The synergistic effects of promoters on adjusting reaction pathway over iron catalysts for CO2 hydrogenation to CO

Abstract

The reverse water gas shift (RWGS) reaction is a critical and essential step in the CO2 hydrogenation of iron-based catalysts to produce high-value chemicals such as olefins and higher alcohols. Modification iron-based catalysts by promoter is a popular way in design efficient catalysts which not only can regulate the iron active species but also alter the CO2 adsorption and hydrogenation performance of the catalyst. Herein, a series of Na and Pd promoted 10Fe/SiO2 were prepared. 1Pd/2Na10Fe/SiO2 catalyst exhibited the highest CO2 conversion (13.2 %), the highest CO selectivity (99.7 %) and good catalyst stability. Combination of various characterization results, such as XPS, HRTEM, Mössbauer spectroscopy, CO/CO2-TPD, H2-TPD and in situ DRIFTS, it was found that the addition of Na promoter altered the reaction pathway from redox and associated pathway to only following an associative pathway, contributing to the high CO selectivity. Besides, when the content of Fe2+ species was similar, the associated pathway would be advantageous to high CO formation rate during RWGS reaction over iron-based catalysts. On the other hand, in the same reaction pathway, the content of Fe2+ species would determine the CO formation rate over iron-based catalysts during RWGS reaction.