Tailoring Upsalite-derived Ni-MgO catalysts: Impact of synthesis method on CO2 methanation performance

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CO 2 methanation offers the dual benefits of emission mitigation and energy storage. MgO is considered an ideal support for this process due to its high alkalinity and excellent CO 2 adsorption capacity. In this study, a series of Ni-MgO materials (c.a. 10 wt% Ni) supported on high-surface-area MgO (up to 100 m 2 /g) derived from the thermal treatment of Upsalite® were synthesized using various methods (wet impregnation (WET), incipient wetness impregnation (IWI), and one-pot (OP)) and evaluated for CO 2 methanation. Among them, the catalyst prepared via wet impregnation of mesoporous magnesium carbonate exhibited the highest activity, achieving 86 % CO 2 conversion and 100 % selectivity towards methane at 350 °C. In all cases, the size of the Ni nanoparticles did not increase during the methanation test, even for the longest exposition times, as a result of strong metal–support interactions (SMSI) between Ni and MgO. Ni atom redistribution could be emphasized for Ni-MgO prepared by the IWI and OP methods, leading to smaller particles after the test, but in the end, the best catalyst (WET) was not the one with the smallest Ni nanoparticles but the one showing very constant nanoparticle size throughout methanation. The WET sample was also characterized by the highest percentage of reduced Ni, the highest number of basic sites (CO 2 TPD), and the lowest surface oxygen species (XPS). Furthermore, in situ DRIFTS analyses confirmed that CO 2 methanation over Ni/MgO proceeds via the formate pathway, with HCOO∗ identified as the key intermediate. These results underscore the synergistic effect of Ni nanoparticles and MgO support and provide valuable insights for the rational design of highly efficient Ni-based catalysts for CO 2 methanation. • Ni-MgO solids were synthesized from Upsalite® using 3 approaches. • Ni-MgO from wet impregnation led to the highest activity in methanation. • Strong metal–support interactions ensure abundant active sites and stability. • Ni atoms redistribution was observed for some synthesis approaches. • CO 2 methanation followed the formate pathway (HCOO∗ intermediate).

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