SiO2-Encompassed Co@N-Doped Porous Carbon Assemblies as Recyclable Catalysts for Efficient Hydrolysis of Ammonia Borane.

Abstract

The development of earth-abundant catalysts for efficient hydrolysis of ammonia borane is of great importance in the conversion and utilization of hydrogen energy. Here, we report the synthesis of SiO2-encompassed Co@N-doped porous carbon assemblies as a new type of recyclable catalyst for the purpose by calcination of zeolitic imidazolate framework-67@SiO2 microtubes at high temperatures under an N2 atmosphere. We find that the surface layer of SiO2 in the precursor microtubes is essential for the production of efficient catalysts by supplying an additional surface for Co nanoparticle dispersion in an effort to reduce their size. In addition, the SiO2 layer renders a highly ordered arrangement of Co@N-doped porous carbon within the catalysts, possibly allowing the ease of mass transfer of ammonia borane within the catalysts. The optimized catalysts obtained via calcination at 800 °C show a set of remarkable catalytic benefits, including a high hydrogen generation rate of 8.4 mol min-1 mol(Co)-1, a relatively low activation energy of 36.1 kJ mol-1, and a remarkable reusability (at least 10 times). Our results can provide new insight into the design and synthesis of highly ordered SiO2-supported catalysts for different reactions.