Lukas Lätsch, Christoph J. Kaul, Alexander V. Yakimov, Rhaínna McEntee, Trees De Baerdemaeker, Andrei-Nicolae Parvulescu, Karsten Seidel, J. Henrique Teles, Christophe Copéret
{"title":"Nature of Reactive Sites in TS-1 from 15N Solid-State NMR and Ti K-Edge X-Ray Absorption Spectroscopic Signatures Upon Pyridine Adsorption","authors":"Lukas Lätsch, Christoph J. Kaul, Alexander V. Yakimov, Rhaínna McEntee, Trees De Baerdemaeker, Andrei-Nicolae Parvulescu, Karsten Seidel, J. Henrique Teles, Christophe Copéret","doi":"10.1021/jacs.4c10604","DOIUrl":null,"url":null,"abstract":"Ti-containing zeotypes, notably titanosilicalite-1 (TS-1), are prominent examples of heterogeneous catalysts that have found applications in selective oxidation processes with hydrogen peroxide. Despite extensive characterization studies including using various probe molecules to interrogate the nature and the local environment of Ti sites, their detailed structure (as well as reactivity) remains elusive. Here, we demonstrate that using low temperature <sup>15</sup>N magic angle spinning (MAS) ssNMR spectroscopy of adsorbed pyridine on TS-1 combined with Ti K-edge XANES on a range of samples (dehydrated, hydrated, contacted with H<sub>2</sub>O<sub>2</sub> and pyridine) provides unique information regarding the Ti sites, highlighting their reactivity and dynamic nature. While dehydrated TS-1 shows only Lewis acid sites, the presence of H<sub>2</sub>O generates Brønsted acid sites, whose amount correlates with water loading. Moreover, the methodology─based on <sup>15</sup>N ssNMR and Ti K-edge XANES─applied to a library of samples with various Ti-loadings and absence of extraframework TiO<sub>2</sub> also enables quantification of the amount of Lewis acid sites and to establish a structure–activity descriptor (ratio of pyridine adsorbed on silanols vs titanium). Complementary analysis including computational modeling reveals that the reaction of Ti sites with H<sub>2</sub>O generates an acidic bridging silanol Ti-(OH)-Si, upon hydrolysis of one Ti–O–Si linkage, where Ti expands its coordination from four to pentacoordinated according to XAS.","PeriodicalId":49,"journal":{"name":"Journal of the American Chemical Society","volume":null,"pages":null},"PeriodicalIF":14.4000,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of the American Chemical Society","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1021/jacs.4c10604","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Ti-containing zeotypes, notably titanosilicalite-1 (TS-1), are prominent examples of heterogeneous catalysts that have found applications in selective oxidation processes with hydrogen peroxide. Despite extensive characterization studies including using various probe molecules to interrogate the nature and the local environment of Ti sites, their detailed structure (as well as reactivity) remains elusive. Here, we demonstrate that using low temperature 15N magic angle spinning (MAS) ssNMR spectroscopy of adsorbed pyridine on TS-1 combined with Ti K-edge XANES on a range of samples (dehydrated, hydrated, contacted with H2O2 and pyridine) provides unique information regarding the Ti sites, highlighting their reactivity and dynamic nature. While dehydrated TS-1 shows only Lewis acid sites, the presence of H2O generates Brønsted acid sites, whose amount correlates with water loading. Moreover, the methodology─based on 15N ssNMR and Ti K-edge XANES─applied to a library of samples with various Ti-loadings and absence of extraframework TiO2 also enables quantification of the amount of Lewis acid sites and to establish a structure–activity descriptor (ratio of pyridine adsorbed on silanols vs titanium). Complementary analysis including computational modeling reveals that the reaction of Ti sites with H2O generates an acidic bridging silanol Ti-(OH)-Si, upon hydrolysis of one Ti–O–Si linkage, where Ti expands its coordination from four to pentacoordinated according to XAS.
期刊介绍:
The flagship journal of the American Chemical Society, known as the Journal of the American Chemical Society (JACS), has been a prestigious publication since its establishment in 1879. It holds a preeminent position in the field of chemistry and related interdisciplinary sciences. JACS is committed to disseminating cutting-edge research papers, covering a wide range of topics, and encompasses approximately 19,000 pages of Articles, Communications, and Perspectives annually. With a weekly publication frequency, JACS plays a vital role in advancing the field of chemistry by providing essential research.