The effect of temperature, catalyst and sterics on the rate of N-heterocycledehydrogenation for hydrogenstorage

Abstract

Efficient hydrogen storage is one of the critical requirements for the use of hydrogen fuel cells in light-duty vehicles. Our investigation of reversible chemical hydrogen storage systems has led to the development of a mixed endothermic–exothermic carrier system. Herein we further investigate the factors affecting the dehydrogenation rate of these carriers. A range of heterogeneous catalysts was synthesized via sol–gel methodology and their activity for indoline dehydrogenation was assessed. Metals used included Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt. SiO₂, Al₂O₃, TiO₂ and ZrO₂ were used as supports and Pd/SiO₂ gave the highest conversion over a fixed time. A marked increase in the rate of indoline dehydrogenation was observed when the temperature was increased between 100 and 180 °C, with measured first order rate constants of 1.8 × 10⁻⁴ s⁻¹ at 100 °C and 5.9 × 10⁻⁴ at 120 °C. Although piperidines dehydrogenate more slowly than indolines, steric hindrance around the nitrogen atom in piperidine increases its dehydrogenation rate significantly.