Synergistic catalysis over Ni/ZrOx for hydrogen production from hydrolysis of ammonia borane

Ammonia borane (AB) is broadly researched as a hydrogen storage medium because of its safe storage and high hydrogen density. However, the development of efficient catalytic systems on non-precious metal catalysts is still a big challenge. Herein, ZrO<INF>2</INF> was selectively used to immobilize Ni nanoparticles, followed by a subsequent reduction at different temperatures to obtain Ni/ZrO<INF>x</INF>-T catalysts (T denotes reduction temperature, T = 300-600 degrees C). The Ni/ZrO<INF>x</INF>-500 catalyst displays a tremendous enhancement of the reaction rate to 114.41 mol<INF>H<INF>2</INF></INF> mol<INF>Ni</INF>-1 min-1 and the turnover frequency (TOF) to 196.82 min-1. HR-TEM and XPS characterization techniques verify that the strength of metal-support interaction (MSI) enhances firstly and then decreases as the reduction temperature elevates from 300 to 600 degrees C, which leads to the formation of an interfacial structure (Ni2+-O<INF>v</INF>-Zr3+) induced by electron transfer from Ni to the ZrO<INF>x</INF> support. Kinetic isotope effect studies combined with in situ FT-IR measurements confirm that Ni2+-O<INF>v</INF>-Zr3+ serves as an active structure for AB hydrolysis, in which O<INF>v</INF>-Zr3+ directly participates in the rate-determining step (water dissociation) while Ni2+ accelerates the B-H bond cleavage. This work provides a useful paradigm for the rational design and preparation of cost-effective catalysts for AB hydrolysis with a high H<INF>2</INF> production.