Theoretical study on the effect of Mn promoter for CO2 reforming of CH4 on the Ni(1 1 1) surface

Abstract The reaction mechanism of CO2 reforming of CH4 on the Mn doped (Mn-Ni) and Mn adsorbed Ni(1 1 1) surface (Mn@Ni) have been investigated by using the density functional method. For Mn-Ni and pure Ni(1 1 1), the reaction mechanism is the same. i.e., CH4 + CO2 → CH + O + CO + 3H → CHO + CO + 3H → 2CO + 2H2. The rate determining step is CH + O → CHO with an energy barrier of 1.22 eV for Mn-Ni and 1.18 eV for pure Ni. For Mn@Ni, the mechanism is CH4 + CO2 → CH2 + O + CO + 2H → CH2O + CO + 2H → CHO + CO + 3H → 2CO + 2H2. The rate determining step is CO2 → CO + O with an energy barrier of 1.27 eV. Thus, for Mn@Ni, the carbon deposition is hindered effectively without much loss of the catalytic activity. This is also confirmed by microkinetic study in which the reaction rate for CH → C + H is low for Mn@Ni compared with Mn-Ni. In addition, the adsorbed Mn atom increases the utilization of CO2 and the reaction rate is more sensitive to the CO2/CH4 ratios than the reaction temperature.