Effect of Different Iron Phases of Fe/SiO2 Catalyst in CO2 Hydrogenation under Mild Conditions

Abstract

The effect of different active phases of Fe/SiO₂ catalyst on the physio-chemical properties and the catalytic performance in CO₂ hydrogenation under mild conditions (at 220 °C under an ambient pressure) was comprehensively studied in this work. The Fe/SiO₂ catalyst was prepared by an incipient wetness impregnation method. Hematite (Fe₂O₃) in the calcined Fe/SiO₂ catalyst was activated by hydrogen, carbon monoxide, and hydrogen followed by carbon monoxide, to form a metallic iron (Fe/SiO₂-h), an iron carbide (Fe/SiO₂-c), and a combination of a metallic iron and an iron carbide (Fe/SiO₂-hc), respectively. All activated catalysts were characterized by XRD, Raman spectroscopy, N₂ adsorption–desorption, H₂-TPR, CO-TPR, H₂-TPD, CO₂-TPD, CO-TPD, NH₃-TPD, and tested in a CO₂ hydrogenation reaction. The different phases of the Fe/SiO₂ catalyst are formed by different activation procedures and different reducing agents (H₂ and CO). Among three different activated catalysts, the Fe/SiO₂-c provides the highest CO₂ hydrogenation performance in terms of maximum CO₂ conversion, as well as the greatest selectivity toward long-chain hydrocarbon products, with the highest chain growth probability of 0.7. This is owing to a better CO₂ and CO adsorption ability and a greater acidity on the carbide form of the Fe/SiO₂-c surface, which are essential properties of catalysts for polymerization in FTs.

The Effect Of Ca Doping On The CO2 Hydrogenation Performance Of CaxZn10‐xFe20 Catalysts (x=0, 0.5, 1 and1.5)

“…Secondly, through CO 2 -TPD, the doping of Ca will weaken the catalyst's basicity but increase the catalyst's basic sites, especially when the Ca doping amount is 1 mmol. The increased basic sites are more conducive to the adsorption of CO 2 , and the red CO 2 in the figure indicates additional CO 2 * Finally, according to the previous literature, [49][50][51] the increase of basic sites benefits the hydrogenation of CO 2 * Therefore, the doping of Ca further improves the performance of the Zn10Fe20 catalyst, and the improvement is most apparent when the doping amount of Ca is 1 mmol.…”

“…It is evident that the Zn10Fe20 catalyst without Ca doping has three desorption peaks at 100, 670, and 790 °C, respectively, corresponding to weak, medium, and strong basic sites. [49] With the doping of Ca, the peak at the weak alkaline site shows an interesting change. On the one hand, the doping of Ca shifted the low-temperature desorption peak to the left, and the less the doping of Ca, the more it moved to the left, which indicated that the doping of Ca further weakened the weak basicity of the Zn10Fe20 catalyst surface.…”

“…The increase in intensity implied a rise in basic sites. [49,50] At the same time, the increase in desorption also means that more CO 2 can be adsorbed under the same conditions so that the surface CO 2 concentration of the catalyst will be relatively higher, which is more favorable for the reverse water gas reaction. [51] In addition to the three desorption peaks at low, medium, and high, a desorption peak also appears at 600 °C with increasing Ca doping, and its intensity increases with increasing Ca doping.…”

“…The intensity of the low‐temperature desorption peak was related to the number of basic sites. The increase in intensity implied a rise in basic sites [49,50] . At the same time, the increase in desorption also means that more CO 2 can be adsorbed under the same conditions so that the surface CO 2 concentration of the catalyst will be relatively higher, which is more favorable for the reverse water gas reaction [51] .…”

Directly Converting CO2 to Light Hydrocarbons on a FeCoAl Prussian Blue Analogue-Based Core–Shell Catalyst via Fischer–Tropsch Synthesis

“…As observed in Figure 2f, all the catalysts show desorption peaks in the temperature range of 350−800 °C in the H 2 -TPD profile, which are assigned to the decomposition of CH species as well as the splitting of OH species. 29,30 The H 2 -TPD pattern of Na/Fe shows three desorption peaks at 403, 562, and 628 °C. The Na/Fe@FeCo-P 0.1 catalyst exhibits higher desorption temperature of H species than Na/Fe, indicating that the introduction of FeCo PBA inhibited the decomposition of CH species.…”