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Although the catalytic performance of boron-containing Ti-MWW (B-Ti-MWW) zeolite can be greatly improved by acid treatment before calcination, there are still issues about the definite role of acid treatment and the evolution of titanium species during post-treatment of B-Ti-MWW not very clear due to the lack of advanced technique to thoroughly characterize titanium species. Herein, powerful UV resonance Raman spectroscopy excited at 244 nm was used to address these issues for the first time. It was surprisingly found out that acid treatment of as-synthesized B-Ti-MWW not only removed about half of the absolutely dominant non-framework TiO 6 species but also made the other part converted into framework TiO 4 species, which has never been reported before. While acid treatment of directly calcined B-Ti-MWW made most of the dominant non-framework TiO 6 species transformed into anatase TiO 2 . Importantly, among all treated samples, only those obtained from acid treatment of as-synthesized B-Ti-MWW and subsequent calcination showed catalytic activity in 1-hexene epoxidation, fully demonstrating that the remarkable enhancement of catalytic performance by acid treatment before calcination was actually ascribed to the transformation of inactive non-framework TiO 6 species into active framework TiO 4 species. These understandings would be very helpful for the study of boron-containing titanosilicate zeolites. [ABSTRACT FROM AUTHOR]

UV Raman spectroscopy has been demonstrated to be a powerful technique in catalysis because it can avoid the fluorescence interference occurring in visible Raman spectroscopy and concurrently enhance the Raman scattering intensity owing to the short wavelength of the excitation laser and resonance Raman effect. This article briefly reviews the recent advances in the study on heterogeneous catalysis by UV Raman spectroscopy, including the identification of isolated transition metal ions in molecular sieves, in situ study of zeolite assembly mechanisms and catalytic reaction mechanisms, and the monitoring of the surface phase transformation of metal oxide photocatalysts. UV (resonance) Raman spectroscopy, with the power of resonance enhancement for Raman signal and the advantage of high sensitivity for surface structure, coupling with in situ methodology, can provide the information about the active sites/phase and their assembling mechanisms, which are helpful for the understanding of heterogeneous catalysis and the rational design of highly active and selective catalysts. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ti-MWW zeolite has attracted much attention because of its excellent catalytic oxidation performance. As one of the essential components in zeolites, phosphorus (P) has been widely used for modification to enhance the hydrothermal stability and catalytic performance of aluminosilicate zeolite. Herein, a series of P-modified Ti-MWW zeolite samples were prepared with a simple way by directly adding various amounts of phosphoric acid into the acid-treated system. The effect of P modification on both structure and catalytic performance of Ti-MWW zeolite was systematically investigated. We demonstrated that some highly active framework TiO 4 * species with Ti–O–P structure are formed after modification with moderate P, leading to the remarkable improvement of catalytic activity in 1-hexene epoxidation. While introducing excess amounts of phosphoric acid would result in the formation of much inactive titanium phosphate species, which block the channels and finally decrease the catalytic performance significantly. Density functional theory calculations confirmed that the new formed Ti–H 2 PO 4 site is more active than the Ti–OH site in Ti-MWW zeolite for model propene epoxidation, revealing the promotional effect of P modification. This work would deepen our understanding of P modification at the atomic level and benefit to improve the catalytic performance of titanosilicate zeolite. [Display omitted] • Effect of P modification on the structure and catalytic performance of Ti-MWW zeolite was studied. • Some highly active framework TiO 4 * species was formed when modified with moderate phosphoric acid. • P Modification with large amounts was detrimental to epoxidation due to formation of inactive titanium phosphate species. [ABSTRACT FROM AUTHOR]