Abstract
CO2 methanation is typically carried out using Ni-supported catalysts containing promoters such as alkali or alkali-earth metals to improve their properties. In this work, bimetallic Ni-based USY zeolite catalysts containing alkali (Li, K and Cs) and alkali-earth (Mg, Ca) metal compounds were prepared using the same conditions (15 wt% of metals; co-impregnation), characterized by N2 sorption, XRD, TGA, CO2 adsorption–desorption, DRS UV-Vis and H2-TPR, and finally applied in CO2 methanation reaction (86,100 mL h−1 g−1, PCO2 = 0.16 bar, H2:CO2 = 4:1). For each group, the effects of the second metal nature on the properties and performances were assessed. Alkali metals incorporation induced considerably low catalytic performances (CH4 yields < 26%), attributed to their negative impact on zeolite structure preservation. On the contrary, alkali-earth metal-containing catalysts exhibited lower structural damage. However, the formation of Ni-Mg mixed oxides in Ni-Mg/USY catalyst and CaCO3 during the reaction in Ni-Ca/USY sample could explain their performances, similar or lower than those obtained for Ni/USY catalyst. Among the studied metals, calcium was identified as the most interesting (CH4 yield of 65% at 415 °C), which was ascribed to the slight improvement of the Ni0 dispersion.
Highlights
CO2 methanation, an important reaction in the current context of renewable energies expansion [1,2], is typically carried out using metal-supported catalysts [3,4,5,6,7,8,9,10]
The incorporation of alkali metals together with Ni led to non-porous materials isotherms with a drastic reduction of the Vmicro, Vmeso and Sext, suggesting the damage and/or collapse of the zeolite structure [22,23]
The results suggest the occurrence of sintering or agglomeration of metal particles in the case of Ni-Li/USY catalyst (∆dNi0 = 4 nm)
Summary
CO2 methanation, an important reaction in the current context of renewable energies expansion [1,2], is typically carried out using metal-supported catalysts [3,4,5,6,7,8,9,10]. Despite being one of the most used metals, the utilization of nickel as active metal still requires solutions to some problems such as sintering, reoxidation, carbon deposition and sulfur poisoning [11] In this way, the nature and properties of the chosen support can influence the metallic dispersion, the electronic properties and play an important role in the activation of CO2 and, in their catalytic performance and stability. The incorporation of rare-earth metal oxides (e.g., CeO2, La2O, Y2O3) is a common strategy to improve the properties of Ni catalysts. Their high cost and limited availability requires the identification of alternative promoters
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