Kinetics study on hydrolytic dehydrogenation of alkaline sodium borohydride catalyzed by Mo-modified Co–B nanoparticles

Abstract

Mo-modified Co–B nanoparticles have been prepared by the co-deposition chemical reduction method. The relationship between microstructure, catalytic activity and kinetics performance for H2 generation by hydrolysis of alkaline NaBH4 is studied. Compared to unmodified Co–B nanoparticles, the synthesized Co–Mo–B nanoparticles exhibit smaller particle size with average diameter of 30 nm, more uniform distribution with unconspicuous agglomeration, and larger specific surface area. The induced Mo in the Co–Mo–B catalyst exists as molybdenum oxides, which facilitates the dissociation of water due to weakening of the bond strength of the H–OH bond and promote the hydrolysis reaction of NaBH4. As a result, the maximum hydrogen generation rate and the activation energy of the hydrolysis reaction catalyzed by Mo-modified Co–B catalyst reach to 4200mLH2min−1gcatalyst−1 and 43.7 kJ mol−1, respectively, which are superior to those of the Co–B catalyst. Kinetic studies show that, in low concentration of NaBH4, first-order reaction is observed with respect to NaBH4 concentration, indicating that surface adsorption of BH4− is the rate-limiting step. At high NaBH4 concentration, hydrolysis reaction is zero-order, and the hydrolysis rate depends on surface reaction of adsorbed molecules.