Hydrogenation of Unsaturated Organic Molecules Containing C═C and C═O Groups Catalyzed by the Ni(111) Surface─A Case Study of Maleic Anhydride

To elucidate the mechanism and product selectivity of maleic anhydride (MA) hydrogenation, we systematically investigated the reaction network on Ni(111) using DFT-D3 calculations. The minimum energy path was elucidated by evaluating the overall kinetics of the complete reaction network through the energy span model based on the TOF-determining transition state and intermediate (TDTS/TDI). Our results reveal a distinct kinetic divergence: C═C hydrogenation is highly facile, directly yielding succinic anhydride (SA), whereas the deep hydrogenation toward 1,4-butanediol (BDO) is hindered by high barriers. This rationalizes the experimentally observed high SA selectivity and negligible BDO formation. For C═O hydrogenation, the C-first/O-second hydrogenation sequence is kinetically favored, driven by strong oxygen–surface interactions that stabilize critical transition states and intermediates, which was determined by bader charge and partial density of states (PDOS) analysis. Furthermore, we identify a novel hydrogenation–deoxygenation mechanism where deoxygenation precedes further hydrogenation, with C–O scission acting as the rate-determining step. Ultimately, these atomic-level insights not only elucidate the intrinsic MA hydrogenation mechanism on Ni(111) but also provide a coherent theoretical framework to rationalize experimental product distributions and offer guidance for tailoring Ni-based catalysts toward the selective hydrogenation of unsaturated compounds containing C═C and C═O groups.