Elucidating the effect of sodium on the carburization behaviors of α-Fe under CO or C2H4

Here, we provide an in-depth understanding of the catalytic mechanism of sodium for the carburization of α-Fe catalyst by C2H4 in contrast to traditional CO through an approach combing in situ XRD and molecular orbital theory, considering the carburization of iron-based catalyst to active iron carbides is a prerequisite step to display activity in CO/CO2 hydrogenation. In situ XRD experiments show that sodium can trigger the carburization of α-Fe by CO and accelerate the accumulation of carbon-rich iron carbides, due to the enhanced electron back-donation from d band in Fe surface to 2π* orbitals in CO, thereby facilitating the dissociation of CO and the carburization by CO. Nevertheless, sodium shows a contrary effect on the carburization of α-Fe under C2H4, due to the significant increase of the total dissociative energy, thereby facilitating the desorption instead of dissociation of C2H4 on Fe surface, finally inhibiting the carburization.