High-Concentration N Vacancy of S-Doped C3N4 Regulates the Electronic Structure of Pd to Promote the Dehydrogenation of Dodecahydro-N-ethylcarbazole

The NECZ/12H-NECZ (N-ethylcarbazole/dodecahydro-N-ethylcarbazole) system is one of the commercially promising liquid organic hydrogen carriers (LOHCs). However, the dehydrogenation reaction of 12H-NECZ is still the bottleneck of the whole hydrogen storage and release process, possessing a relatively low hydrogen release rate. In this study, one kind of C3N4 (carbon nitride) mesoporous nanosheet material with abundant N vacancies was fabricated by the thermal treatment of trace S-doped C3N4, and a series of Pd-based catalysts were prepared by the impregnation reduction method. The Pd/S0.03-C3N4-Nv550 (treated by S-doped and N) catalyst with abundant N vacancies showcases the most outstanding catalytic performance, achieving a 5.41 wt % hydrogen release amount as well as 81.09% NECZ selectivity at 90 min. Combined with the experimental and computational results, the presence of trace S does not lead to structural collapse of the material and interestingly induces the generation of high concentrations of N vacancies. The N vacancies greatly facilitate the dispersion of loaded metals, offering more active sites; meanwhile, the existence of N vacancy weakens the electronic localization of C3N4 carriers, modulates the electronic structure of active metal Pd, and promotes the activation of reactants and intermediates. What is more, the Pd/S0.03-C3N4-Nv550 catalyst shows excellent stability during long-term cycle tests. It provides some reference values for the design of LOHC dehydrogenation catalysts.