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a b s t r a c tSorption enhanced CO 2 methanation is a complex process in which the key challenge lies in the combined optimization of the catalyst activity and water adsorption properties of the zeolite support. In the present work, improved nickel-based catalysts with an enhanced water uptake capacity were designed and catalytically investigated. Two different zeolite frameworks were considered as supports for nanostructured Ni, and studied with defined operation parameters. 5Ni/13X shows significantly increased, nearly three-fold higher, operation time in the sorption enhanced CO 2 methanation mode compared to the reference 5Ni/5A, likely due to its higher water sorption capacity. Both catalysts yield comparable CO 2 conversion in conventional CO 2 methanation (without water uptake). Regeneration of the catalysts performance is possible via a drying step between methanation cycles under both reducing and oxidizing atmospheres; however, operation time of 5Ni/13X increases further after drying under air.

a This paper presents a proof-of-concept study and demonstrates the next generation of a "smart" catalyst material, applicable to high temperature catalysis and electro-catalysis such as gas processing and as a catalyst for solid oxide cells. A modified citrate-gel technique was developed for the synthesis of La x Sr 1À1.5x Ti 1Ày Ni y O 3Àd . This method allowed the synthesis of single phase materials with a high specific surface area, after the first calcination step at temperatures as low as 650 C. Up to 5 at% of nickel could be incorporated into the perovskite structure at this low calcination temperature. X-ray powder diffraction and microscopy techniques have proven the exsolution of nickel nanoclusters under low oxygen partial pressure. The amount of exsoluted nickel nanoparticles was sensitive to surface finishing, whereby much more exsoluted nanoparticles were observed on pre-treated and polished surfaces as compared to original ones. Increasing A-site deficiency leads to a larger number of nickel particles on the surface, indicating a destabilizing influence of the A-site vacancies on the B-site metal cations.Repetitive redox cycles prove that the nickel exsolution and re-integration is a fully reversible process.These materials working in a cyclic and repetitive way may overcome the drawbacks of currently used conventional catalysts used for high temperature systems and overcome major degradation issues related to catalyst poisoning and coarsening-induced aging.

Perovskite‐type oxides have shown the ability to reversibly segregate precious metals from their structure. This reversible segregation behavior was explored for a commonly used catalyst metal, Ni, to prevent Ni sintering, which is observed on most catalyst support materials. Temperature‐programmed reduction, X‐ray diffraction, X‐ray absorption spectroscopy, electron microscopy, and catalytic activity tests were used to follow the extent of reversible Ni segregation. LaFe1−xNixO3±δ (0≤x≤0.2) was synthesized using a citrate‐based solution process. After reduction at 600 °C, metallic Ni particles were displayed on the perovskite surfaces, which were active towards the hydrogenation of CO2. The overall Ni reducibility was proportional to the Ni content and increased from 35 % for x=0.05 to 50 % for x=0.2. Furthermore, Ni could be reincorporated reversibly into the perovskite lattice during reoxidation at 650 °C. This could be exploited for catalyst regeneration under conditions under which impregnated materials such as Ni/LaFeO3±δ and Ni/Al2O3 suffer from sintering.

Electrochemical performance and degradation was analysed by conductivity measurements as well as thermogravimetric analysis (TGA) under different atmospheres. CO2 was identified as a critical parameter in terms of carbonate formation from Ba0.5Sr0.5Co0.8Fe0.2O3–δ and causes a strong increase in the material resistivity, whereas La0.6Sr0.4Co0.2Fe0.8O3–δ is unaffected. The oxygen exchange kinetic of both compositions is affected by CO2 containing atmospheres.

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