A Novel Catalyst and the Catalytic Mechanism for Aqueous-Phase Reforming of Methanol Coupling with Nitrobenzene Hydrogenation to Aniline

The coupling of aqueous-phase reforming of methanol (APRM) with nitrobenzene hydrogenation offers a potentially safe and atom-economical route to aniline. This work developed an efficient Pd–Cu/γ-Al2O3 catalyst, with 98.9% nitrobenzene conversion and 92.9% aniline selectivity. Characterization results reveal that this higher activity is attributed to the Pd–Cu alloy formation, which enriches the Cu+ and Pd0 species and the number of strong base sites. The Cu+/Pd0 synergy enhanced methanol adsorption and decomposition, while the strong base sites facilitated water activation, thereby accelerating the APRM to supply more in situ hydrogen for nitrobenzene hydrogenation. DFT results further confirmed that the Pd–Cu alloy formation can lower the energy barriers in key steps. Based on the identification of the byproducts, the reaction mechanism for this coupled system was proposed. Pd–Cu/γ-Al2O3 catalyst can be easily regenerated by calcination and reduction, without significant loss of catalytic activity after 3 consecutive cycles. It also exhibited broad substrate applicability for various nitroarenes.