Revealing the mechanism of Ce promoter in modulating product distribution of CO2 hydrogenation over Fe-based catalysts

Abstract

This study elucidates the influence of the Ce promoter on the structure and surface intermediates of Fe-based catalysts and provides insights into the mechanism controlling the distribution of CO2 hydrogenation products. The product distribution revealed a volcano-shaped trend for the selectivity of light olefins and C5+ products as the Ce content increased from 0 to 10 wt%, whereas the selectivity for CH4 shows an inverted volcano-shaped trend. Concurrently, the selectivity for CO gradually increased from 14.4 % to 58.8 %. When the Ce content was 1 wt%, the selectivity for light olefins and C5+ products reached maximum values of 41.4 % and 19.1 %, respectively, and the selectivity for methane decreased to 34.3 %. Characterization by in situ X-ray diffraction (XRD), in situ infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS) techniques demonstrated that the variation in product distribution could be attributed to the altered ratio of Fe3O4 to Fe5C2 species, surface enrichment of the Na promoter, and generation and desorption of surface intermediate species induced by the Ce promoter. These factors affect the rate of the reverse water gas shift reaction (RWGS) and the subsequent Fischer-Tropsch (FT) reaction, thereby modulating the product distribution. Understanding the regulation mechanism of the CO2 hydrogenation product distribution by the Ce promoter is expected to provide valuable insights for guiding the design of catalyst structures.