Ni-Ce/Zeolites for CO2 Hydrogenation to CH4: Effect of the Metal Incorporation Order

The effect of the metal incorporation order used in the preparation of bimetallic ultrastable Y (USY) zeolite catalysts for CO2 methanation has been studied. First, a Na-USY(3) zeolite was impregnated with 5% of Ni and 3% of Ce in three ways: Ni before Ce (Ce/Ni), Ce before Ni (Ni/Ce), and co-impregnation (Ni-Ce). Stronger interactions between Ni and Ce species are established when Ni is incorporated after or simultaneously with Ce, enhancing the reducibility of the Ni species and decreasing the Ni-0 average size to approximately 2.5 nm. However, the CO2 adsorption capacity is smaller for the sample in which Ce is incorporated before Ni. Even though larger Ni-0 particles (13.3 nm) are formed when Ni is impregnated first, a good CO2 adsorption capacity was also observed for this sample. Co impregnation was finally found as the best preparation method, the results being confirmed for an optimized USY catalyst in terms of Ni content, Si/Al ratio, and compensating cation.