87,341 research outputs found
Correction: Optical bands of dodecanuclear compounds H<sub>4</sub>PVMo<sub>11</sub>O<sub>40</sub>∙yH<sub>2</sub>O with Keggin structure. Semiclassical vibronic model
No full textCorrection for ‘Optical bands of dodecanuclear compounds H4PVMo11O40∙yH2O with Keggin structure. Semiclassical vibronic model’ by S. Klokishner et al., Phys. Chem. Chem. Phys., 2004, 6, 2066–2082, https://doi.org/10.1039/B312753B. The authors apologise that the name of co-author F. C. Jentoft was misspelled on the original manuscript. The correct name is shown in the affiliation above. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers
In Situ Vibrational Spectroscopy of Reactants and Probe Molecules on Oxide Catalysts
No full textVibrational spectroscopy is not a priori a surface-sensitive method but it becomes surface-sensitive when either functional groups present on the surface are analyzed or when observing an adsorbed probe or reactant. In this respect, it is a unique tool that often allows identifying changes of the catalyst itself upon adsorbing a molecule and the nature of the adsorbed species. Moreover, it can be applied in situ, i.e. while a catalytic reaction is in progress, and changes of surface functionalities and adsorbates can be monitored and correlated to catalytic performance. The accessible temperature and pressure ranges are wide, from liquid helium temperature to several hundred degrees Celsius and from the sub-Pa range to MPa. The possibilities of IR spectroscopy in investigating powder catalysts will be illustrated using two examples: 1) Reactive probe molecule spectroscopy on silica-supported silver catalysts Silica-supported silver catalysts are suitable for the hydrogenation of ,-unsaturated aldehydes to the respective alcohols [1]. In order to elucidate the mechanism of H2 activation the interaction of H2 with pure silica and an 8 at% Ag-containing catalyst were studied. Interaction of H2 (or D2) with the hydroxyl groups of the silica support was observed at 77 K. At 100 mbar D2 and room temperature or above, exchange of OH- to OD-groups occurred. The exchange reaction requires cleavage of the hydrogen molecule and can thus be taken as a model reaction for hydrogen activation. The kinetics of the exchange reaction was studied spectroscopically. 2) In situ DRIFTS investigations of n-butane isomerization catalyzed by sulfated zirconia With the diffuse reflectance method, spectra can be obtained of powder beds, which are more suitable for catalytic reactions than wafers, and possible changes to the sample through pressingas have been found for sulfated zirconia [2]can be avoided. Spectra taken of sulfated zirconia catalysts during isomerization at temperatures of 323 to 378 K and 1 kPa n-butane partial pressure are highly complex since they exhibit intense gas phase absorptions, alterations to the sulfate bands, and bands that possibly indicate the formation of water. Series of spectra were analyzed for simultaneous changes of various features, and correlations between spectral developments and the catalytic performance will be discussed. [1] P. Claus, H. Hofmeister, J. Phys. Chem. B 103 (1999) 2766-2775; P. Claus, P.A. Crozier, P. Druska, Fresenius J. Anal. Chem. 361 (1998) 677-679. [2] B.S. Klose, R.E. Jentoft, A. Hahn, T. Ressler, J. Kröhnert, S. Wrabetz, X. Yang, F.C. Jentoft, J. Catal. 217 (2003) 487-490
Structural, Surface, and Catalytic Properties of Aluminas
No full textThe published data concerning the structural, surface, and catalytic properties of aluminas are reviewed, and these properties are related to the preparation procedures.
The experimental and computational investigations of the structural characteristics of the polymorphs most useful for applications in catalysis, which are γ-, η-, δ-, and θ-Al2O3, are critically analyzed. The thermodynamics of the various polymorphs and the kinetics of the phase transitions are considered. The available information on Brønsted sites (i.e., hydroxyl groups), Lewis acid sites, and acid–base pairs othe surface of aluminas is discussed. Data regarding the application of aluminas as a catalyst and as a catalyst support are summarized. Suggestions for future research are
proposed
Variations on the Author
No full text“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
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
In Situ Diffuse Reflectance IR Spectroscopic Investigation of n-Butane Isomerization on Promoted Sulfated Zirconia Catalysts
No full textIntroduction
Sulfated zirconia (SZ) is an attractive catalyst for low temperature butane isomerization [1]. Its activity can be improved by 1–2 orders of magnitude through addition of promoters such as iron or manganese in cationic form [2,3]. The state of these promoters has been characterized, and depending on the method of preparation, a major fraction is found to form a solid solution with zirconia [4]. It has been proposed that promoters facilitate reaction initiation via oxidative dehydrogenation to butenes, which may be converted into the reaction carriers, viz. carbenium ions. Only indirect evidence such as better activity after activation in oxidizing than in inert atmosphere has been presented [5]. Reaction profiles recorded under moderate reaction conditions (e.g. 323 K, 1 kPa n-butane) show an induction period and zero conversion in the extrapolation to zero time on stream. Either the catalyst becomes active only in the feed, or intermediates accumulate on the surface. We have focused on manganese as a promoter and have used in situ diffuse reflectance IR spectroscopy (DRIFTS) to reveal the effects of activation or regeneration in inert gas or O2, and to monitor the events during the induction period.
References
1. Hino, M., Arata, K., J. Am. Chem. Soc. 101, 6439 (1979).
2. Hsu, C.-Y., Heimbuch, C.R., Armes, C.T., Gates, B.C., Chem. Commun. 1645 (1992).
3. Lange, F.C., Cheung, T.-K., Gates, B.C., Catal. Lett. 41, 95 (1996).
4. Jentoft, F.C., Hahn, A., Kröhnert, J., Lorenz, G., Jentoft, R.E., Ressler, T., Wild, U., Schlögl, R., J. Catal. 224, 124 (2004).
5. Wan, K.T., Khouw, C.B., Davis, M.E., J. Catal. 158, 311 (1996)
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
Reactivity of Nanocrystalline Sulfated Zirconia Thin Films
No full textIntroduction
Sulfated zirconia (SZ) has been found to be catalytically active for the isomerization of n-butane at room temperature [1]. This discovery has led to numerous investigations into the catalyst; however, no consistent theories have been devised to satisfactorily describe the nature of the active sites [2]. In order to improve surface characterization, a model system consisting of a nanocrystalline SZ thin film supported on a silicon wafer has previously been developed [3]. The present work addresses two issues: the role of the atmosphere during thermal treatment and the validation of the model through demonstration of its reactivity towards n-butane.
[1] M. Hino, K. Arata., J. Am. Chem. Soc. 101 (1979) 6439.
[2] X. Song and A. Sayari, Catal. Rev. - Sci. Eng. 38 (1996) 329.
[3] F.C. Jentoft, A. Fischer, G. Weinberg, U. Wild, R. Schlögl, Stud. Surf. Sci. Cat. 130 (2000) 209
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
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