate adsorption behaviors of NH3 and SO2 molecules on catalyst surface. The adsorption energies (Eads) of NH3 and SO2 on catalyst surface, projected density of states (PDOS) of surface metal/nonmetal atoms and Mulliken charge were calculated. The results show that NH3 and SO2 molecules prefer to adsorb on top sites of Mn and Ce atoms respectively, but the competitive adsorption between NH3 and SO2 for top site of Ce atom on MnCe/TiO2 surface exists, for their Eads values (-0.42 eV and -0.44 eV) are similar. TiNTs alleviates their competitive adsorption by increasing the adsorption capacity of NH3 and weakening that of SO2 on catalyst surface. It attributes to the fact that TiNTs increases the coordination unsaturation of Mn and Ce atoms that enhances the electron transformation from NH3 molecule to Mn atom and weakens the electron-donating ability of Ce atom to SO2 molecule. In addition, TiNTs own abundant hydroxyl groups (OH) which can act as surface Brønsted acid sites for NH3 adsorption. These facts deeply reveal the promotion mechanism of TiNTs for low-temperature denitrification activity and sulfur poisoning resistance of MnOx-CeO2 catalyst from a microscopic perspective.