A New Application for Colloidal Silica Particles: Natural, Environmentally Friendly, Low-Cost, and Reusable Catalyst Material for H2 Production from NaBH4 Methanolysis

Metal nanoparticles (NPs) and metal composites (MCs) are generally used as catalysts for the methanolysis reaction of NaBH4. Here, we report the direct use of silica (SiO2) particles as an alternative catalyst for green energy carriers in H-2 generation from the methanolysis of NaBH4. The SiO2 particles of different sizes were synthesized using the very well-known Stober method and then treated with various acids such as hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), phosphoric acid (H3PO4), and acetic acid (CH3COOH). The hydrodynamic diameter of prepared SiO2 particles ranged between 200 and 800 nm measured by dynamic light scattering (DLS) with zeta potential values of about -46 and -37 mV. The BET surface area of SiO2 particles was measured between about 4-25 m2 g-1. The catalytic performances of the prepared SiO2 particles in methanolysis of NaBH4 were tested in terms of the effect and the type of treatment agents, acid and base, the hydrodynamic diameter of SiO2 particles, the reusability of the particle as catalyst, the regeneration effects of the particles, the concentration of NaBH4, and temperature. It was found that SiO2 particles are better if not comparable catalysts with metal NPs in terms of high reusability for H-2 production from the methanolysis reaction of NaBH4. The hydrogen generation rate (HGR) value from the methanolysis reaction of NaBH4 catalyzed by SiO2 particles treated with HCl was determined as 34 000 +/- 840 mL H-2 g(-1) min(-1) using 20 mL of 1000 mM NaBH4 and 50 mg of SiO2 as catalyst. The true activity of SiO2 particles treated with HCl was calculated as approximately 60% even after the 10th use. The activation energy (Ea) value for the NaBH4 hydrolysis reaction catalyzed by SiO2 particles was also found to be comparable with the literature at 29.9 +/- 0.4 kJ mol-1. According to the obtained results, the prepared SiO2 particles can be an alternative catalyst instead of metal nanoparticles.