Ammonia borane (NH3BH3, AB) serves as a promising material for chemical storage of hydrogen owing to its high hydrogen density and superior stability, in which the development of highly efficient heterogeneous catalysts toward AB hydrolysis plays a crucial role. Herein, we report Pt atomic clusters supported on MoO3-x nanorods using a two-step process: MoO3-x nanorods were synthesized at various calcination temperatures, followed by a further deposition-precipitation approach to obtain Pt/MoO3-x catalysts (denoted as Pt/MoO3-x-T, T = 300, 400, 500, and 600 °C). The optimized Pt/MoO3-x-500 catalyst exhibits a prominent catalytic performance toward hydrolytic dehydrogenation of AB for H2 generation, with a turnover frequency value of 2268.6 min-1, which stands at the top level among the reported catalysts. Moreover, the catalyst shows a remarkable stability with 90% activity remaining after five cycles. A combination investigation including HR-TEM, ac-HAADF-STEM, XPS, in situ CO-IR, XANES, and Bader charge analysis verifies the formation of Pt2+-Ov-Mo5+ (Ov represents oxygen vacancy), whose concentration is dependent on the strength of the metal-support interaction. Studies on the structure-property correlation based on an isotopic kinetic experiment, in situ FT-IR, and DFT calculations further reveal that the Mo5+-Ov sites accelerate the dissociation of H2O molecules (rate-determining step), while the adjacent Pt2+ species facilitates the cleavage of the B-H bond in the AB molecule to produce H2. This work provides a fundamental and systematic understanding on the metal-support synergistic catalysis toward robust H2 production, which is constructive for hydrogen storage and energy catalysis.
Keywords: ammonia borane; hydrolytic dehydrogenation; interface site; kinetic study; reaction mechanism.