Catalytic hydrolysis of sodium borohydride for hydrogen production using phosphorylated silica particles

Hydrolysis of sodium borohydride (NaBH₄) offers substantial applications in the production of hydrogen but requires an inexpensive catalyst. Herein, silica (SP) and phosphorylated silica (SP-PA) are used as a catalyst for the generation of hydrogen from NaBH₄ hydrolysis. The catalyst is prepared by sol-gel route synthesis by taking tetraethyl orthosilicate as the precursor of silica whereas phosphoric acid served as the gelation and phosphorylating agent. The prepared catalyst is characterized by FT-IR spectroscopy, XRD, SEM, and EDAX. The hydrogen generation rate at SP-PA particles (762.4 mL min^-1 g^-1) is higher than that of silica particles (133 mL min^-1 g^-1 of catalyst). The higher catalytic activity of SP-PA particles might be due to the acidic functionalities that enhance the hydrogen production rate. The kinetic parameters (activation energy and pre-exponential factor) are calculated from the Arrhenius plot and the thermodynamic parameters (enthalpy, entropy, and free energy change) are evaluated using the Erying plot. The calculated activation energy for NaBH₄ hydrolysis at SP-PA catalyst is 29.92 kJ.mol^-1 suggesting the high catalytic activity of SP-PA particles. The obtained entropy of activation (ΔS‡ = - 97.75 JK^-1) suggested the Langmuir-Hinshelwood type associative mechanism for the hydrolysis of NaBH₄ at SP-PA particles.