Synthesis,characterization of SiO2 supported-industrial phosphoric acid catalyst for hydrolysis of NaBH4 solution

Abstract

Tunisian industrial phosphoric acid H₃PO₄ was supported on silica gel SiO₂ (SIPA) to catalyze the hydrolysis reaction of aqueous alkaline sodium borohydride (NaBH₄). The SiO₂ was produced from purified quartz sand using alkali fusion-acidification chemical process. The BET surface area results indicate that the prepared silica gel could reach a specific surface area up to 585 m²/g. The addition of PO₃H₂ functional groups resulted in an increase of surface acidity of SiO₂ catalyst as shown by FT-IR and DTA-DTG spectra. The total acidity of SIPA catalyst was determined by titration to be 2.8?mmol H⁺/g. SEM/EDS maps reveal the distribution of heavy metals on the silica surface. The effect of supported PO₃H₂ functional groups and heavy metals on the NaBH₄ hydrolysis reaction was studied for different ratios of SIPA catalyst to NaBH₄. The sample 12SIPA/NaBH₄ leads to a very high hydrogen generation rate (up to 90%). The activation energy of hydrogen generation by NaBH₄ hydrolysis was 25.7?kJ mol^?1.