Silica embedded cobalt(0) nanoclusters: Efficient, stable and cost effective catalyst for hydrogen generation from the hydrolysis of ammonia borane

Abstract

Cobalt(0) nanoclusters embedded in silica (Co@SiO 2) were prepared by a facile two-step procedure. In the first step, the hydrogenphosphate anion (HPO 4 2−) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the hydrolysis of sodium borohydride (NaBH 4) in the presence of stabilizer. Next, HPO 4 2− anion-stabilized cobalt(0) nanoclusters were embedded in silica formed by in situ hydrolysis and condensation of tetraethylorthosilicate added as ethanol solution. Co@SiO 2 can be separated from the solution by vacuum filtration and characterized by UV–Vis electronic absorption spectroscopy, TEM, SEM-EDX, ATR-IR and ICP-OES techniques. Co@SiO 2 are found to be highly active and stable catalysts in the hydrolysis of ammonia borane (AB) even at low cobalt concentration and room temperature. They provide an initial turnover frequency of 13.3 min −1 and 24,400 total turnovers over 52 h in the hydrolysis of AB at 25.0 ± 0.5 °C. Moreover, Co@SiO 2 retain 72% and 74% of the initial activity after ten runs recyclability and five cycles reusability test in the hydrolysis of AB, respectively. The kinetics of hydrogen generation from the hydrolysis of AB catalyzed by Co@SiO 2 was studied depending on the catalyst concentration, substrate concentration, and temperature. The activation parameters of this catalytic reaction were also determined from the evaluation of the kinetic data.