Effect of Pr in CO₂ Methanation Ru/CeO₂ Catalysts

Abstract

CO 2 methanation has been studied with Pr-doped Ru/ CeO 2 catalysts, and a dual effect of Pr has been observed. For low Pr content (i.e., 3 wt %) a positive effect in oxygen mobility prevails, while for high Pr doping (i.e., 25 wt %) a negative effect in the Ru−CeO 2 interaction is more relevant. Isotopic experiments evidenced that Pr hinders the dissociation of CO 2 , which takes place at the Ru−CeO 2 interface. However, once the temperature is high enough (200 °C), Pr improves the oxygen mobility in the CeO 2 support, and this enhances CO 2 dissociation because the oxygen atoms left are delivered faster to the support sink and the dissociation sites at the interface are cleaned up faster. In situ Raman spectroscopy experiments confirmed that Pr improves the creation of oxygen vacancies on the ceria lattice but hinders their reoxidation by CO 2 , and both opposite effects reach an optimum balance for 3 wt % Pr doping. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments showed that Pr doping, regardless of the amount, decreases the population of surface carbon species created on the catalysts surface upon CO 2 chemisorption under methanation reaction conditions, affecting both productive reaction intermediates (formates and carbonyls) and unproductive carbonates.

Probing the Actual Role and Activity of Oxygen Vacancies in Toluene Catalytic Oxidation: Evidence from In Situ XPS/NEXAFS and DFT +UCalculation

“…Furthermore, the subsurface Ce 3+ proportion also increases from ∼3.2 to ∼10.7%, suggesting that the migratable lattice oxygen in the subsurface can be transmitted to the surface and serve as a supplement of O ads to oxidize toluene. This process proves the crucial role of oxygen vacancies in oxygen species diffusion and subsurface storage, essentially contributing to the OSC property of CeO 2 -based catalysts. , …”

“…This process proves the crucial role of oxygen vacancies in oxygen species diffusion and subsurface storage, essentially contributing to the OSC property of CeO 2 -based catalysts. 61,62 Besides inducing the electron deficit and tensile-strained lattice, cobalt doping also increases the activity of oxygen vacancies, both directly and indirectly. On the one hand, cobalt can act as an electron reservoir and form an asymmetric oxygen vacancy to directly participate in redox reactions.…”

Niobium Modification of CeO2 Tuning Electron Density of Nickel–Ceria Interfacial Sites for Enhanced CO2 Methanation

“…Additionally, the interaction between Ni and NbCe enhances the electron transfer to the active sites on the NiCe surface, optimizing the electronic properties of the Ni cluster and Ni−Ce interface and thereby improving the CO 2 methanation activity of the catalyst. 21,33,45 Textural parameters were also determined by nitrogen physisorption (Figure S5). Ni/10NbCe exhibits nearly the same BET surface area (87 m 2 /g) as Ni/Ce (90 m 2 /g), which had no contribution to the CO 2 methanation.…”

“…This difference indicates that the Nb 5+ has been successfully incorporated into the CeO 2 lattice, resulting in the formation of a Nb–Ce–O solid solution, therefore changing the electronic state of the Nb element. , This results in an increase in the conduction band electron concentration within the carrier. Additionally, the interaction between Ni and NbCe enhances the electron transfer to the active sites on the NiCe surface, optimizing the electronic properties of the Ni cluster and Ni–Ce interface and thereby improving the CO 2 methanation activity of the catalyst. ,, Textural parameters were also determined by nitrogen physisorption (Figure S5). Ni/10NbCe exhibits nearly the same BET surface area (87 m 2 /g) as Ni/Ce (90 m 2 /g), which had no contribution to the CO 2 methanation.…”

Progress in reaction mechanisms and catalyst development of ceria-based catalysts for low-temperature CO2methanation

“…10II). In addition, López-Rodríguez et al 150 found the dual effect of Pr on CO 2 methanation over Ru/CeO 2 catalysts. Specifically, a Ru/CeO 2 sample with low Pr content (∼3 wt%) exhibited a relatively high CO 2 conversion of ∼55% at 270 °C due to a positive effect in oxygen mobility induced by Pr.…”