The impact of nitrogen-containing compounds on the S-vacancies over the iron-based catalysts for direct coal liquefaction during the pre-sulfurization process

To advance the direct coal liquefaction (DCL) technology by a “Catalytic cycle of hydrogen donor solvents” pathway, it was   important   for the iron-based DCL catalyst to be pre-sulfurized under a suitable condition. In this report, the effect of liquid medium in the slurry bed pre-sulfurization process on iron-based catalyst was studied. Catalysts were pre-sulfurized under a variety of liquid mediums including alkanes, aromatics and heteroatom-containing compounds and the activity were evaluated according to their performance on hydrogenation of naphthalene . It was observed that, the nitrogen-containing medium give rise to the significant negative influence on the catalytic activity (with only 2.5 %-15.3 % of naphthalene conversions). Multiple spectroscopic and microscopic analyses of catalysts exhibited that the decrease of S vacancies was mainly responsible for the low activity. It was due to the promotion effect on Fe 1-x S crystallization and troilite generation. S vacancies of the iron-based catalysts was considered as Lewis acid sites to catalyze the hydrogenation reaction. The new findings from this work is beneficial for the development and optimization of pre-sulfurization technology .