Comparative density functional theory study of carbon formation and removal mechanism on Rh modified Ni-based catalyst in the CH4/CO2 reforming

Rh catalyst shows promising performance for coke resistance in the CH4/CO2 reforming reaction. In this study, a single atom Rh was added to the surface of Ni(111) by doping and adsorbing ways, and the performance of these surfaces was compared with the pure Ni(111) through density functional theory (DFT) calculation. The reactions related to the carbon formation were studied to obtain the favored adsorption site and dominant reaction paths on three surfaces. A good linear relationship between the charge difference and the reaction barrier was proposed. On the Ni(111) surface, the highest energy barrier of CH* oxidation and decomposition is 1.24 and 1.30 eV, respectively, thus these two reaction paths are dominant. The most favorable pathway for the Rh/Ni(111) is CH* + O* -> CHO* -> CO* + H*, with the highest energy barrier of 1.34 eV. However, C* is more likely to be converted into C-C (C2) than oxidized on all three catalyst surfaces. As a result, Rh/Ni(111) surface shows better catalytic activity thermodynamically and more superior carbon deposition resistance. In general, compared with pure Ni catalyst, the modification of Rh could manipulate the reaction path of CH* consumption, which could inhibit the direct decomposition of CH*, and finally suppress the carbon deposition.