1,721,021 research outputs found
Use of overtone bands to monitor the state of the catalyst active phases during infrared studies of adsorption and catalytic reactions
No full textOvertone bands are observable in the i.r. spectra of mixed and supported oxide catalysts, and may be informative on the state of the active phases and their interactions with absorbates. In the cases of supported V2O5/TiO2, MoO3/Al2O3 and WO3/Al2O3 the behaviour of such bands indicates that single uncoupled MO bonds are exposed on the surface. In the case of bulk VPO catalysts they are informative on the presence of oxidized phases. © 1986
Fourier transform I.R. evidence of the formation of dioxymethylene species from formaldehyde adsorption on anatase and thoria
No full textHCHO adsorption on activated thoria produces, at 240 K, a species characterized as dioxymethylene; by heating at room temperature, it leads to formate and methoxy groups: the three species are observed by adsorption of HCHO on anatase at room temperature
FT-IR study of the effect of pretreatment on the surface properties of alumina produced by flame hydrolysis of aluminium trichloride
No full textA comparison of the behaviour of two samples of alumina obtained by pyrolysis of AlCl3 or thermal dehydration of boehmite has shown that the former contains chloride impurities that modify the spectra in the ν(OH) region as well as poison the strongest Lewis acid sites. The reactivity towards CO2, producing bicarbonates species, is also affected. Heat treatment in the presence of water partially eliminates Cl- and leads to a surface quite similar to that of the sample prepared by thermal dehydration of boehmite. © 1986
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
FT-IR characterization of the surface acidity of different titanium dioxide anatase preparations
No full textThe surface acidity of four different anatase preparations has been studied by FT-IR spectroscopy of adsorbed benzene, ammonia, pyridine, carbon monoxide and dioxide. Our results indicate that surface chemistry of anatase, in particular acidity, greatly depends on the preparation of the sample, both through the resulting morphology and the presence of surface impurities. Different morphologies may result in different types of Lewis acid sites. If pure, anatase does not show Brønsted acidity. The presence of silica impurities is responsible for an enhancement of Brønsted acidity on several samples, and may be evaluated by the intensity of an IR band situated near 3730 cm-1. Very strong Brønsted acidity is generated by the presence of sulfate impurities. © 1985
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Microcalorimetric and Fourier transform infrared spectroscopic studies of methanol adsorption on Al2O3
No full textAdsorption microcalorimetry and infrared measurements using CH3OH, CD3OH, and CHD2OH show the existence of at least three steps during the adsorption of methanol on alumina activated at 773 K. At very low coverages, molecules coordinated on the strongest Lewis sites are evident, which easily transform into bridged methoxide species. With increasing coverage, another form, irreversibly adsorbed at room temperature but desorbed by evacuation at 373-473 K, becomes predominant. It is identified as undissociated methanol strongly hydrogen bonded on a cation-anion couple having a strong basic character. Finally, at high coverages a reversible form hydrogen bonded to basic sites is detected. © 1985 American Chemical Society
- …
