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 role of ZrO₂ as different components in Ni-based catalysts for CO₂ reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO₂ as a support using a co-impregnation method. As a promoter (1 wt.% ZrO₂) and a coactive component (10 wt.% ZrO₂), the catalysts with ZrO₂ were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO₂ as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO₂ content, the Ni-ZrO₂ interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO₂ to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO₂ content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO₂ activation-dissociation. The lowest activity (CH₄ conversion ≈ 40% and CO₂ conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO₂ as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO₂ interaction and less oxygen transfer from ZrO₂ to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO₂ interaction on the catalytic activity was deducted by decreasing ZrO₂ content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO₂ provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO₂ for oxygen transfer was successfully developed through a ZrO₂-Al₂O₃ composite. The interaction in this catalyst enhanced the catalytic activity (CH₄ conversion ≈ 54% and CO₂ conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO₂ as a promoter prepared by co-impregnation and with ZrO₂ as a coactive component prepared by a sequential impregnation were tested in combined steam and CO₂ reforming of methane (CSCRM). The results revealed that the ZrO₂ promoter provided a greater carbon resistance (coke = 1.213 mmol·g⁻¹) with the subtraction of CH₄ and CO₂ activities (CH₄ conversion ≈ 28% and CO₂ conversion ≈ %) due to the loss of active sites to the H₂O activation-dissociation. Thus, the H₂O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.

In this paper, the 10 wt% Ni/Al₂O₃-MgO (10Ni/MA), 5 wt% Ni-5 wt% Ce/Al₂O₃-MgO (5Ni5Ce/MA), and 5 wt% Ni-5 wt% Co/Al₂O₃-MgO (5Ni5Co/MA) catalysts were prepared by an impregnation method. The effects of CeO₂ and Co doping on the physicochemical properties of the Ni/Al₂O₃-MgO catalyst were comprehensively studied by N₂ adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature programmed reduction (H₂-TPR), CO₂ temperature programmed reduction (CO₂-TPD), and thermogravimetric analysis (TGA). The effects on catalytic performance for the combined steam and CO₂ reforming of methane with the low steam-to-carbon ratio (S/C ratio) were evaluated at 620 °C under atmospheric pressure. The appearance of CeO₂ and Co enhanced the oxygen species at the surface that decreased the coke deposits from 17% for the Ni/MA catalyst to 11–12% for the 5Ni5Ce/MA and 5Ni5Co/MA catalysts. The oxygen vacancies in the 5Ni5Ce/MA catalyst promoted water activation and dissociation, producing surface oxygen with a relatively high H₂/CO ratio (1.6). With the relatively low H₂/CO ratio (1.3), the oxygen species at the surface was enhanced by CO₂ activation-dissociation via the redox potential in the 5Ni5Co/MA catalyst. The improvement of H₂O and CO₂ dissociative adsorption allowed the 5Ni5Ce/MA and 5Ni5Co/MA catalysts to resist the carbon formation, requiring only a low amount of steam to be added.

Ni-based catalysts have been widely used for the CO₂ reforming of methane (CRM) process, but deactivation is their main problem. This study created an alternative electronic Ni-NiO-CeO₂ interaction on the surface of 5 wt% Ni-5 wt% CeO₂/Al₂O₃-MgO (5Ni5Ce(xh)/MA) catalysts to enhance catalytic potential simultaneously with coke resistance for the CRM process. The Ni-NiO-CeO₂ network was developed on Al₂O₃-MgO through layered double hydroxide synthesis via our ammonia vapor diffusion impregnation method. The physical properties of the fresh catalysts were analyzed employing FESEM, N₂ physisorption, and XRD. The chemical properties on the catalyst surface were analyzed employing H₂-TPR, XPS, H₂-TPD, CO₂-TPD, and O₂-TPD. The CRM performances of reduced catalysts were evaluated at 600 °C under ambient pressure. Carbon deposits on spent catalysts were determined quantitatively and qualitatively by TPO, FESEM, and XRD. Compared to 5 wt% Ni-5 wt% CeO₂/Al₂O₃-MgO prepared by the traditional impregnation method, the electronic interaction of the Ni-NiO-CeO₂ network with the Al₂O₃-MgO support was constructed along the time of ammonia diffusion treatment. The electronic interaction in the Ni-NiO-CeO₂ nanostructure of the treated catalyst develops surface hydroxyl sites with an efficient pathway of OH* and O* transfer that improves catalytic activities and coke oxidation.

This research developed hierarchical 10 wt % Ni-1 wt % ZrO₂/Al₂O₃ catalysts for combined steam and CO₂ reforming of methane (CSCRM) reaction to produce syngas for gas-to-liquid (GTL) application under the ultralow temperature and low steam condition. The hierarchical nanosheet catalysts were prepared via a novel impregnation technique assisted by ammonia vapor diffusion with various times (1, 6, and 12 h) to develop the different magnitude of hierarchical nanosheets on the surface. Then, CSCRM at 600 °C was performed on the catalysts for 6 h. The results evidenced the improvement of H₂ selectivity, reaching an appropriate H₂/CO ratio (1.9-2.0) in FT subunits in the GTL process when nanosheets existed on the surface due to the increase in H₂O adsorption-dissociation sites. The good dispersion of hierarchical nanosheets accompanied by the ZrO₂ promoter successfully enhanced the CH₄ conversion and the coke prevention through the spread nanosheets because of the increase in the number of active sites and the surface interaction. The interaction of hierarchical nanosheets created the H₂O activation-dissociation sites that allowed CO₂ to be selective on the oxygen vacancy sites, producing more OH* and OH* on the catalyst surface to resist the carbon deposition during CSCRM operation.