A DFT Study of Zigzag Char Model Hydrogasification and the Mechanism of Fe-Catalyzed Hydrogasification: The Effects of Fe Dispersion

The hydrogasification of coal and other carbon-containing materials is a clean and efficient approach to produce CH4 using hydrogen as a gasifying agent. However, the utilization of char was hindered by the low gasification activity due to the complicated thick ring structures and unclear gasification mechanism. This study chose an excellent Fe-based catalyst, referred to in previous results, as a model to obtain the change rule of gasification activity caused by the change in the structure of Fe during gasification. Herein, the mechanisms of char gasification, Fe single-atom catalytic, and Fe4 cluster catalytic gasification were unveiled in depth by Density Functional Theory (DFT). The results demonstrated that the presence of catalyst Fe and Fe4 caused the formation of the CxFe and CxFe4 structures, hence lowering the activation barrier for the ring-opening reaction by 0.63 and 0.75 eV, respectively. Meanwhile, the presence of Fe reduced the activation barrier for the demethylation reaction by 0.41 and 0.53 eV. And, the existence of catalyst Fe altered the most energy-consuming step from the ring-opening reaction to the methyl desorption and ring-closing reaction. Moreover, the presence of catalyst Fe4 lessened the most energy-consuming step by 0.28 eV compared to the absence of a catalyst. Fe single atoms exhibited the best catalytic performance. Interestingly, the agglomeration of Fe altered the gasification reaction path and inhibited the catalytic activity. However, it was still much higher than gasification without a catalyst. This study could shed light on the hydrogasification reaction mechanism.