Zeolite 13X and 5A were modified with nickel using three different methods: evaporation impregnation, deposition precipitation, and ion-exchange for comparison in CO₂ methanation. The catalysts were tested in a lab scale fixed bed reactor and their physico-chemical properties were characterized by XRD, SEM-EDX, TEM, STEM-EDX, nitrogen physisorption, H₂-TPR and NH₃-TPD. The physico-chemical characterization results of Ni modified 13X and 5A zeolite catalysts showed that the zeolite structure did not change after the Ni modification by different catalyst synthesis methods, although the surface area and micro-pore volume decreased. The average diameter of NiO and the NiO cluster size range of Ni zeolite catalyst synthesized with ion exchange are smaller than the catalysts prepared by the evaporation impregnation and deposition preparation. Ni dispersed well through 13X, while a lot of Ni appeared on the crystal outer surface of 5A zeolite. Evaporation impregnation and deposition precipitation prepared Ni13X catalysts exhibited a higher activity than ion-exchange prepared samples on CO₂ methanation. The catalyst performance of Ni5A-IE and Ni13X-IE zeolite catalysts, which were synthesized using the ion-exchange method for CO₂ methanation was limited by the actual loading of Ni. The Ni 13X catalysts have less CH₄ selectivity which could be attributed to their lower acidity. Ni13X-EIM catalyst showed good catalytic stability at 360 °C, with no catalyst deactivation during a 200 h catalyst stability test.

Hydrogen produced by the electrolysis of water using sustainable electricity will play an increasingly important role as an energy and a feedstock vector. Shifting from fossil to renewable resources means that new industrial platforms have to be set up to provide carbon-based fuels and bulk base chemicals to replace the current fossil resources based routes. The global demand cannot be met by indirect use of carbon dioxide via biomass necessitating the use from point sources or direct air capture, which changes the value of CO2 from waste to commodity chemicals. The production of chemicals by hydrogenation of CO2 is typically hampered by the thermodynamic conversion being far from 100% under currently viable reaction conditions. The equilibrium can, however, be shifted to increase conversion by removing one of the reaction products, namely water, from the reaction mixture with sorbents like zeolites. Prerequisite to conversion enhancement and process intensification is the close proximity of sorption and catalytic sites. This review presents the state of the art in synthesis and application of these, in fact, bifunctional materials.

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.