A-site effects of titanate-perovskite (ATiO3)-based catalysts on dehydrogenation of N-heterocyclic molecules

Dehydrogenation reactions in liquid organic hydrogen carrier (LOHC) systems present significant challenges, particularly when aiming for low-temperature operations while ensuring that no hydrogen remains in the sub-strate molecules. Enhancing catalytic performance requires modifying the adsorption behavior of the reactants and products during dehydrogenation. Perovskites have emerged as promising catalyst supports because of their ability to modify the surface chemical properties by manipulating the cations present at the A-and B-sites. This study investigated the effects of A-site cations (Ca, Sr, and Ba) in titanate-type perovskite (ATiO3)-a proto-typical perovskite-on the dehydrogenation activity in LOHC systems. Remarkably, Pd/SrTiO3 exhibited outstanding performance by completely converting octahydro-N-methylindole to N-methylindole and releasing 5.76 wt% hydrogen over 8 h. Additionally, it dehydrogenated dodecahydro-N-ethylcarbazole to N-ethylcarbazole with a hydrogen release of 5.70 wt%. Furthermore, the catalyst demonstrated a stable performance after recy-cling tests for three times without degradation or loss of activity. The chemical state of the catalyst surface was characterized through X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and chemi-sorption using NH3, CO2, and H2. The results revealed that the exceptional dehydrogenation activity of Pd/ SrTiO3 is due to the presence of suitable surface oxygen vacancies and abundant acid-base sites

Reversible Pd Catalysts Supported on Hierarchical Titanate Nanosheets for an <i>N</i>-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 (similar to 1.57 wt %). The single Pd/HTN catalyst successfully accomplished reversible hydrogen storage and release within the LOHC system in one reactor