Experimental and DFT studies on diesel-steam-reforming to hydrogen over a bimetallic Rh–Ni-based MgO-Al₂O₃ microsphere catalyst

Surface modification of 600-µm-sized monodisperse gamma-alumina microspheres into magnesium–aluminum spinel, and co-impregnation-based loading of Rh–Ni (0.46 wt% Rh, 9.03 wt% Ni) were performed to synthesize catalysts for diesel-steam-reforming to hydrogen. The intimate interactions between Rh and Ni, the formation of the Rh–Ni alloy, and the Rh-doping-induced decrease in the particle size of Ni were determined. The DFT calculations results revealed that Rh-doped Ni(1 1 1) established remarkably weak bonds with oxygen-containing intermediates, and the reaction barrier of the rate-limiting step (CH₂* + O* → CH₂O*) on Rh–Ni(1 1 1) (0.76 eV) was lower than those of Ni(1 1 1) (1.14 eV) and Rh(1 1 1) (1.56 eV). The bimetallic catalyst shows the enhanced activity and resistance of sintering and carbon deposition compared with those of Ni-based (9.33 wt% Ni) and Rh-based (0.47 wt% Rh) catalysts. The catalytic performance of Rh–Ni-based catalyst was superior to that of physically mixed Ni-based and Rh-based catalysts at similar active metal loadings, which further confirmed the synergistic effect of Rh–Ni.