Zeolite-supported cobalt catalysts derived from natural diatomite with high catalytic activity for catalyzing NaBH₄ hydrolysis

Zeolite NaX was successfully synthesized by using diatomite as a silicon source. The obtained zeolite NaX exhibited higher surface area and porosity than that obtained from a commercially available silicon source. The zeolite NaX was used as a catalyst support by impregnating it with cobalt for catalyzing H₂ production from NaBH₄ hydrolysis. The effects of cobalt content, catalyst weight, NaBH₄ concentration and reaction temperature on the rate were investigated. The optimal condition was 20 wt% cobalt, 2 mg of catalyst weight with 300 mg of NaBH₄/100 cm³ DI water. The results from in situ X-ray absorption spectroscopy revealed that oxidation state of cobalt in the fresh catalyst was Co²⁺/Co³⁺ and it was unchanged during reaction. Cobalt species played an important role in catalyzing H₂ production by facilitating the adsorption of BH₄⁻ ion via electron transferred from BH₄⁻ to cobalt. Reusability of catalyst was tested for four cycles and its efficiency was still high.