Transition metal-catalyzed dehydrogenation of hydrazine borane N2H4BH3via the hydrolysis of BH3 and the decomposition of N2H4

Hydrazine borane N2H4BH3 (denoted HB) is a novel candidate in hydrogen generation by catalytic hydrolysis. The challenge with this material is the dehydrogenation of the N2H4 moiety, which occurs after the hydrolysis of the BH3 group. This challenge requires the utilization of a reactive and selective metal-based catalyst. In this work, we considered various transition metal salts as precursors of in situ forming catalysts by reduction in the presence of HB. According to their reactivity, the metals studied can be classified into 3 groups: (1) Fe- and Re-based catalysts, showing a limited reactivity in the hydrolysis of the BH3 group; (2) Co-, Ni-, Cu-, Pd-, Pt- and Au-based catalysts, only active in the hydrolysis of BH3 (3 mol H2 per mol HB generated); (3) Ru-, Rh, and Ir-based catalysts, being also active in the decomposition of N2H4. With the Rh-based catalyst, characterized as agglomerated Rh0 nanorods (10 × 4 nm) by XRD, TEM, SAED and XPS, 4.1 mol H2 + N2 per mol HB can be produced at 50 °C. Rhodium is thus a possible candidate for synthesizing nanosized particles and bimetallic nanoalloys in order to tune its reactivity and increase its selectivity up to the targeted conversion of 100%. Our main results are reported herein and the behavior of the metals is discussed.

► The decomposition of the N2H4 group of hydrazine borane N2H4BH3 can occur at 50 °C.
► In situ formed Rh0, Ru0 and Ir0 are active in this decomposition.
► In situ formed Pt0, Pd0, Cu0, Au0, Ni and Co black are active in BH3 hydrolysis.
► In situ formed NH4ReO4 and Fe2O3 are not suitable in decomposition of N2H4BH3.
► Rh0 would present the most appropriate electronic environment for this reaction.