The active sites in different TS-1 zeolites for propylene epoxidation studied by ultraviolet resonance Raman and ultraviolet visible absorption spectroscopies

The titanium species in four kinds of titanium-containing MFI zeolites have been studied by ultraviolet (UV)-Raman and ultraviolet visible (UV-Vis) absorption spectroscopies and by the epoxidation of propylene with diluted H2O2 solution (30%). UV-Raman spectroscopy is proved to be a suitable means to estimate qualitatively the framework titanium in TS-l zeolites. Based on the comparison of the relative intensity ratio I-1125/I-380 of UV-Raman spectra, the TS-1(conv.) sample synthesized hydrothermally by the conventional procedure shows the highest amount of framework titanium. UV-Vis spectroscopy reveals that besides minor anatase. titanium species are mainly tetrahydrally coordinated into the framework for TS-l(conv.) or the Ti-ZSM-5 sample prepared by gas-solid reaction between deboronated B-ZSM-5 and TiCl4 vapor at elevated temperatures. For the TS-1(org.) and TS-1(inorg.) samples synthesized hydrothermally using tetrapropylammonium bromide (TPABr) as template and tetrabutylorthotitanite (TBOT) and TiCl3 as titanium source, respectively, the presence of mononuclear and isolated TiOx species which are proposed to bond to the zeolite extraframework is observed. In addition to the framework titanium species, these isolated TiOx species are assumed to be also active for propylene epoxidation.

Direct spectroscopic evidence for vanadium species in V-MCM-41 molecular sieve characterized by UV resonance Raman spectroscopy

Vanadium species in tetrahedral and octahedral coordination in V-MCM-41 molecular sieve are characterized by UV resonance Raman bands at 1070 and 930 cm(-1) respectively.

Characteristic infrared spectroscopic patterns in the protein bands of human breast cancer tissue

Infrared (IR) spectra of normal, hyperplasia, fibroadenoma and carcinoma tissues of human breast obtained from 96 patients have been determined and analyzed statistically. Several spectral differences were detected in the frequency regions of N-H stretching, amide I, II and III bands: (1) the bands in the region 3000-3600cm-1 shifted to lower frequencies for the carcinomatous tissue; (2) the A(3300)/A(3075) absorbance ratio was significantly higher for the fibroadenoma than for the other types of tissues; (3) the frequency of the a-helix amide I band decreased for the malignant tissue, while the corresponding beta -sheet amide I band frequency increased; (4) the A(1657)/A(1635) and A(1553)/A(1540) absorbance ratios were the highest for fibroadenoma and carcinoma tissues; (5) the A(1680)/A(1657) absorbance ratio decreased significantly in the order of normal > hyperplasia > fibroadenoma > carcinoma; (6) the A(1651)/A(1545) absorbance ratio increased slightly for the fibroadenoma and the carcinoma tissues; (7) the bands at 1204 and 1278 cm(-1), assigned to the vibrational modes of the collagen, did not appear in the original spectra as resolved peaks and were distinctly stronger in the deconvoluted spectra of the carcinoma tissue and (8) the A(1657)/A(1204) and A(1657)/A(1278) absorbance ratios, both yielding information on the relative content of collagen, increased in the order of normal < hyperplasia < carcinoma < fibroadenoma. The said differences imply that the information is useful for the diagnosis of breast cancer and malignant breast abnormalities, and may serve as a basis for further studies on conformational changes in tissue proteins during carcinogenesis. (C) 2001 Elsevier Science B.V. All rights reserved.

UV Raman spectroscopic study on the synthesis mechanism of zeolite X

The synthesis of zeolite X is characterized by UV Raman spectroscopy, NMR spectroscopy, and X-ray diffraction. UV Raman spectra of the liquid phase of the synthesis system indicate that AI(OH); species are incorporated into silicate species, and the polymeric silicate species are depolymerized into monomeric silicate species during the early stage of zeolite formation. An. intermediate species possessing Raman bands at 307, 503, 858 and 1020 cm(-1) is detected during the crystallization ill the solid phase transformation. The intermediate species is attributed to the beta cage, the secondary building unit of zeolite X. A model for the formation of zeolite X is proposed, which involves four-membered rings connecting to each other via six-membered ring to form beta cages, then the beta cages interconnect via double six-membered rings to form the framework of zeolite X. (C) 2001 Elsevier Science B.V. All rights reserved.

Comparative X-ray photoelectron spectroscopic study on the desulfurization of thiophene by Raney Nickel and rapidly quenched skeletal nickel

The desulfurization of thiophene on Raney Ni and rapidly quenched skeletal Ni (RQ Ni) has been studied in ultrahigh vacuum (UHV) by X-ray photoelectron spectroscopy (XPS). The Raney Ni or RQ Ni can be approximated as a hydrogen-preadsorbed polycrystalline Ni-alumina composite. It is found that thiophene molecularly adsorbs on Raney Ni or RQ Ni at 103 K. At 173 K, thiophene on alumina is desorbed, while thiophene in direct contact with the metallic Ni in Raney Ni undergoes C-S bond scission, leading to carbonaceous species most probably in the metallocycle-like configuration and atomic sulfur. On RQ Ni, the temperature for thiophene dissociation is about 100 K higher than that on Raney Ni. The lower reactivity of RQ Ni toward thiophene is tentatively attributed to lattice expansion of Ni crystallites in RQ Ni due to rapid quenching. The existence of alumina and hydrogen may block the further cracking of the metallocycle-like species on Raney Ni and RQ Ni at higher temperatures, which has been the dominant reaction pathway on Ni single crystals. By 473 K, the C Is peak has disappeared, leaving nickel sulfide on the surface.