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

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 H-2-release peaks of the three materials shift to lower temperature, 77, 79, and 85 degrees C, respectively, compared with neat AB (114 and 150 degrees 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.