Understanding the adsorption of NH3, NO and O2 on the MnOx/SiO2 β-cristobalite (101) surface with density functional theory

Abstract

Based on the density functional theory, the adsorption processes of NH3, and NO and O2 on the Mn active sites of MnOx/SiO2 β-cristobalite (101) surface were simulated. The results show that NH3, NO and O2 can be effectively adsorbed on the Mn active sites of both MnO2/SiO2 β-cristobalite (101) and Mn2O3/SiO2 β-cristobalite (101) surface. The adsorption characteristics of the two catalysts are different. The adsorption energy of NH3 molecule on the MnO2/SiO2 β-cristobalite (101) surface is much higher than that on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The NO molecule and the O2 molecule are a little easier to be adsorbed on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The large difference of NH3 adsorption energy between the two catalysts becomes one of the main reasons why MnO2/SiO2 has better catalytic activity than Mn2O3/SiO2. Furthermore, the high adsorption energy of NH3 on MnO2/SiO2 surface proves that SiO2 is an excellent carrier and MnO2/SiO2 catalyst is an outstanding NH3-SCR catalyst at low temperature.