Cássia Curan Turci

Oxidative dehydration of glycerol to acrylic acid over vanadium-impregnated zeolite beta

The oxidative dehydration of glycerol to acrylic acid was studied over vanadium-impregnated zeolite Beta. Catalysts were prepared by wet impregnation of ammonium metavanadate over ammonium-exchanged zeolite Beta, followed by air calcination at 823 K. Impregnation reduced the specific surface area, but did not significantly affected the acidity (Bronsted and Lewis) of the zeolites. The catalytic evaluation was carried out in a fixed bed flow reactor using air as the carrier and injecting glycerol by means of a syringe pump. Acrolein was the main product, with acetaldehyde and hydroxy-acetone (acetol) being also formed. Acrylic acid was formed with approximately 25% selectivity at 548 K over the impregnated zeolites. The result can be explained by XPS (X-ray photoelectron spectroscopy) measurements, which indicated a good dispersion of the vanadium inside the pores.

Generalized oscillator strengths for inner-shell excitation of SF6 recorded with a high-performance electron energy loss spectrometer

The generalized oscillator strength profiles for S 2p, S 2s and F 1s excited and ionized states of sulfur hexafluoride (SF6) are reported up to very high momentum transfer. These have been measured with a variable impact energy, variable scattering angle electron energy loss spectrometer, which is dedicated to studies of electric dipole (optically allowed) and non-dipole (optically forbidden electric quadrupole and spin-exchange) inner shell electronic transitions of gases, and systematic measurements of their angular and impact energy distributions in order to derive generalized oscillator strength profiles. In addition to presenting the SF6 results, we describe the design, construction and performance of the instrument, as well as data acquisition and analysis procedures. ” 2000 Published by Elsevier Science B.V. All rights reserved.

Generalized oscillator strengths for C 1s excitation of acetylene and ethylene

Abstract The generalized oscillator strength profiles for discrete C 1s excited states of C 2 H 2 and C 2 H 4 have been derived from angle-dependent inelastic electron scattering cross-sections measured with 1300 eV final electron energy. The measured GOS profiles for the strong C 1s→π* transition in each species are compared to theoretical calculations computed within the first Born approximation, using ab-initio generalized multi structural wave functions. These wave functions include relaxation, correlation and hole localization effects. Theory predicts large quadrupole contributions to the π* GOS of each species, analogous to those previously reported for computed GOS profiles for O 1s→π* excitation of CO 2 . We find good agreement between experiment and theory as to the shape of the π* GOS but, when the relative GOS extracted from the experimental data is normalized to the optical oscillator strength at K 2 =0, the magnitude is in better agreement with the GOS computed for only the dipole channel than for the sum of the dipole and quadrupole channels.

Electron impact core excitation of molecules: non-dipole spectroscopy and generalized oscillator strengths

Abstract A status report on the field of non-dipole core excitation electron energy loss spectroscopy is given together with a summary of recent studies of S2 s generalized oscillator strengths (GOS) of SF 6 and C1 s excitation in isomeric xylenes.

Generalized oscillator strength profiles for inner shell excitation of CO2 derived from variable angle electron energy loss spectroscopy

Abstract GOS profiles for C 1 s and O 1 s excitation of CO 2 have been derived from inner shell electron energy loss spectra of CO 2 measured over a wide range of scattering angles (4–62°). The experimental profiles are compared to computed GOS profiles calculated within the first Born approximation, using ab-initio configuration interaction wave functions for the C 1 s transitions and ab-initio generalized multi structural wave functions for the O 1 s transitions. The theoretical and experimental results are in generally good agreement indicating that the first Born approximation holds to a surprisingly large momentum transfer for the core excitations studied. The computations predict there should be oscillations in the GOS for O 1 s →ns σ g (536.5, 539 eV) and np σ u Rydberg states (∼539 eV) but not for π symmetry states. Measurements with a newly installed parallel detector provide experimental support for the existence of oscillations in the GOS profile for the O 1 s excitation of CO 2 at 539 eV. These oscillations may arise from interference between core excitations localized on the left or right oxygen atom of CO 2 .

Vibrational and electronic spectroscopy of neutral antimony coordination compounds of the 1,3-dithiole-2-thione-4,5-dithiolate (dmit).

The S 1s X-ray absorption near edge structure (XANES) and X-ray photoelectron spectra (XPS) of the neutral complexes [SbL(dmit)] (L = Br or I; dmit =1,3-dithiole-2-thione-4,5-dithiolate) have been measured using tunable synchrotron radiation. The valence shell electronic excitation by ultraviolet-visible (UV-vis) spectroscopy and the infrared vibrational spectra are presented and analyzed. The UV-vis results lead to an assignment of bands at 400 nm as π(Sm) → π*(C═S), where S(m) is the thiolate sulfur. The corresponding S 1s → π*(C═S) transition was identified at 2468.3 eV. Ab initio calculations, within the improved virtual orbital (IVO) method, carried out with the GSCF3 program, were applied to establish a complete and accurate spectral assignment. It has been the first attempt to apply such methodology for dmit coordination compounds, and very consistent results were obtained.

Visitas guiadas ao Museu Nacional: interações e impressões de estudantes da Educação Básica

This work involved the planning, implementation and evaluation of guided visits by public school students from the municipality of Rio de Janeiro to the National Museum of Federal Univer- sity of Rio de Janeiro (UFRJ). The theoretical background is the Contextual Model of Learning with its personal, physical and sociocultural contexts as facilitators of learning in museums. The main objective was to analyze the visits in relation to learning, motivation and affective gains. It was also aimed to establish the National Museum as a setting for the development of a non-formal school chemistry class. Questionnaires were administered before, during and after visits. The results showed that the procedure and dynamic developed were able to provide cognitive and affective gains for the students. The physical context of the National Museum promotes the development of non-formal classes in Chemistry, especially for high school students.