Synthesis of Ce₂Sn₂O₇ pyrochlore and Ce₂Sn₂O_8+x solid solution to support FeO_x for simultaneous NH₃-SCR and CO oxidation: Study on the paramorphism effect

Abstract

Paramorphism effect could be an effective strategy to design efficient catalysts, but has been rarely explored. In this study, to achieve efficient catalysts for elimination of NO and CO together, Ce₂Sn₂O₇ pyrochlore and Ce₂Sn₂O_8+x solid solution paramorphs were purposely synthesized to support FeO_x. It is found that Fe/Ce₂Sn₂O₇ displays better reaction performance than Fe/Ce₂Sn₂O_8+x. H₂-TPR results have demonstrated that the dispersed FeO_x has differed interaction with the two types of supports. Electron paramagnetic resonance (EPR) and density functional theory (DFT) calculation have testified that it is easier to generate surface vacancies on Fe/Ce₂Sn₂O₇ than on Fe/Ce₂Sn₂O_8+x, thus forming more abundant active oxygen sites. Furthermore, the total number of Lewis and Brønsted sites on Fe/Ce₂Sn₂O₇ is larger. In addition, reactive NH₄+ linked to Brønsted acidic sites and bridge nitrite are uniquely formed on Fe/Ce₂Sn₂O₇, thus leading to its much better performance than on Fe/Ce₂Sn₂O_8+x. Notably, Fe/Ce₂Sn₂O₇ also exhibits better sulfur and water tolerance. On both catalysts, the NH₃-selective catalytic reduction (NH₃-SCR) reaction obeys a Langmuir-Hinshelwood pathway, while the CO oxidation follows a Mars-van Krevelen mechanism. In summary, a paramorphism effect is obviously observed, which could give people some new thoughts to design high-performance catalysts.

Keywords

NH₃-SCR / CO oxidation / Ce-Sn complex oxide supports / paramorphism effect / FeO_x-support interaction / engineering surface defects

Authors contribution

Yang Y: Data curation, formal analysis, investigation, methodology, writing-original draft, funding acquisition. Song T: Data curation, formal analysis, investigation, methodology, visualization, writing-original draft. Ma J, Zhang S: Investigation, formal analysis, methodology, validation. Huang J: Investigation, formal analysis. Shen J: Investigation, formal analysis, funding acquisition. Xu X: Project administration, resources, software. Xu J: Formal analysis, project administration, methodology, software, resources. Fang X: Project administration, resources. Wang X: Conceptualization, data curation, formal analysis, funding acquisition, validation, project administration, supervision, writing-review & editing

Conflicts of interest

The authors declare no conflicts of interest.

Ethical approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Availability of data and materials

All data generated or analyzed during this study are included in this article and its supplementary information files.

Funding

The authors acknowledge deeply the financial supporting by the National Natural Science Foundation of China (Grant No. 22376090, 22362026, 22172071), the Natural Science Foundation of Jiangxi Province (Grant No. 20242BAB26029), the Key Laboratory Foundation of Jiangxi Province for Environment and Energy Catalysis (Grant No. 20242BCC32041), and the Graduate Students Innovation Special Foundation of Jiangxi Province (Grant No. YC2024-B011).

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