Roles of bridge carbon and heteroatom during the dehydrogenation reaction of dicyclohexylmethane derivatives on Pd and Pt catalysts for liquid organic hydrogen carrier

Liquid organic hydrogen carrier (LOHC) has been developed to overcome the low efficiency of conventional hydrogen storage methods. Although 2-[n-methylbenzyl]pyridine (MBP), one of dicyclohexylmethane derivatives, has been reported as a high-performance LOHC material, its dehydrogenation mechanism has yet to be fully understood. Here, we combine both experiments and theoretical calculations to comparatively elucidate the dehydrogenation mechanism of H12-MBP on Pd and Pt catalysts. The experimental results for hydrogen release from H12-MBP and H6-MBP show that Pd/Al2O3 has a faster initial hydrogen release rate than Pt/Al2O3. Density functional theory calculations reveal that the N-heteroatom in the pyridine ring has a significant effect on the adsorption of H12-MBP. In addition, the hydrogen migration in the pyridine ring serves as the rate-determining step, where the activation free energy of Pd(111) is lower than that of Pt(111). Our results provide insight into the dehydrogenation of heterocyclic compounds with a bridge structure on metal catalysts.