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On the role of Ce in CO₂ adsorption and activation over lanthanum species.

ABSTRACT: La₂O₃ exhibits good performance for various catalytic applications, such as oxidative coupling of methane (OCM) and dry reforming of methane (DRM), during which coke formation may lead to the deactivation of catalysts. Typically, the reaction between CO₂ adsorbed on La₂O₃ and coke is the rate-determining step of the coke elimination process. This paper describes the influence of Ce addition on the CO₂ adsorption and activation over La₂O₃. Combined with in situ and ex situ characterization and density functional theory (DFT) calculation, we show that Ce addition promotes the formation of bidentate carbonate on La₂O₃via tuning CO₂ adsorption energy. In addition, Ce addition adjusts the ratio of bidentate/monodentate carbonate, and affects the ratio of hexagonal/monoclinic La₂O₂CO₃ on the binary oxides. DRM is used as a probe reaction to examine the coke elimination performance of Ce-La binary oxide. It is found that when the Ce/La ratio reaches the optimal value (0.15), Ce-La binary oxide has the highest CO₂ adsorption energy and predominantly promotes the formation of bidentate carbonate, and hence possesses the highest basicity above 700 °C and finally exhibits the best coke elimination performance.

SUBMITTER: Li X

PROVIDER: S-EPMC5932599 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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On the role of Ce in CO2 adsorption and activation over lanthanum species.

Li Xinyu X Zhao Zhi-Jian ZJ Zeng Liang L Zhao Jiubing J Tian Hao H Chen Sai S Li Kang K Sang Sier S Gong Jinlong J

Chemical science 20180223 14

La2O3 exhibits good performance for various catalytic applications, such as oxidative coupling of methane (OCM) and dry reforming of methane (DRM), during which coke formation may lead to the deactivation of catalysts. Typically, the reaction between CO2 adsorbed on La2O3 and coke is the rate-determining step of the coke elimination process. This paper describes the influence of Ce addition on the CO2 adsorption and activation ove ...[more]

PMID: 29780472

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Project description:Alkyldiamine-functionalized variants of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO2 capture applications owing to their unique step-shaped CO2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary,secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO2 adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg2(dobpdc) and leads to decreased CO2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg2(dotpdc) (dotpdc4- = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg2(pc-dobpdc) (pc-dobpdc4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = para-carboxylate), which, in contrast to Mg2(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg2(pc-dobpdc) with large diamines such as N-(n-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of new adsorbents for carbon capture applications.

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On the role of Ce in CO₂ adsorption and activation over lanthanum species.

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On the role of Ce in CO<sub>2</sub> adsorption and activation over lanthanum species.

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