Directional introduction of pyridine nitrogen functional groups in activated carbon catalysts for the catalytic production of hydrogen: An experimental and DFT calculation

Abstract

With the increase in global energy consumption, it has become difficult for traditional energy (re)sources to meet our basic needs. Hydrogen energy is an important component of a low-carbon or carbon-free energy strategy, and the thermochemical sulfur-iodine cycle is considered to be one of the most promising methods for hydrogen production. Nitrogen-doped activated carbon catalysts (NACCs) can improve the decomposition efficiency of hydrogen iodide (HI). However, the investigation of the active nitrogen-containing functional group (NFG) is still in progress. In this study, results from experiments and density functional theory (DFT) calculations were combined to achieve a pyridine nitrogen targeted modification, with the idea that pyridine nitrogen is the catalytically active center.Using ammonia-carbon dioxide co-activation, the samples contained a maximum of 7.79 % N content, and 77.28 % pyridine nitrogen content. An increase in the pyridine nitrogen content resulted in an increase in the catalytic decomposition efficiency. Bipyridine was used to increase the pyridine nitrogen content to complement the nitrogen-modulation mechanism. The N-6 content reached a maximum when the bipyridine solution concentration was in the range of 0.3–0.35 g/L; this resulted in the highest catalytic efficiency. The transition state and reaction path energies were calculated at the B3LYP/def2-TZVP level and combined with thermodynamic enthalpy correction quantities to improve accuracy. According to the DFT calculations, the models for pyridine nitrogen substitution all reduced the activation energy of HI decomposition reaction compared to the other models.