Ni Nanoparticles Supported on CeO₂ as Catalysts for Aqueous-Phase Glycerol Reforming

Abstract

The efficient production of hydrogen by aqueousphase reforming (APR) of biomass-derived polyols demands the nanoscale bifunctionality of the catalyst, including dehydrogenation and decarbonylative C−C bond cleavage. Though nickelbased catalysts have been widely studied in the APR reaction, the approach to regulate the bifunctionality in this catalytic system still remains elusive. In this work, Ni/CeO 2 nanocatalysts of different Ni contents were synthesized and employed for APR of glycerol. The rates for dehydrogenation and decarbonylative C−C bond cleavage reached the optimal balance for catalysts containing 20−30 wt % Ni, leading to the highest hydrogen productivity. Complementary characterizations revealed that Ni of lower contents mainly formed the small Ni particles of the oxidized state as the active site for dehydrogenation; however, it lacked the functionality for C− C cleavage, limiting the overall rate of hydrogen production. In contrast, the high content of Ni formed large particles that created two domains of Ni, i.e., metallic and oxidized Ni, which acted as the sites for decarbonylative C−C bond cleavage and dehydrogenation, respectively. Further increasing the content of metallic Ni triggered more methanation reactions that consumed the produced hydrogen. Only when the bifunctionality in nanoscale is well coordinated and the desirable reaction steps are balanced can the production of H 2 be maximized. This work may provide a mechanistic understanding about the bifunctionality of Ni-based nanocatalysts in the APR reaction.