N-ethyl Formamide Dehydration Research Articles

ChemInform Abstract: Catalytic Cooperation Between MoO3 and Sb2O4 in N-Ethyl Formamide Dehydration. Part 3. Comparison of a Mathematical Model Based on the Remote Control Mechanism with Experimental Results.

ChemInform Abstract: Catalytic Cooperation Between MoO3 and Sb2O4 in N-Ethyl Formamide Dehydration. Part 3. Comparison of a Mathematical Model Based on the Remote Control Mechanism with Experimental Results.

ChemInform Abstract: Catalytic Cooperation Between MoO3 and Sb2O4 in N-Ethyl Formamide Dehydration. Part 2. Nature of Active Sites and Role of Spillover Oxygen.

ChemInform Abstract: Catalytic Cooperation Between MoO3 and Sb2O4 in N-Ethyl Formamide Dehydration. Part 2. Nature of Active Sites and Role of Spillover Oxygen.

ChemInform Abstract: Catalytic Cooperation Between MoO3 and Sb2O4 in N‐Ethyl Formamide Dehydration. Part 1. Preparation, Characterization, and Catalytic Results.

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Catalytic cooperation between MoO 3 and Sb 2O 4 in N-ethyl formamide dehydration I. Preparation, characterization, and catalytic results

Catalysts containing MoO 3 and α-Sb 2O 4 with different “architectures” were prepared by different methods: mixing of separately prepared pure oxides, impregnation of MoO 3 by Sb 2O 4 or vice versa. We report results obtained in the oxygen-aided dehydration of N-ethyl formamide catalyzed by these solids. A strong synergy between Mo and Sb is always observed. Extensive characterization of the catalysts before and after catalytic test, by X-ray diffraction, Electron Microscopy, Analytical Electron Microscope, XPS, and Ion Scattering Spectroscopy excludes the formation of mixed oxides or solid solutions as well as mutual contamination. Rather, the artificial contamination created by impregnation with a precursor of the other oxide exhibits a strong tendency to disappear. The catalytic synergy persists after the contamination has disappeared. The origin of the observed synergy is attributed to a remote control mechanism, namely spillover oxygen produced by α-Sb 2O 4 creates and/or regenerates active and selective sites on MoO 3.

Catalytic cooperation between MoO 3 and Sb 2O 4 in N-ethyl formamide dehydration II. Nature of active sites and role of spillover oxygen

The present work reports experiments designed to further investigate the role of MoO 3 and Sb 2O 4 in the cooperative effect they exhibit in N-ethyl formamide dehydration. Temperature-programmed desorption of NH 3 showed that Bronsted acid sites are responsible for activity. TPD of CO 2 gave no indication of basic sites. The Brønsted sites are sensitive to reduction and reoxidation. Thermoreoxidation of previously reduced molybdenum oxide and oxidation of carbon deposited on MoO 3 are more rapid when α-Sb 2O 4 is admixed. The interpretation of the phenomenon is that α-Sb 2O 4 dissociates molecular O 2 to an oxygen spillover species which can maintain MoO 3 at a high degree of oxidation and, if necessary, reoxidize it or remove deposited carbon. Brønsted sites necessitate a high degree of oxidation and their number is consequently promoted by spillover oxygen. Mechanisms are proposed for the dissociation of oxygen, the reoxidation of pre-reduced MoO 3, and the formation of Brønsted acid sites. The importance of the reported results for selective oxidation or multicomponent catalysts is discussed.

Catalytic cooperation between MoO 3 and Sb 2O 4 in N-ethyl formamide dehydration III. Comparison of a mathematical model based on the remote control mechanism with experimental results

We present a mathematical model of the remote control effect in the cooperation between α-Sb 2O 4 (spillover oxygen donor) and MoO 3 (acceptor and catalytic phase) in the oxygen assisted dehydration of formamides. The model is compared with experimental results obtained with 21 mechanical mixtures of α-Sb 2O 4 and MoO 3 of different compositions, at 3 different reaction temperatures, and oxygen partial pressure varying over a range of more than 2 orders of magnitude. The observed increase of activity of MoO 3 due to the effect of the remote control corresponds extremely well (variance of squared residue better than 3 × 10 −3) to the results of the mathematical model. We have verified that the magnitude of the kinetic parameters and surface concentration of spillover oxygen is physically acceptable, and that the variations of these parameters with the temperature correspond to those predicted by the general laws of physical chemistry.

Studies on the V2O5–TiO2system. Part 2.—TiO2(anatase)–V2O5

Mechanical mixtures of separately prepared V2O5, V6O13 and anatase have been used as catalysts in the dehydration of N-ethylformamide (NEF) in the presence of oxygen. Catalytic activity was measured as a function of the gas hourly space velocity (GHSV), the oxygen-to-N-ethylformamide ratio (O/N), the temperature, the V2O5 and V6O13 contents and the surface area of V2O5. The characterization was carried out using B.E.T. surface analysis, XRD and XPS techniques.It was concluded that there exists a cooperation between V2O5 and anatase, which brings about the stabilization of V6O13 by the anatase. V6O13 is the most selective phase in NEF dehydration. The calcination of V2O5–anatase mechanical mixtures results in (i) an increase of the V2O5 dispersion over the anatase surface, which brings about an increase of the selective product (propiononitrile), and (ii) partial anatase-into-rutile transformation, resulting in a decay of the catalytic properties. Under appropriate reaction conditions (temperature, O/N ratio) the anatase-into-rutile transformation does not take place.

Studies on the V2O5–TiO2system. Part 1.—TiO2(rutile)–V2O5

Mechanical mixtures of separately prepared V2O5 and TiO2(rutile) have been used as catalysts in the dehydration of N-ethylformamide (NEF) in the presence of oxygen. Catalytic activity has been measured as a function of the gas hourly space velocity (GHSV), the molar ratio of oxygen to NEF (O/N) and the composition of the catalysts. The characterization of fresh and used catalysts has been carried out using different physicochemical techniques: B.E.T. surface area analysis, XRD, XPS. It has been established that there exists a synergetic effect between rutile and V2O5 thus explaining the catalytic properties of their mechanical mixtures. V2O5 is dispersed over the surface of rutile grains in the course of the catalytic reaction. A simultaneous process of reduction and reoxidation of V2O5 takes place. The type of reduced vanadium oxide formed depends on the O/N ratio and GHSV. The deeply reduced and fully oxidized vanadium oxides are very active but are not selective. Medium reduced vanadium oxides are less active but give higher propiononitrile yields (the selective product). It was concluded that rutile disadvantages the stabilization of vanadium in a high oxidation state. It shifts the redox steady-state equilibrium of the vanadium phase towards the more reduced vanadium oxides.

Synergy in N-ethylformamide dehydration by mixtures of molybdenum trioxide and antimony oxide (.alpha.-Sb2O4)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynergy in N-ethylformamide dehydration by mixtures of molybdenum trioxide and antimony oxide (.alpha.-Sb2O4)B. Zhou, S. Ceckiewicz, and B. DelmonCite this: J. Phys. Chem. 1987, 91, 19, 5061–5067Publication Date (Print):September 10, 1987Publication History Published online1 May 2002Published inissue 10 September 1987https://doi.org/10.1021/j100303a036RIGHTS & PERMISSIONSArticle Views124Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (949 KB) Get e-Alerts

Two-phase catalysts in selective oxidation and related reactions

Catalytic properties of mechanical oxide mixtures : Sb 2O 4 + MoO 3 and TiO 2 + V 2 O 5 have been studied in two reactions : N-ethyl formamide dehydration and isobutylene oxidation. An interpretation of the results obtained is proposed on the basis of the remote control concept and an hypothesis about the junction between two cooperating phases.

Catalytic synergy between MoO 3 and BiPO 4 in N-ethyl formamide dehydration : III. An ESR study of reduction properties of the mixtures of MoO 3 and BiPO 4

A study of the interactions between MoO 3 and BiPO 4 in mixed oxide catalysts active in N-ethyl formamide dehydration was made by determining the Mo(V) Electron Spin Resonance (ESR) signal intensities after reduction, under different conditions, of mechanical mixtures of separately prepared BiPO 4 and MoO 3. The signal intensity clearly depended on the intimacy of contact, the reducibility of MoO 3 in mechanical mixtures being higher than in pure MoO 3. The mixing method in which both powders were dispersed together in n-pentane was the most effective. Alternate reducing and oxidizing treatments showed that the reaction was reversible at high temperature. After comparison of the ESR results with catalytic activities, it is concluded that, during catalysis, reoxidation by oxygen of the MoO 3 surface is necessary to counterbalance the reducing effect of formamide, thus restoring the catalytically active sites.

Catalytic synergy between MoO 3 and BiPO 4 in N-ethyl formamide dehydration : II. Characterization of mixtures of MoO 3 and BiPO 4

This paper concerns the physicochemical characterization of mixtures of BiPO 4 and MoO 3 powders whose catalytic activity in the dehydration of N-ethyl formamide has been reported previously. The aim of the work was to investigate whether the existence of any mixed BiPMo oxide species, due to a contamination of the surface of one phase by elements coming from the other phase, could explain the synergy. Analytical Electron Microscopy (AEM) detects a contamination of BiPO 4 by MoO 3 only when the mixture is prepared from suspensions of BiPO 4 and MoO 3 in water. Electron Spectroscopy for Chemical Analysis-X-Ray Photoelectron Spectroscopy (ESCA-XPS) results cannot give any valuable information with respect to contamination, due to the relatively important thickness of the surface layer analyzed. Ion Scattering Spectroscopy shows a contamination in the same case as AEM. The MoO 3-contaminated layer is easily removed by ion sputtering. We conclude that, except for the fresh mixture prepared with water, no surface contamination of one phase by elements of the other phase can be detected in fresh catalysts or in catalysts having worked in the reacting mixture of N-ethyl formamide and oxygen at moderate temperatures.

Catalytic synergy between MoO 3 and BiPO 4 in N-ethyl formamide dehydration : I. Catalytic properties, reducibility, and reoxidizability of mixtures of MoO 3 and BiPO 4

In previous publications, we reported that a catalyst composed of BiPO 4 and MoO 3 is active in the dehydration of formamides to nitriles. Some molecular oxygen in the feed is necessary for maintaining the catalyst active and selective. We report here results obtained with catalysts of different compositions prepared by mixing, by three different methods, separately prepared powders of BiPO 4 and MoO 3. The mixtures are more active than the single components. They are reduced more easily under a high vacuum or in the presence of oxygen and they reoxidize subsequently more rapidly. A decrease of the oxygen pressure, during catalysis, depresses the magnitude of the synergetic effect, changing more the activity of the MoO 3-rich mixtures. The possible interpretations of the synergy are discussed. It is concluded that the synergy could be due to a remote control mechanism, whereby BiPO 4 probably produces a mobile oxygen species which, by spill-over onto MoO 3, restores catalytically active centers on this latter. The effects observed in reduction experiments are explained by a reverse spill-over.