The evolutions of carbon and iron species modified by Na and their tuning effect on the hydrogenation of CO2 to olefins

Abstract

This study unravels the effect of Na promoter on the distribution of surface carbon species and the regulation of the chemical and structural evolution of Fe nanoparticles through in situ technologies, and illustrates the modification of carbon and iron species for olefins formation during CO2 hydrogenation. With the contents of Na promoter increasing from 0 wt% to 0.5 wt%, the ratio of olefins to paraffins ranging from C2-C7 rose greatly from 0.70 to 5.67. The increase in the density of Na on the Fe5C2 surface improved the stability of Fe5C2 by suppressing the further hydrogenation of Fe5C2, which could be directly confirmed by that the Fe5C2 cannot be reduced by H2 (450 °C, 0.1 MPa, 2 h) with the content of Na increasing of from 0% to 0.5%. In situ Raman spectra and temperature programed profiles have demonstrated that the presence of Na promoter has also proved to facilitate the carbon deposits by dissociation of CO and inhibit the reduction of surface carbon species by H2 (350 °C, 0.1 MPa, 6 h). Consequently, the formation of olefins was enhanced by the inhibition hydrogenation of intermediate carbon species.