A Thorough Investigation of the Active Titanium Species in TS‐1 Zeolite by In Situ UV Resonance Raman Spectroscopy

Abstract

A thorough investigation of the active titanium species in TS-1 zeolite was conducted by in situ UV resonance Raman spectroscopy combined with UV/Vis diffuse reflectance spectroscopy, DFT calculations, and epoxidation experiments. A new titanium species was identified with a characteristic Raman band at 695 cm(-1) when excited at the 266 nm laser line. It is shown that the newly found titanium species is active in the epoxidation reactions in addition to the tetrahedrally coordinated titanium species. However, the acidity of the new titanium species could catalyze the ring-opening reactions of the epoxy products. It results in a lower selectivity toward the epoxy products relative to that of the tetrahedrally coordinated titanium species. The side reaction can be suppressed by the addition of a weak basic reagent.

UV Raman Spectroscopic Characterization of Catalysts and Catalytic Active Sites

“…Therefore, we proposed the possible pathway during the propylene oxidation on the two kinds of active centers (Fig. 6c) [74]. The finding of TiO 6 species is significant not only for the reveal of the mechanism of side reaction, but also for the improvement of framework titanium amount.…”

“…However, there are still many issues under debate, such as what's the exact nature of the active site [36,37,68,69] and the reaction pathways [70][71][72][73]. Recently, we have conducted a thorough investigation of the active titanium species in TS-1 zeolite [74]. Besides the framework titanium species identified by UV Raman spectroscopy excited at 244 nm, another titanium species with octahedral coordination (TiO 6 ) was confirmed by UV Raman spectroscopy with the excitation line at 266 nm (Fig.…”

“…Different from the peroxo species formed on Fe/ZSM-5 catalyst, the Fe 2 (l-O) 2 site with the Fig. 6 a Two kinds of titanium species characterized by UV resonance Raman spectroscopy; b In situ UV Raman cell for characterizing the propylene epoxidation reaction; c The proposed pathway during the propylene oxidation on the two kinds of active centers [74] featured Raman band at 730 cm -1 is formed on Fe/ZSM-35 catalyst upon N 2 O reacting with the Fe 2 (l-O) site (Fig. 7c) [61,102].…”

Switching off H2O2 Decomposition during TS-1 Catalysed Epoxidation via Post-Synthetic Active Site Modification

“…The 325 nm UV-Raman spectrum of TS-1 is presented in Figure 7c. In addition to the two vibrations related to the zeolite framework at 380 and 800 cm ) has previously been assigned to the symmetric stretching vibration of framework Ti-O-Si species [22,23]. Both the 960 and 1125 cm ), and a totally symmetric stretching mode, i.e., breathing mode, of the same unit (1125 cm −1 ), respectively [11].…”

In-situ 31P MAS NMR probing of the active centers in Ti silicalite molecular sieve

“…It has been found to catalyze many useful hydrocarbons with hydrogen peroxide under mild conditions [1][2][3][4][5][6]. During the past three decades, numerous research groups have been focusing on the synthesis, reaction performance, and especially the characterization of the active centers of TS-1 zeolite [7][8][9][10]. Different methods, such as XRD, Raman, power diffraction, solid state NMR and theoretical calculations, have been used to identify the catalytic active centers of TS-1 zeolite [10][11][12][13][14][15][16].…”