Synergistic effects of promoters on adjusting the reaction pathway over iron catalysts for CO2 hydrogenation to CO

Abstract

The reverse water–gas shift (RWGS) reaction is an essential step in the CO₂ hydrogenation of iron-based catalysts to produce high-value chemicals such as olefins and higher alcohols. Modification of iron-based catalysts by a promoter is a popular method in the design of efficient catalysts. This strategy can regulate 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 catalysts were prepared. The 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, revealed that addition of the Na promoter altered the reaction pathway from a redox and associated pathway to only an associative pathway, thereby contributing to the high CO selectivity. Besides, when the content of Fe²⁺ species was similar, the associated pathway would be advantageous to a high CO formation rate during the RWGS reaction over iron-based catalysts. Conversely, in the same reaction pathway, the content of Fe²⁺ species would determine the CO formation rate over iron-based catalysts during the RWGS reaction.