Mitigation of polyborate precipitation on Pd/Fe2O3 sites during ammonia borane hydrolysis: An alternate insight into the role of oxygen vacancies

Understanding the stability of catalysts is essential for both fundamental science and industrial process design. Herein, we show that oxygen vacancies at the interfaces of Pd/Fe2O3 catalysts prevent the precipitation of polyborate byproducts on the catalyst's surface during ammonia borane (AB) hydrolysis, thereby enhancing the catalyst's stability. Fe2O3-supported Pd nanoparticles were synthesized by a solid-state approach wherein Fe2O3 support size was varied as 20 nm, 45 nm, and 70 nm while the Pd content was maintained at 5% by wt. With increasing cycles, the catalyst containing 20 nm Fe2O3 nanoparticle support is stable, while the catalysts with 45 and 70 nm Fe2O3 supports showed deterioration of catalytic activity. In lower support sizes, due to the fine dispersion of Pd, in-situ oxygen vacancies are created at Pd/Fe2O3 interface during AB hydrolysis. We propose that more water molecules congregate at the vacancy sites, which aids the solubility of polyborates, thereby extending the activity of the catalyst through multiple cycles.