Sub-nanometer zeolite 13X-supported Ni-ceria catalysts were synthesized for CO₂ methanation. XRD and SEM results show the structure and morphology of 13X zeolite after impregnation and calcination. Ce loading affected the catalysts’ metal dispersion, reducibility, basicity and acidity, and thence their activity and selectivity. STEM-EDX elemental mappings showed that Ce and Ni are predominantly highly dispersed. Ce has a positive effect on the reduction of NiO and leads to a relatively high number of medium basic sites with a low Ce loading. Highly stable 5%Ni2.5%Ce13X had high activity and nearly 100% CH₄ selectivity in CO₂ methanation at 360 °C, which is mainly due to the high dispersion of metals and relatively high amount of medium basic sites. It can be inferred that this catalyst synthesis strategy has great potential for good catalyst dispersion, since metal uptake by the zeolite is selective for the metal citrate complexes in solution.

Zeolite 13X and 5A supported Ni catalysts were synthesized for CO₂ methanation using the evaporation impregnation method. The influence of using different Ni precursors (nitrate, citrate, and acetate) as well as calcination temperatures on the catalyst properties and performance were investigated. XRD, SEM-EDX, TEM, STEM-EDX, N₂ physisorption, H_2-TPR, TPD-NH₃ and TG/DTA were used for detailed characterization of the catalysts. The parent structure of the zeolites did not change during catalyst synthesis. Using nickel citrate and acetate resulted in smaller NiO particle size compared to nitrate. STEM-EDX results showed that all the Ni-precursor complexes entered more efficiently the 13X zeolite structure, which is mainly due to steric hindrance resulting from the smaller pore size of 5A. Methanation experiments revealed that the 13X catalysts synthesized using nickel citrate (5% Ni) displayed clearly higher activity, compared to the catalysts synthesized using nickel nitrate or nickel acetate. A 79% conversion at 320 °C was obtained with 100% selectivity towards CH₄ and the catalyst showed excellent stability during 200 h testing. Overall, it can be concluded that the Ni precursor significantly influences the physico-chemical characteristics and catalytic properties of Ni 13X and Ni 5A zeolite catalysts in CO₂ methanation: complex size and pore size matter.

Zeolites 13X and 5A were modified with nickel and/or ruthenium for CO₂ methanation. The catalysts were prepared by evaporation impregnation and XRD, SEM-EDX, TEM, STEM-EDX, nitrogen physisorption, H₂-TPR and NH₃-TPD were used to characterize the physico-chemical properties of the catalysts. The physico-chemical characterization results show that the zeolites structure did not change after the Ni, Ru modification, however. Ni was able to enter the pores of 13X, in the other case, 5A, an egg shell type structure was formed. Methanation experiments were performed in a lab scale fixed bed reactor system, the results showed that the mono-metallic catalysts out-performed the bi-metallic ones with Ni being the more active. One of the factors influencing the performance of the bi-metallic catalysts was the difficulty to obtain good dispersion when both metals were used. Also the morphology of the catalyst significantly influenced the selectivity. The catalysts with lower weak acidity benefit for getting a higher activity. The single metal catalysts 2.5 %Ru13X and 5%Ni13X showed good catalytic stability with around 97 % CH₄ selectivity at 360 °C, with no catalyst deactivation during the 200 h catalyst stability test.