Palladium nanoparticles encapsulated in carboxylic acid functionalized periodic mesoporous organosilicas as efficient and reusable heterogeneous catalysts for hydrogen generation from ammonia borane

Benzene-bridged periodic mesoporous organosilicas (PMOs) are functionalized with carboxylic acid (−COOH) groups and used as the supports to immobilize Pd nanoparticles (Pd NPs). It is found that the −COOH functional groups play an important role in controlling the dispersion and growth of Pd NPs. Pd@PMOs are employed as the catalyst for hydrogen generation from hydrolysis of ammonia borane (AB) which shows turnover frequency (TOF) of 30.08 mol_H2 mol_Pd ^-1min^-1 and activation energy of 34.9 kJ mol⁻¹. The higher catalytic activity can be attributed to the small size and high dispersion of Pd NPs caused by the strong electrostatic interactions between the negatively charged carboxylate groups in the support and the positively charged Pd²⁺, favorable textural properties, and intrinsic hydrophobic property of the PMO s due to the presence of benzene groups inside the pore walls. The catalyst shows high durability since metal leaching is not a problem during recycling.