Evidences for charge-transfer complex formation in the benzene adsorption on sulfated TiO2-a resonance Raman spectroscopy investigation

Benzene adsorbed on highly acidic sulfated TiO2 (S-TiO2) shows an intriguing resonance Raman (RR) effect, with excitation in the blue-violet region. There are very interesting spectral features: the preferential enhancement of the e(2g) mode (1595 cm(-1)) in relation to the a(1g) mode (ring-breathing mode at 995 cm(-1)) and the appearance of bands at 1565 and 1514 cm(-1). The band at 1565 cm(-1) is probably one of the components of the e(2g) split band, originally a doubly degenerate mode (8a, 8b) in neat benzene, and the band at 1514 cm(-1) is assigned to the 19a mode, an inactive mode in neat benzene. These facts indicate a lowering of symmetry in adsorbed benzene, which may be caused by a strong interaction between S-TiO2 and the benzene molecule with formation of a benzene to Ti (IV) charge transfer (CT) complex or by the formation of a benzene radical cation species. However, the RR spectra of the adsorbed benzene cannot be assigned to the benzene radical cation because the observed wavenumber of the ring-breathing mode does not have the value expected for this species. Moreover, it was found by ESR measurements that the amount of radicals was very low, and so it was concluded that a CT complex is the species that originates the RR spectra. The most favorable intensification of the band at 1595 cm(-1) in the RR spectra of benzene/S-TiO2 at higher excitation energy corroborates this hypothesis, as an absorption band in this energy range, assigned to a CT transition, is observed. Copyright (C) 2008 John Wiley & Sons, Ltd.

Effect of the Y(2)O(3)-ZrO(2) support composition on nickel catalyst evaluated in dry reforming of methane

Nickel catalysts with a load of 5 wt.% Ni, supported on pure ZrO(2) and ZrO(2) stabilized with 4 mol%, 8 mol% and 12 mol% of Y(2)O(3), were prepared by the polymerization method. The samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction with hydrogen (TPR-H(2)), specific surface area (BET) and electronic paramagnetic resonance (EPR) and tested as catalysts for carbon dioxide reforming of methane. The XRD patterns showed the presence of the oxide precursor (NiO) and the tetragonal phase of a Y(2)O(3)-ZrO(2) solid solution. According to the TPR-H(2) analysis, the reduction of various NiO species was influenced by the composition of the support. Catalytic tests were conducted at 800 degrees C for 6 h, and the composition of the gaseous products and the catalytic conversion rate depended on the composition of the Y(2)O(3)-ZrO(2) solid solution and its influence on the supported NiO species. A direct relation was observed between the variation in the support, the nickel species supported on it and the performance in the catalytic tests. (C) 2008 Elsevier B.V. All rights reserved.

Reduction of NO by CO on Cu/ZrO(2)/Al(2)O(3) catalysts: Characterization and catalytic activities

ZrO(2), gamma-Al(2)O(3) and ZrO(2)/gamma-Al(2)O(3)-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H(2), Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO(2)/gamma-Al(2)O(3) matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO(2). Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO(2). (C) 2009 Published by Elsevier Ltd.

Carbon dioxide reforming of ethanol over Ni/Y(2)O(3)-ZrO(2) catalysts

Supported nickel catalysts of composition Ni/Y(2)O(3)-ZrO(2) were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y(2)O(3)-ZrO(2) in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO(2) conversion of 61% on the 5NiYZ catalyst at 800 degrees C, representing a better response than for the catalyst of the same composition prepared by wet impregnation. (C) 2009 Published by Elsevier B.V.