Versatile aerosol-assisted sol-gel synthesis of mesoporous metal-promoted silica: The role of metal promoters in enhancing CO2 methanation over Ru catalysts
(2024) Spray-Drying Symposium — Location: Würzburg, Germany (8.April.2024)
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- The catalytic conversion of CO2 with green H2 to produce CH4 (CO2 methanation) is one of the promising strategies helping to mitigate the anthropogenic CO2 emission and utilizing the surplus green electricity (Power-to-Gas scenario) [1]. In the literature, Ru-based catalysts are known to be the most active and selective for the methanation reaction. Their performance is typically governed by nanoscale properties, such as Ru nanoparticle shape and size, structural/electronic metal-support interaction, and promoter/doping effect [1, 2]. In general, silica-supported methanation catalysts are only moderately active owing to the weak metal-support interaction and the absences of intrinsic chemical effect (e.g., oxygen vacancies and basicity) and electronic effect [3]. This work aims to investigate the role of metal promoters in silica-supported Ru catalysts for enhanced CO2 methanation. We focus on different transition metals (4%M-SiO2 where M = Ti, Zr, Nb, or V) and different loadings of the best promoter (x%V-SiO2 where x = 4, 8, 12 or 16%) to elucidate – at the molecular level – the effects on the catalyst properties and performance. To do so, the versatile aerosol-assisted sol-gel process has been leveraged for the preparation of mesoporous metal-promoted silica support materials. This process integrates sol-gel chemistry, aerosol spray drying and evaporation-induced self-assembly in one step and continuous mode of rapid production. It also offers a possibility to incorporate a variety of metals into silica supports [4]. Herein, tetraethyl orthosilicate, metal alkoxide (titanium butoxide, zirconium butoxide, niobium n-butoxide, or vanadium triisopropoxide), tetrapropylammonium hydroxide, and F127 surfactant were first vigorously mixed to prepare the precursor solution, which was then atomized into small droplets and carried by air through the drying chamber. Under these conditions, solvent evaporation induced self-assembly of F127 surfactant leads to micelles around which polycondensation of inorganic gel quickly occurs. The dried solid microspheres of metal-promoted silica materials were collected and calcined prior to the wetness impregnation with RuO2 nanoparticles (nominal 2 wt% Ru) to prepare Ru-based catalysts. The unpromoted SiO2 and 4%metal-promoted SiO2 possess a spherical morphology (Figure 1(a)) with high specific surface area (590-670 m2/g). It is evidenced by means of the XRD and UV-Vis analyses that Ti, Zr, Nb, and V species are highly dispersed in these materials without the formation of crystalline phase. Further increase of V loading up to 16% causes substantial decrease in specific surface area (34 m2/g at 16wt.% of V2O5) and the formation of macropores (Figure 1(b)), which could be accounted for by the buildup of V2O5 crystallites. Strikingly, the catalytic activity over Ru/16%V-SiO2 is highly improved (its methanation rate at 300 C is ca. 6-fold higher than Ru/0%M-SiO2). It is likely that V2O5 in Ru/16%V-SiO2 plays a beneficial role in stabilizing Ru nanoparticles and preventing their aggregation, unlike in the case of unpromoted Ru/0%M-SiO2 (Figure 1). More importantly, V2O5 could provide the interaction between Ru and O-vacancies, facilitating electron transfer from the latter to interfacial Ru sites. From in situ IR experiments, the adsorption and dissociation of CO intermediates appears be promoted on these electronically modified Ru sites at the interface perimeter, thus boosting the methanation activity.
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Hongmanorom, P., & Debecker, D. (2024). Versatile aerosol-assisted sol-gel synthesis of mesoporous metal-promoted silica: The role of metal promoters in enhancing CO2 methanation over Ru catalysts. Spray-Drying Symposium, Würzburg, Germany. https://hdl.handle.net/2078.5/240286