Clean Hydrogen Release from Ammonia Borane in a Metal–Organic Framework with Unsaturated Coordinated Tm3+

Abstract

A hybrid of ammonia borane (AB) and a metal–organic framework (MOF), which contains unsaturated coordinated Tm3+, Tm(BTC) (BTC = 1,3,5-benzenetricarboxylic), was synthesized through the solvent-based impregnation method (named as AB@Tm(BTC)–CH3OH). Also two other materials AB@Tm(BTC)-milled and AB@Tm2O3-milled were prepared by physical milling separately. TPD-MS results show that the H2-release peaks of the three materials shift to lower temperature, 77, 79, and 85 °C, respectively, compared with neat AB (114 and 150 °C). To avoid the undesirable volatile byproduct, only AB@Tm(BTC)–CH3OH shows superior performance without any byproduct, especially ammonia. The three samples exhibit enhanced dehydrogenation kinetics compared to neat AB, but AB@Tm2O3-milled presents much slower than the other two materials. The dehydrogenation activation energies of AB@Tm(BTC)–CH3OH, AB@Tm(BTC)-milled, and AB@Tm2O3-milled are 98.1, 103.1, and 116.4 kJ·mol–1, respectively. The mechanisms of the AB@MOF thermal dehydrogenation system especially for the prevention of ammonia have been discussed. The interaction between AB and the unsaturated coordinated metal sites in MOFs plays a key role for inhibiting ammonia during AB thermolysis.