Search Results (4)

The activity of Co- and Ni-containing ceria-based catalysts for water–gas shift (WGS) reaction were examined in this work. The catalysts were prepared by the urea co-precipitation method. Sm and Pr dopant (5 wt.%) was used as a structural stabilizer of CeO₂, while Co or Ni was used in a small amount (1 wt.%). H₂-TPR experiments indicate that both Sm and Pr addition increased the reducibility of CeO₂. Among the studies’ catalysts, 1%Ni/Ce5%SmO exhibited the highest WGS activity. In addition, WGS rate was measured in the temperature range of 200–400 °C for Ni supported on CeO₂, Ce5%SmO, and Ce5%PrO. The activation energy of the reaction over 1%Ni/Ce5%SmO was 57 kJ/mol, while it was 61 and 66 kJ/mol, respectively, over 1%Ni/Ce5%PrO and 1%Ni/CeO₂ catalysts. A WGS reaction mechanism, CO adsorbed on the metal cluster is oxidized by oxygen supplied from the CeO₂ support at the metal–ceria interface. This oxygen is then re-oxidized by H₂O, which caps the oxygen vacancy on the ceria surface, and thereby oxygen vacancies serve as active sites for the WGS reaction. Raman experiments indicate that the presence of Sm in 1%Ni/Ce5%SmO catalyst promoted the formation of oxygen vacancies, leading to enhanced WGS performance. Full article

The aim of this work is the development of a structured catalyst for the dry reforming of biogas to be used as a pre–reformer in the indirect internal reforming configuration (IIR) of solid oxide fuel cells (SOFCs). The structured catalyst is based on NiCrAl foams coated with ruthenium (nominal loading 3.0 wt%) supported on a CaZr_0.85Sm_0.15O_3−δ (CZS) perovskite oxide. The powder is produced by solution combustion synthesis and deposited on metallic foams by the wash–coating method. Catalytic tests for the dry reforming of methane (DRM) reaction are carried out at 850 °C, 700 °C and 550 °C for an overall 50 h with CH₄/CO₂ = 1 and p = 1.3 bar at different gas hourly space velocities (GHSVs). The final goal is a proof–of–concept: a laboratory validation of an IIR–SOFC fed by biogas. The carbon amount on spent structured catalysts is evaluated by thermogravimetric analysis and microstructural/compositional investigation. Full article

Water–gas shift (WGS) reaction was performed over 5% Ni/CeO₂, 5% Ni/Ce-5% Sm-O, 5% Ni/Ce-5% Gd-O, 1% Re 4% Ni/Ce-5% Sm-O and 1% Re 4% Ni/Ce-5% Gd-O catalysts to reduce CO concentration and produce extra hydrogen. CeO₂ and M-doped ceria (M = Sm and Gd) were prepared using a combustion method, and then nickel and rhenium were added onto the mixed oxide supports using an impregnation method. The influence of rhenium, samarium and gadolinium on the structural and redox properties of materials that have an effect on their water–gas shift activities was investigated. It was found that the addition of samarium and gadolinium into Ni/CeO₂ enhances the surface area, reduces the crystallite size of CeO₂, increases oxygen vacancy concentration and improves Ni dispersion on the CeO₂ surface. Moreover, the addition of rhenium leads to an increase in the WGS activity of Ni/CeMO (M = Sm and Gd) catalysts. The results indicate that 1% Re 4% Ni/Ce-5% Sm-O presents the greatest WGS activity, with the maximum of 97% carbon monoxide conversion at 350 °C. An increase in the dispersion and surface area of metallic nickel in this catalyst results in the facilitation of the reactant CO adsorption. The result of X-ray absorption near-edge structure (XANES) analysis suggests that Sm and Re in 1% Re 4% Ni/Ce-5% Sm-O catalyst donate some electrons to CeO₂, resulting in a decrease in the oxidation state of cerium. The occurrence of more Ce³⁺ at the CeO₂ surface leads to higher oxygen vacancy, which alerts the redox process at the surface, thereby increasing the efficiency of the WGS reaction. Full article

Samarium oxide (Sm₂O₃) is a versatile surface for CO₂ and H₂ interaction and conversion. Samarium oxide-supported Ni, samarium oxide-supported Co-Ni, and samarium oxide-supported Ru-Ni catalysts were tested for CO₂ methanation and were characterized by X-ray diffraction, nitrogen physisorption, infrared spectroscopy, H₂-temperature programmed reduction, and X-ray photoelectron spectroscopy. Limited H₂ dissociation and widely available surface carbonate and formate species over 20 wt.% Ni, dispersed over Sm₂O₃, resulted in ~98% CH₄ selectivity. The low selectivity for CO could be due to the reforming reaction between CH₄ (methanation product) and CO₂. Co-impregnation of cobalt with nickel over Sm₂O₃ had high surface adsorbed oxygen and higher CO selectivity. On the other hand, co-impregnation of ruthenium and nickel over Sm₂O₃ led to more than one catalytic active site, carbonate species, lack of formate species, and 94% CH₄ selectivity. It indicated the following route of CH₄ synthesis over Ru-Ni/Sm₂O₃; carbonate → unstable formate → CO → CH₄. Full article