Meiling Guo

In situ UV Raman spectroscopic study on the synthesis mechanism of AlPO-5.

Despite these efforts, a thorough understandingof the template effect, particularly the significance of the roleof templating in the channel formation of aluminophosphatemolecular sieves, is still lacking because of the complexity ofthe synthesis process.Avery powerful but relatively unexplored way of probingthis process is to perform in situ characterization underworking conditions.

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

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.

Note: Deep ultraviolet Raman spectrograph with the laser excitation line down to 177.3 nm and its application

Deep UV Raman spectrograph with the laser excitation line down to 177.3 nm was developed in this laboratory. An ellipsoidal mirror and a dispersed-subtractive triple monochromator were used to collect and disperse Raman light, respectively. The triple monochromator was arranged in a triangular configuration with only six mirrors used. 177.3 nm laser excited Raman spectrum with cut-off wavenumber down to 200 cm(-1) and spectral resolution of 8.0 cm(-1) can be obtained under the condition of high purity N2 purging. With the C-C σ bond in Teflon selectively excited by the 177.3 nm laser, resonance Raman spectrum of Teflon with good quality was recorded on the home-built instrument and the σ-σ(*) transition of C-C bond was studied. The result demonstrates that deep UV Raman spectrograph is powerful for studying the systems with electronic transition located in the deep UV region.

Synthesis and Morphology Control of AM-6 Nanofibers with Tailored -V-O-V- Intermediates

Microporous vanadosilicates with octahedral VO6 and tetrahedral SiO4 units, better known as AM-6, have been hydrothermally synthesized with different morphologies by controlling the Na/K molar ratio of the initial gel mixtures. The morphology of the AM-6 materials changed from bulky cube to nanofiber aggregates as the Na/K molar ratio decreased from 1.9 to 0.2. Raman spectroscopy revealed that the VO3 (-) intermediate species plays an important role in the formation of the nanofiber morphology. The orientation of -V-O-V- chains in nanofiber aggregates was examined by confocal polarized micro-Raman spectroscopy. It was found that these aggregates are assemblies of short -V-O-V- chains perpendicular to the axis of nanofibers. The obtained AM-6 nanofibers greatly increase the exposed proportion of VO terminals, and thus improve the catalytic performance.

UV Raman Spectroscopic Studies on the Synthesis Mechanism of FeAlPO4-5

Abstract FeAlPO4-5 samples with various iron contents were investigated by UV resonance Raman spectroscopy and UV-Vis spectroscopy. The Raman spectra of FeAlPO4-5 show four feature bands related to the framework iron at 630, 1060, 1140, and 1210 cm−1 when excited by 266 nm laser. It is found that only part of ferric ions could enter into the framework, while the others exist in the extra-framework in the form of six-coordinated state. This kind of iron gives characteristic Raman band at 285 cm−1. Combined with UV resonance Raman spectroscopy, UV-Vis spectroscopy, and X-ray diffraction, the crystallization process of FeAlPO4-5 (Al/Fe = 760) was studied. It is found that, in the early stages of the crystallization, the iron species exist in the form of six-coordinated state while attached to the end of the 1-dimensional AlPO4 chain. The Fe–O bonds in the six-coordinated state hamper the crystallization of AlPO4. The crystallization of the FeAlPO4-5 began when the reaction between the 1-dimensional AlPO4 chains occurred. At the same time, the six-coordinated ferric ions converted to the tetrahedral iron.