1,721,053 research outputs found
Hydrogen Bonding Network Disruption in Mesoporous Catalyst Supports Probed by PFG-NMR Diffusometry and NMR Relaxometry
No full textThe pulsed-field gradient (PFG)-NMR technique has been applied to study molecular diffusion of organic liquids within mesoporous materials used in heterogeneous catalysis, in order to assess the effect of chemical functionalities on the effective self-diffusivity of the probe molecule within the pore space. True tortuosity values of the porous matrix can be calculated from the ratio of the unrestricted free self-diffusivity to the self-diffusivity within the pore space only when the small liquid-phase probe molecules do not have any chemical functionality that interacts within the solid phase (e.g., alkanes). The use of molecules with reactive chemical functionalities gives values heavily dependent on the physical and chemical interactions within the porous medium; hence, these values cannot be defined as tortuosity. Polyols showed an interesting behavior of enhanced rate of self-diffusion within the confined pore space, and this is attributed to the ability of the porous medium to disrupt the extensive intermolecular hydrogen bonding network of polyols
In-situ 13C DEPT NMR spectroscopic studies of aerobic oxidation of benzyl alcohol over heterogeneous Pd/Al2O3 catalyst
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Nuclear magnetic resonance relaxometry in heterogeneous catalysis: New advances in understanding adsorption over solid catalyst surfaces
No full textCharacterizing the influence of liquid-surface interactions on molecular diffusion in catalysts
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Handbook of Green Chemistry Series
No full textNMR Spectroscopy and Microscopy in Reaction Engineering and Catalysi
Interpretation of NMR Relaxation as a Tool for Characterising the Adsorption Strength of Liquids inside Porous Materials
No full textNuclear magnetic resonance (NMR) relaxation times are shown to provide a unique probe of adsorbate–adsorbent interactions in liquid-saturated porous materials. A short theoretical analysis is presented, which shows that the ratio of the longitudinal to transverse relaxation times (T1/T2) is related to an adsorbate–adsorbent interaction energy, and we introduce a quantitative metric esurf (based on the relaxation time ratio) characterising the strength of this surface interaction. We then consider the interaction of water with a range of oxide surfaces (TiO2 anatase, TiO2 rutile, γ-Al2O3, SiO2, θ-Al2O3 and ZrO2) and show that esurf correlates with the strongest adsorption sites present, as determined by temperature programmed desorption (TPD). Thus we demonstrate that NMR relaxation measurements have a direct physical interpretation in terms of the characterisation of activation energy of desorption from the surface. Further, for a series of chemically similar solid materials, in this case a range of oxide materials, for which at least two calibration values are obtainable by TPD, the esurf parameter yields a direct estimate of the maximum activation energy of desorption from the surface. The results suggest that T1/T2 measurements may become a useful addition to the methods available to characterise liquid-phase adsorption in porous materials. The particular motivation for this work is to characterise adsorbate–surface interactions in liquid-phase catalysis
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
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
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