{"title":"In Situ Structure Study of a TiO2 Doped MnOX-Na2WO4/SiO2 Catalyst Under Na2WO4 Melting Conditions","authors":"","doi":"10.1007/s11244-024-01946-4","DOIUrl":null,"url":null,"abstract":"<h3>Abstract</h3> <p>MnO<sub>X</sub>-Na<sub>2</sub>WO<sub>4</sub>/SiO<sub>2</sub> catalyst exhibited notable C<sub>2</sub> selectivity/yield in the oxidative coupling of methane (OCM), a promised green chemistry reaction. Nevertheless, the reaction mechanism of this catalyst remains a subject of contention, particularly regarding the role of Na<sub>2</sub>WO<sub>4</sub> in the activation. In this study, in situ characterizations of a TiO<sub>2</sub>-modified MnO<sub>X</sub>-Na<sub>2</sub>WO<sub>4</sub>/SiO<sub>2</sub> catalyst are conducted by XRD and XPS correlating to the OCM reaction condition, focusing on the simultaneous phase transition of catalyst components within its activation temperature zone. The online MS along with XPS/XRD coupled activity study confirm that transition from Mn<sup>3+</sup> to Mn<sup>2+</sup> stands as a pivotal factor influencing the reactivity. In situ XRD further revealed that in this narrow temperature window there is a particular three-step Na<sub>2</sub>WO<sub>4</sub> phase change, ending as molten salt, right before the substantial Mn<sup>3+</sup> to Mn<sup>2+</sup> transfer initiated. In addition, the rarely observed Na<sub>2</sub>WO<sub>4</sub> behavior as molten salt is observed by in situ XPS with rapid spectra collected during an on-stage heating process. These comprehensive in situ catalyst characterizations, covering the extensive structure–activity relationship from solid state to partial molten salt condition, supply new important evidence of the active oxygen transfer pathway from Na<sub>2</sub>WO<sub>4</sub> to Mn species which provides a key to understand the activation mechanism of MnO<sub>X</sub>-Na<sub>2</sub>WO<sub>4</sub>/SiO<sub>2</sub> catalyst in OCM.</p> <span> <h3>Graphical Abstract</h3> <p> <span> <span> <img alt=\"\" src=\"https://static-content.springer.com/image/MediaObjects/11244_2024_1946_Figa_HTML.png\"/> </span> </span></p> </span>","PeriodicalId":801,"journal":{"name":"Topics in Catalysis","volume":"58 1","pages":""},"PeriodicalIF":2.8000,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Topics in Catalysis","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1007/s11244-024-01946-4","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, APPLIED","Score":null,"Total":0}
引用次数: 0
Abstract
MnOX-Na2WO4/SiO2 catalyst exhibited notable C2 selectivity/yield in the oxidative coupling of methane (OCM), a promised green chemistry reaction. Nevertheless, the reaction mechanism of this catalyst remains a subject of contention, particularly regarding the role of Na2WO4 in the activation. In this study, in situ characterizations of a TiO2-modified MnOX-Na2WO4/SiO2 catalyst are conducted by XRD and XPS correlating to the OCM reaction condition, focusing on the simultaneous phase transition of catalyst components within its activation temperature zone. The online MS along with XPS/XRD coupled activity study confirm that transition from Mn3+ to Mn2+ stands as a pivotal factor influencing the reactivity. In situ XRD further revealed that in this narrow temperature window there is a particular three-step Na2WO4 phase change, ending as molten salt, right before the substantial Mn3+ to Mn2+ transfer initiated. In addition, the rarely observed Na2WO4 behavior as molten salt is observed by in situ XPS with rapid spectra collected during an on-stage heating process. These comprehensive in situ catalyst characterizations, covering the extensive structure–activity relationship from solid state to partial molten salt condition, supply new important evidence of the active oxygen transfer pathway from Na2WO4 to Mn species which provides a key to understand the activation mechanism of MnOX-Na2WO4/SiO2 catalyst in OCM.
期刊介绍：
Topics in Catalysis publishes topical collections in all fields of catalysis which are composed only of invited articles from leading authors. The journal documents today’s emerging and critical trends in all branches of catalysis. Each themed issue is organized by renowned Guest Editors in collaboration with the Editors-in-Chief. Proposals for new topics are welcome and should be submitted directly to the Editors-in-Chief.
The publication of individual uninvited original research articles can be sent to our sister journal Catalysis Letters. This journal aims for rapid publication of high-impact original research articles in all fields of both applied and theoretical catalysis, including heterogeneous, homogeneous and biocatalysis.
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