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 gamma-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/gamma-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/gamma-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 PtOx 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/gamma-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.