Effect of stabilizer type on the activity and stability of water-dispersible cobalt(0) nanocluster catalysts in hydrogen generation from the hydrolysis of sodium borohydride

摘要

Hydrogen phosphate (HPO4~(2-)) or poly(acrylic acid) (PAA) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the catalytic hydrolysis of sodium borohydride (NaBH4) in the presence of stabilizers, HPO4~(2-) or PAA. Cobalt(0) nanoclusters stabilized by HPO4~(2-) or PAA were characterized by using UV-Visible spectroscopy, TEM, XPS and FT-IR techniques. They were employed as catalysts in the hydrolysis of NaBH4 to examine the effect of stabilizer type on their catalytic activity and stability. Detailed reaction kinetics of the hydrolysis of NaBH4 in the presence of both catalysts was studied depending on catalyst concentration, substrate concentration and temperature. PAA stabilized cobalt(0) nanoclusters provided higher total turnover number (TTON = 6,600) than that of HPO4~(2-) stabilized cobalt(0) nanoclusters (1,285 turnovers). However, the HPO4~(2-) stabilized cobalt(0) nanoclusters provided a lower activation energy (E_a = 53 ± 2 kJ mo1~(-1)) than the PAA stabilized cobalt(0) nanoclusters (E_a = 58 ± 2 kJ mo1~(-1)) for the hydrolysis of NaBH4. The use of two types of stabilizers in the preparation of the same metal(0) nanoclusters following the same methodology enables us to compare the electrostatic and steric stabilization in terms of the catalytic activity and stability of metal(0) nanoclusters.