Comparative Studies on Full Dehydrogenation of Dodecahydro-N-Ethylcarbazole on Pd(111) and Ni(111) Surfaces: Mechanism and Catalytic Enhancement

Dodecahydro-N-ethylcarbazole (12H-NEC) is regarded as the most promising liquid organic hydrogen carrier for hydrogen storage and transportation. Understanding the mechanism of 12H-NEC dehydrogenation and developing cost-effective catalysts are significant. Pd is a high-performance catalyst for 12H-NEC but is not cost-effective, and Ni is just the opposite. How to understand the whole process of full dehydrogenation and improve the performance of Ni become two key questions. Herein, we systematically investigated the mechanism of the full dehydrogenation of 12H-NEC on Pd(111) and Ni(111) for the first time. By calculating all the barriers in the whole dehydrogenation process, we identified that 3H-NEC to 2H-NEC is the rate-determining step and Ni is catalytically less effective than Pd, which is attributed to its narrower d-band distribution and a 0.32 eV higher d-band center than that of Pd. To improve the performance of Ni, we further introduced dopants of Au, Ag, Cu, Pd, Pt, Ru, Rh, Zn, and Al. We found that Ag doping brings a downshift of the d-band center from -1.29 to -1.67 eV and reduces the barrier of 4H-NEC to NEC from 0.94 to 0.76 eV. This study provides new insights into the catalytic mechanism and performance-tuning strategy to help future experimental synthesis.