Oxidations carried out by means of vanadium oxide catalysts
TL;DR: In this paper, it was shown that the partial pressures of the reacting substances appeared to influence the reaction rate, and a formula depicting this influence was derived, which may be interpreted by assuming two successive reactions, namely the reaction between the aromatic and the oxygen on the surface, and the re-oxidation of the partly reduced surface by means of oxygen.
About: This article is published in Chemical Engineering Science.The article was published on 1954-01-01. It has received 1613 citations till now. The article focuses on the topics: Vanadium oxide & Catalysis.
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TL;DR: It is considered more feasible that the rate-deter-mining step is the cleavage of the C-H bond at the R-carbon atom, and the active site consists of an ensemble of metallic Auatoms and a cationic Au.
Abstract: ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au
1,784 citations
TL;DR: In this article, structural and electronic properties and energetic quantities related to the formation of oxygen defects at transition metal (TM) and rare earth (RE) oxide surfaces, neutral oxygen vacancies in particular, play a major role in a variety of technological applications.
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TL;DR: This tutorial review focuses on the recent progress in disclosing the factors that affect the activity of reactive sites, including characterization of atomic coordination number, structural defects and disorder in ultrathin two-dimensional sheets by X-ray absorption fine structure spectroscopy, positron annihilation spectroscopic, electron spin resonance and high resolution transmission electron microscopy.
Abstract: Catalysis can speed up chemical reactions and it usually occurs on the low coordinated steps, edges, terraces, kinks and corner atoms that are often called “active sites”. However, the atomic level interplay between active sites and catalytic activity is still an open question, owing to the large difference between idealized models and real catalysts. This stimulates us to pursue a suitable material model for studying the active sites–catalytic activity relationship, in which the atomically-thin two-dimensional sheets could serve as an ideal model, owing to their relatively simple type of active site and the ultrahigh fraction of active sites that are comparable to the overall atoms. In this tutorial review, we focus on the recent progress in disclosing the factors that affect the activity of reactive sites, including characterization of atomic coordination number, structural defects and disorder in ultrathin two-dimensional sheets by X-ray absorption fine structure spectroscopy, positron annihilation spectroscopy, electron spin resonance and high resolution transmission electron microscopy. Also, we overview their applications in CO catalytic oxidation, photocatalytic water splitting, electrocatalytic oxygen and hydrogen evolution reactions, and hence highlight the atomic level interplay among coordination number, structural defects/disorder, active sites and catalytic activity in the two-dimensional sheets with atomic thickness. Finally, we also present the major challenges and opportunities regarding the role of active sites in catalysis. We believe that this review provides critical insights for understanding the catalysis and hence helps to develop new catalysts with high catalytic activity.
803 citations
TL;DR: The results provide atomic-scale verification of a general mechanism originally proposed by Mars and van Krevelen in 1954 and are likely to be of general relevance for the mechanism of catalytic reactions at oxide surfaces.
Abstract: The structure of RuO(2)(110) and the mechanism for catalytic carbon monoxide oxidation on this surface were studied by low-energy electron diffraction, scanning tunneling microscopy, and density-functional calculations. The RuO(2)(110) surface exposes bridging oxygen atoms and ruthenium atoms not capped by oxygen. The latter act as coordinatively unsaturated sites-a hypothesis introduced long ago to account for the catalytic activity of oxide surfaces-onto which carbon monoxide can chemisorb and from where it can react with neighboring lattice-oxygen to carbon dioxide. Under steady-state conditions, the consumed lattice-oxygen is continuously restored by oxygen uptake from the gas phase. The results provide atomic-scale verification of a general mechanism originally proposed by Mars and van Krevelen in 1954 and are likely to be of general relevance for the mechanism of catalytic reactions at oxide surfaces.
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TL;DR: In this article, the crystal structure of V2O5 was analyzed in relation to the well-known tendency of vanadium pentoxide in colloidal solution to form rod-like particles.
Abstract: THE analysis of the crystal structure of V2O5 seemed to be of special interest in relation to the well-known tendency of vanadium pentoxide in colloidal solution to form rod-like particles. Further, practically nothing is known about the structure of compounds of the form A2B5, such as Nb2O5 and Ta2O5, as well as V2O5.
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TL;DR: In this paper, the authors investigated the kinetics of the oxidation of sulphur dioxide with oxygen using a commercial vanadium pentoxide catalyst and found that the rate-determining step is the reaction between gaseous oxygen and chemisorbed sulfur dioxide.
Abstract: The kinetics of the oxidation of sulphur dioxide with oxygen using a commercial vanadium pentoxide catalyst has been investigated. Experimental conditions have been chosen such that the reaction has been carried out isothermally in a flow-type reactor at temperatures (360° to 450°) and conversions (up to 10%) where the reverse reaction may be ignored.
The results, analysed in conjunction with the relevant adsorption isotherms and rates of adsorption on the clean catalyst, indicate that the rate-determining step is the rate of reaction between gaseous oxygen and chemisorbed sulphur dioxide.
The adsorption isotherms, which are Langmuir in character, indicate the presence of at least two different types of active centres. Both oxygen and sulphur dioxide are reversibly chemisorbed, oxygen being weakly bound with a heat of adsorption of 6·4 kcal. and sulphur dioxide strongly bound with a heat of 28·8 kcal. There is evidence that both adsorbed species possess considerable mobility on the surface.
Measurements of the rates of adsorption of SO2 and O2 on the clean surface indicate that oxygen is adsorbed by a second-order mechanism at a slower rate than the observed rate of reaction, whereas sulphur dioxide is adsorbed by a third-order mechanism at a much faster rate than the rate of reaction. Adsorption equilibrium of SO2 may be assumed, under the conditions of reaction, without sensible error.
Adsorption-rate measurements of both SO2 and O2 indicate that the number of active centres (defects) increases with temperature, according to a relationship of the type d ln L/dT = A/RT2 where L = no. of active centres, as suggested by Volkenstein (1949).
With SO2, reaction between it and an active centre requires no activation energy, the increase in rate with increase in temperature being due entirely to the increase in the number of active centres. With O2, a small activation energy may be required, although the main increase in rate of adsorption with temperature is similarly due to the increase in the number of active centres with temperature.
Some interesting comparisons are made between the results of these adsorption measurements and recent work on the semi-conductivity of oxide catalysts, notably by Bevan & Anderson (1950) and Garner, Gray & Stone (1950). Several points of similarity are noted which indicate lines for further work.
Finally, a mechanism for the catalytic oxidation of sulphur dioxide is proposed, the main features of which are:
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