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

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.