Solid-state mechanochemical synthesis of Rh/Al2O3 catalysts for effective hydrolysis of ammonia borane

Aluminium oxide (Al2O3) is a promising catalyst support due to its excellent stability, high specific surface area, low price, and wide applicability. At present, most of the synthesis methods of Al2O3 are wet chemical process, and the solid-state synthesis of catalysts is underdeveloped under solvent-free conditions. In this study, we proposed a novel strategy for solvent-free synthesis of Rh/Al2O3 catalysts via mechanochemistry. The pore properties of the catalysts can be tuned by simply adjusting the amount of template CTAB and calcination temperatures. As a proof of concept, as-prepared catalysts are used to catalyze hydrolytic dehydrogenation of ammonia borane. The best catalyst Rh/Al2O3-CTAB(0.4)-500 achieves a total turnover frequency of 186.0 mol(H2).mol(Rh)(-1).min(-1) at 298 K and the activation energy is 44.8 kJ.mol(-1). It also exhibits good cycling properties for catalyzing the hydrolysis of ammonia borane completely even after five runs. The catalysts were also characterized by various methods, including SEM, TEM, XPS, XRD, etc., to study the relationship between their structure and catalytic performance. The results show that the high activity of the catalyst is closely related to its large BET specific surface area and appropriate average pore size.