ABSTRACT
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.
