Mechanism of hydrogenation of CO to aromatics from coal pyrolysis gas of low rank under methanol atmosphere

Because there were much more oxygen-containing functional groups for low-rank coal, a large amount of CO and CO₂ were produced during the pyrolysis process. Catalytic hydrogenation of CO or CO₂ to light aromatics could be realized by supplying active hydrogen from methanol. Density functional theory (DFT) was used to investigate the mechanism of CO hydrogenation to aromatics via olefins intermediates over Fe/HZSM-5 catalyst under methanol atmosphere. The results showed that light olefins were formed by CO hydrogenation on Fe₅C₂ (510) surface. C−C bond coupling and chain propagation were achieved through multiple processes such as methylation and deprotonation. Methylation required a high activation energy among these processes. The aromatization of \rmC^+_6 to benzene was carried out by reactions of hydrogen transfer, deprotonation and cyclization. Hydrogen transfer was the most difficult to happen. In the whole process of CO hydrogenation to aromatics, the energy barrier of methylation was the highest, which was the rate-determining step.