Authors:Karl D. Hammond; Wm. Curtis Conner Pages: 1 - 101 Abstract: Publication date: 2013 Source:Advances in Catalysis, Volume 56 Author(s): Karl D. Hammond, Wm. Curtis Conner Heterogeneous catalysis usually takes place by sequences of reactions involving fluid-phase reagents and the exposed layer of the solid catalyst surface. Estimation of the total catalyst surface area, its potential accessibility to gas- or liquid-phase reactants, and general catalytic activity are initially based on the morphology of the catalyst. Universally, measurements of adsorption and their interpretation are used to estimate the surface area and porosity relevant to catalytic reactions. We provide here a description of many traditional and recent techniques in adsorption-based catalyst characterization intended for experimental practitioners of adsorption. Our chapter includes descriptions of which regions of the isotherm correspond to micropore filling, mesopore filling, surface coverage, and saturation, supplemented by discussions of model isotherms, from the Langmuir isotherm and the Brunauer–Emmett–Teller theory to the Halsey equation. Pore size distribution methods include the Barrett–Joyner–Halenda and related methods for mesopores, empirical methods developed for micropores, and simulation-based methods that have finally resolved the differences between adsorption (increasing loading) and desorption (decreasing loading). This chapter also includes a discussion of hysteresis and metastability, both of which “trip up” experimentalists from time to time. We finish with a description of data acquisition methods and equipment, which are often obscured behind the facade of automation, and a discussion of what users should be aware of and what can go wrong.
Authors:Tracy J. Benson; Prashant R. Daggolu; Rafael A. Hernandez; Shetian Liu; Mark G. White Pages: 187 - 353 Abstract: Publication date: 2013 Source:Advances in Catalysis, Volume 56 Author(s): Tracy J. Benson, Prashant R. Daggolu, Rafael A. Hernandez, Shetian Liu, Mark G. White The composition of a typical pyrolysis oil is used to pose the problem of oxygen removal from this oil and to motivate a discussion of the different reactions for oxygen removal that are thermodynamically favored. From a consideration of this thermodynamics analysis of the favored reactions, the surface chemistry literature is surveyed to reveal those materials that allow the adsorption of oxygen-containing species. Included in this survey are experimental and theoretical studies. This consideration of adsorption of oxygen-containing species prompts a further examination of the literature of reaction mechanisms and reaction sequences to reveal the conventional pathways to remove oxygen from the substrates. Moreover, the literature of hydroprocessing is reviewed to show how traditional hydrodesulfurization catalysts have been studied as a hydrodeoxygenation (HDO) catalyst of the reactive species in pyrolysis oils. Furthermore, aqueous-phase reforming is discussed as an alternative to HDO.
Authors:Bjerne Clausen; James Dumesic Abstract: Publication date: 2013 Source:Advances in Catalysis, Volume 56 Author(s): Bjerne S. Clausen, James Dumesic
Authors:Robert Abstract: Publication date: 2013 Source:Advances in Catalysis, Volume 56 Author(s): Robert Schlögl This review is concerned with nanoscale carbon as a catalyst. Elemental carbon has become available in many nanostructured forms representing combinations of the hybridizations found in fundamental carbon allotropes, and the materials can be enriched by a large number of surface functional groups, some generated by nanostructuring. Consequently, many examples of catalytic applications of carbon are documented, but the development of the field has been hampered by the lack of a conceptual approach linking structure and function and by the lack of understanding of synthesis of the materials. This chapter provides a foundation for an advanced comprehension of the catalytic reactivity of carbon and addresses key aspects of characterization and synthesis. The usefulness of X-ray diffraction, Raman spectroscopy, and electron microscopy for the characterization of nanoscale carbons is briefly contrasted with the limitations of these methods. The various structural elements—among them carbon hybridization, local defects, and topology—that contribute to the electronic structure are discussed in detail. The difficulties of analyzing the resulting complex electron spectra are highlighted. In its core part, this chapter uses the derived knowledge of the electronic structure to arrive at concepts illustrating carbon’s potential in catalysis. A general synthesis strategy for the controlled functionalization of carbons is laid out. The ambivalent role of carbon deposits on catalyst surfaces as poisons or an active phase is demonstrated. One-third of the chapter is devoted to two case studies that illustrate the ideas; the catalytic transformations are the oxidative dehydrogenation of ethylbenzene and of alkanes.
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