Catalytically active Rh species stabilized by zirconium and hafnium on zeolites

Abstract

Supported subnanometric metal species and metal nanoparticles, prepared through the impregnation method, are widely used in industrial catalysis, but suffer from poor stability of the metal species to sintering at high reaction temperatures. Here, we report that hafnium (Hf) could stabilize rhodium (Rh) metal species supported on zeolites by forming Rh–[O]_x–Hf species to resist sintering in an oxidizing or reducing atmosphere at high temperatures (600–700 °C). The resulting RhHf/S-1 is highly efficient in generating H₂ from the hydrolysis of ammonia borane (AB), exhibiting a turnover frequency (TOF) of 363 mol_H2 mol_Rh⁻¹ min⁻¹ at 25 °C, which is more than 3-fold improvement over that of Hf-free Rh/S-1 (119 mol_H2 mol_Rh⁻¹ min⁻¹). The catalyst also shows superior catalytic activity in the cascade reactions of AB hydrolysis and the hydrogenation of various nitroarenes. Besides the Hf atoms, zirconium (Zr) atoms can also prevent the sintering of precious metal atoms. This sinter resistant strategy can also be extended to platinum (Pt) and ruthenium (Ru) atoms and other supports such as commercial SiO₂. This work provides a facile strategy for dispersing and stabilizing precious metal clusters with Zr and Hf additives by a simple impregnation method which will be important for many catalytic processes.