Reversible Pd Catalysts Supported on Hierarchical Titanate Nanosheets for an N-Methylindole-Based Liquid Organic Hydrogen Carrier

Reversible hydrogenation and dehydrogenation processes were investigated in a liquid organic hydrogen carrier (LOHC) system by employing a single-catalyst approach. Key hydrogen-involved catalytic behaviors, including adsorption and migration, play crucial roles in reactivity. To facilitate these behaviors at the active sites on the catalyst surface during the LOHC process, a defective metal oxide support was utilized. Herein, a Pd catalyst was prepared by using hierarchical titanate nanosheets (HTN) synthesized via solvothermal synthesis. Compared to commercial TiO2 and hierarchical TiO2 (HT), which was synthesized by the calcination of HTN, HTN exhibited a higher density of acidic sites and oxygen vacancies. Density functional theory calculations confirmed that hydrogen spillover occurred more readily on the defective HTN surface than on the TiO2 (101) surface. The Pd/HTN catalyst demonstrated superior catalytic activity for both the hydrogenation and dehydrogenation reactions in the N-methylindole-based LOHC system. The hydrogen uptake of Pd/HTN catalyst (4.73 wt %) was 3 times higher than that of other Pd catalysts (∼1.57 wt %). The single Pd/HTN catalyst successfully accomplished reversible hydrogen storage and release within the LOHC system in one reactor.