Co-B catalyst supported over mesoporous silica for hydrogen production by catalytic hydrolysis of Ammonia Borane: A study on influence of pore structure

Three kinds of mesoporous silica (MCM-41, FSM-16 and SBA-15) of different pore size and texture were synthesized by templating method. Co-B nanoparticle catalysts were supported over these mesaporous silica by impregnation-reduction method in order to study the effect of support pore structure on the catalytic properties in H-2 production by hydrolysis of Ammonia Borane (AB). TEM and N-2 adsorption-desorption isotherm results clearly revealed that size, dispersion degree, and location of Co-B particle is affected by the pore texturing of the support. It also showed that the catalyst particle acquires directly the size of the support pores only for SBA-15 whereas there is no correlation of the particle size and pore size for MCM-41 and FSM-16. Co-B supported over SBA-15 silica was found to be the most active catalyst as inferred from the observed hydrogen generation rates in the hydrolysis reaction compared to that produced by MCM-41 and FSM-16 supported catalyst. Higher activity for SBA-15 support is mainly attributed to the geometrical confinement of Co-B particles within the pores which creates smaller Co-B particles (6 nm) with uniform size distribution and higher degree of dispersion as compared to MCM-41 and FSM-16 support where the Co-B particles lie on the external surface with broad size distribution. Open and interconnected pores of SBA-15 can also provide easy passage for reactant and product during the course of reaction. The Co-B particles supported in the interconnected pores of SBA-15 produce lower effective activation energy barrier related to the hydrolysis process of AB than that established with MCM-41 and FSM-16 supported catalyst. Most importantly, the thicker pore walls of SBA-15 assist in avoiding the agglomeration of Co-B particles and even provide high stability at elevated temperatures (873 K) at which unsupported Co-B catalyst gets completely destroyed. (C) 2013 Elsevier B.V. All rights reserved.