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 (MCM41,FSM16 and SBA15) of different pore size and texture were synthesized by templating method. CoB nanoparticle catalysts were supported over these mesoporous silica by impregnation–reduction method in order to study the effect of support pore structure on the catalytic properties in H2 production by hydrolysis of Ammonia Borane (AB). TEM and N2 adsorption–desorption isotherm results clearly revealed that size, dispersion degree, and location of CoB 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 SBA15 whereas there is no correlation of the particle size and pore size for MCM41 and FSM16. CoB supported over SBA15 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 MCM41 and FSM16 supported catalyst. Higher activity for SBA15 support is mainly attributed to the geometrical confinement of CoB particles within the pores which creates smaller CoB particles (6 nm) with uniform size distribution and higher degree of dispersion as compared to MCM41 and FSM16 support where the CoB particles lie on the external surface with broad size distribution. Open and interconnected pores of SBA15 can also provide easy passage for reactant and product during the course of reaction. The CoB particles supported in the interconnected pores of SBA15 produce lower effective activation energy barrier related to the hydrolysis process of AB than that established with MCM41 and FSM16 supported catalyst. Most importantly, the thicker pore walls of SBA15 assist in avoiding the agglomeration of CoB particles and even provide high stability at elevated temperatures (873 K) at which unsupported CoB catalyst gets completely destroyed.