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

Abstract

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).

Advances in the Design of Heterogeneous Catalysts and Thermocatalytic Processes for CO2 Utilization

“…76 Although there are only a few examples of iron-based RWGS catalysts reported to date, the potential of some recently reported catalysts was remarkable in terms of both activity and stability. 66,[76][77][78][79] An early report by Weatherbee et al showed that CO can be produced over Fe/SiO2 catalyst in CO2 hydrogenation, but the formation rate was much lower when compared to other transition metals of the same group. 80 Fishman et al obtained 28% CO2 conversion over hematite nanosheets at 510 °C, and 50% CO2 conversion over hematite nanowires at a very high temperature of 750 °C.…”

“…Being the cheapest metal among all transition elements, iron can be a potential replacement of existing RWGS catalysts due to its high oxygen mobility and thermal stability . Although there are only a few examples of iron-based RWGS catalysts reported to date, the potential of some recently reported catalysts was remarkable in terms of both activity and stability. ,− An early report by Weatherbee et al showed that CO can be produced over Fe/SiO 2 catalyst in CO 2 hydrogenation, but the formation rate was much lower when compared with other transition metals of the same group . Fishman et al.…”

La-Doped Alumina, Lanthanum Aluminate, Lanthanum Hexaaluminate, and Related Compounds: A Review Covering Synthesis, Structure, and Practical Importance

“…For instance, in the synthesis procedure known as carbon templating, a carbonaceous support is loaded with the metal containing starting materials (e.g., by impregnation or precipitation). The carbon is finally sacrificed by oxidation, but the high dispersion of the well-mingled ingredients is memorized and favorably influences the formation of the final HA product, resulting in narrow particle sizes, increased surface areas and (where applicable) improved catalytic activities. − The highest surface areas reported for this method are 102 and 105 m 2 /g . For LHA syntheses by this method see Table S1, entries 18–21.…”

“…In this way, the review article by Choudhary et al demonstrates that the optimization of HA catalysts for the combustion of methane and lower alkanes is mainly driven by changing chemical composition, rather than by structural considerations. Another important aspect of catalyst optimization is the influence of the preparation method/condition on catalyst texture and morphology, which, in turn, has an influence on catalyst activity and selectivity. , …”

Recent Advances in Supported Metal Catalysts and Oxide Catalysts for the Reverse Water-Gas Shift Reaction

“…Similarly, the K promoter acts as a reducing agent relative to the Fe metal, and the observed increase in the ratio of the Fe 2+ /Fe 3+ ions over the BaFe-hexaaluminates after the K addition reflects the increasing concentration of reduced Fe 2+ ions in the hexaaluminate lattice, which is accompanied by the appearance of oxygen vacancies due to the cleavage of one of the neighboring Fe-O-M (M = Al, Ba) bonds in the first coordination sphere of Fe ions. These vacancies play a role in the sites for CO 2 adsorption forming monodentate surface carbonates followed by redox transformation evolving CO and leaving the second oxygen bonded to the Fe 3+ ion (Wang et al, 2013b , c ; Utsis et al, 2018 ). The results of DFT calculations demonstrate that the K adatom greatly stabilizes the adsorption of all oxygenate intermediates through direct K-O bonding formation on K-modified Cu(111) and Cu(110) surfaces, thus promoting CO 2 dissociation in the RWGSR.…”