Improved thermal dehydrogenation of ammonia borane by MOF-5

Abstract

A composite material containing ammonia borane (AB) and MOF-5 has been synthesized by the infusion method. The decomposition temperature of this composite was much less than that of pristine AB. Temperature-programmed desorption mass spectrometry onset and peak temperatures of AB dehydrogenation were 60 °C and 84 °C, respectively. The hydrogen release rate of AB inside MOF-5 was markedly increased at a safe temperature of 85 °C. The activation energy of AB/MOF-5 was shown to be 68.45 kJ mol⁻¹. The formation of the main undesirable volatile byproducts borazine and diborane was prevented. However, ammonia was still released during dehydrogenation because of the lack of a coordinately unsaturated metal in MOF-5. We suggest that the coordinately unsaturated metal sites play the key role in preventing the escape of ammonia.