Performance of Reverse Water Gas Shift on Coprecipitated and C‐Templated BaFe‐Hexaaluminate: The Effect of Fe Loading, Texture, and Promotion with K

The effects of chemical composition, texture, and promotion with potassium of coprecipitated and carbon‐templated BaFe‐hexaaluminate catalysts on their performance in reverse water gas shift (RWGS) reaction were studied in a fixed‐bed catalytic reactor at T=350 °C, p=20 bar, H2: CO2 of 3. The methane selectivity at these conditions did not exceed 0.1 %. It was established that the rate of RWGS is strongly affected by the catalysts iron content gradually increasing up to 45 % Fe. Decreasing the catalyst nanocrystals platelets size (diameter/thickness) from 500–800/50–80 nm to 150–250/30–50 nm (SEM) by implementing the CT increased the surface area and the rates of reaction. Modeling of the redox cycle of RWGS by CO2‐TPD, TP reaction and TP reduction indicated that H2 reduction is needed for regeneration of active sites Fe2+ ions associated with oxygen vacancies. Potassium displayed a strong promotion effect on the activity of Ba−Fe‐hexaaluminates. At optimal K content of 6 wt %, the RWGS rates increased by a factor of 12–15 without changing the TOF number. This was attributed to increasing concentration of active sites due to the reduction of Fe3+ ions (XPS). Loading up the iron: it was found that the mechanism based on experimental data includes [Fe2+‐O‐vacancy] pairs on BaFe‐hexaaluminate surface that are oxidized by CO2 to Fe3+ with the release of CO. Reduction of Fe3+ by H2 with the release of H2O regenerates active sites. Fe and K loading as well as the surface area determine the amount of [Fe2+‐O‐vacancy] sites and the catalytic activity.