Catalytic dehydrogenation of liquid organic hydrogen carrier dodecahydro-N-ethylcarbazole over palladium catalysts supported on different supports

The system based on liquid organic hydrogen carrier (LOHC) is one of the technologies to solve the problem of hydrogen storage and transportation capacity in large-scale applications. In this paper, the catalytic dehydrogenation of LOHC dodecahydro-N-ethylcarbazole (H12-NEC) over supported Pd nanoparticles (NPs) catalyst on four kinds of different supports, such as Pd/C, Pd/Al2O3, Pd/TiO2, and Pd/SiO2, was studied. It was found from catalyst characterization and dehydrogenation reaction that the volcano-type dependence of the activity on the Pd particle size, catalytic activity improvement with large specific surface area, and high Pd reduction degree indicated that the structure, particle size, and reduction degree of Pd NPs and textural properties of supports had a synergistic effect on the catalytic performance. Among all the catalysts, Pd/C displayed outstanding catalytic performance with the H12-NEC conversion of 99.9% and hydrogen storage capacity of 5.69 wt% at 180 °C after 12 h. The particle size of Pd/C distributes in the range of 1.5–6.0 nm with an average size of 3.0 nm. The results of dehydrogenation reaction kinetics showed that the rate limiting step and rate constant for different catalysts were mainly related to the physicochemical properties and adsorption and activation abilities towards the reactants and intermediates. In terms of the stationarity of dehydrogenation process, Pd/Al2O3 was excellent, indicating that it was best for dehydrogenation of H12-NEC.