NiAl₂O₄ Spinel Supported Pt Catalyst: High Performance and Origin in Aqueous-Phase Reforming of Methanol

The production of hydrogen from the aqueous-phase reforming (APR) of oxygenated hydrocarbons is promising. Herein, the performances of Pt loaded on NiAl₂O₄ spinel and γ-Al₂O₃ were investigated in the APR of methanol. The conversion of methanol and the yield of hydrogen over Pt/NiAl₂O₄ reached 99.9% and 95.7%, respectively. In comparison with Pt/γ-Al₂O₃ catalyst (26.5% and 23.3%, respectively), these values were enhanced by 4-fold. More importantly, Pt/NiAl₂O₄ had high stability with only 10% loss of its initial conversion after 600 h on stream. In situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) of the APR of methanol revealed that the reaction underwent the dehydrogenation of methanol and the sequential water–gas shift (WGS) reaction. These two reactions were then investigated independently, in which Pt/NiAl₂O₄ showed more efficient performance than Pt/γ-Al₂O₃. Intensive characterization methods revealed that the chemical state of Pt played a pivotal role in the dehydrogenation of methanol to generate the adsorbed CO intermediate. For Pt/NiAl₂O₄ catalyst, the reduction of PtO_x to metallic state Pt was easier because of the presence of the oxygen vacancy, leading to the higher catalytic performance in the dehydrogenation of methanol. Further studies with in situ DRIFTS-MS of WGS demonstrated a redox mechanism over Pt/NiAl₂O₄ catalyst, which was different from the associative route that occurred over Pt/γ-Al₂O₃ and made the WGS reaction faster. The addition of Ni (NiAl₂O₄ spinel) creates oxygen vacancies, giving WGS which underwent a redox route. This work presents the deep understanding into the pathway and mechanism in the APR of methanol and is expected to have important implications for the future development of APR catalysts.