Mechanistic
Insight into the Synergetic Interaction
of Ammonia Borane and Water on ZIF-67-Derived Co@Porous Carbon for
Controlled Generation of Dihydrogen
posted on 2021-10-01, 08:15authored byMin-Hsuan Fang, Shiuan-Yau Wu, Yu-Hsiang Chang, Manmath Narwane, Bo-Hao Chen, Wei-Ling Liu, Darwin Kurniawan, Wei-Hung Chiang, Chia-Her Lin, Yu-Chun Chuang, I-Jui Hsu, Hsin-Tsung Chen, Tsai-Te Lu
Regarding
dihydrogen as a clean and renewable energy source, ammonia
borane (NH3BH3, AB) was considered as a chemical
H2-storage and H2-delivery material due to its
high storage capacity of dihydrogen (19.6 wt %) and stability at room
temperature. To advance the development of efficient and recyclable
catalysts for hydrolytic dehydrogenation of AB with parallel insight
into the reaction mechanism, herein, ZIF-67-derived fcc-Co@porous
carbon nano/microparticles (cZIF-67_nm/cZIF-67_μm) were explored
to promote catalytic dehydrogenation of AB and generation of H2(g). According to kinetic and computational studies, zero-order
dependence on the concentration of AB, first-order dependence on the
concentration of cZIF-67_nm (or cZIF-67_μm), and a kinetic isotope
effect value of 2.45 (or 2.64) for H2O/D2O identify
the Co-catalyzed cleavage of the H–OH bond, instead of the
H–BH2NH3 bond, as the rate-determining
step in the hydrolytic dehydrogenation of AB. Despite the absent evolution
of H2(g) in the reaction of cZIF-67 and AB in the organic
solvents (i.e., THF or CH3OH) or in the reaction of cZIF-67
and water, Co-mediated activation of AB and formation of a Co-H intermediate
were evidenced by theoretical calculation, infrared spectroscopy in
combination with an isotope-labeling experiment, and reactivity study
toward CO2-to-formate/H2O-to-H2 conversion.
Moreover, the computational study discovers a synergistic interaction
between AB and the water cluster (H2O)9 on fcc-Co,
which shifts the splitting of water into an exergonic process and
lowers the thermodynamic barrier for the generation and desorption
of H2(g) from the Co-H intermediates. With the kinetic
and mechanistic study of ZIF-67-derived Co@porous carbon for catalytic
hydrolysis of AB, the spatiotemporal control on the generation of
H2(g) for the treatment of inflammatory diseases will be
further investigated in the near future.