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

Abstract

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, ZrO₂ was selectively used to immobilize Ni nanoparticles, followed by a subsequent reduction at different temperatures to obtain Ni/ZrO_x-T catalysts (T denotes reduction temperature, T = 300–600 °C). The Ni/ZrO_x-500 catalyst displays a tremendous enhancement of the reaction rate to 114.41 mol_H2 mol_Ni⁻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 °C, which leads to the formation of an interfacial structure (Ni²⁺–O_v–Zr³⁺) induced by electron transfer from Ni to the ZrO_x support. Kinetic isotope effect studies combined with in situ FT-IR measurements confirm that Ni²⁺–O_v–Zr³⁺ serves as an active structure for AB hydrolysis, in which O_v–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 H₂ production.