Kinetics vanadium catalysts

Balzhinimaev, B. S., Belyeava. N. P., and Ivanov, A. A., Kinetics of dissolution of inactive crystalline phase in vanadium catalysts for S02 oxidation. React. Kinet. Catal. Letters 29, 465-472 (1985). 

The Kinetics of Ammoxidation of Xylenes over Vanadium Catalysts... 

The kinetics of the ammoxidation of xylenes over a vanadium catalyst and mixed vanadium catalysts were studied. The reaction rate data obtained were correlated with the parallel consecutive reaction scheme by the rate equations based upon the Langmuir-Hinshelwood mechanism where the adsorption of xylenes was strong. The reaction rates of each path are remarkably affected by the kind of xylene and catalyst. The results of the physical measurement of catalysts indicated that the activity and the selectivity of reaction were affected by the nature and the distribution of metal ions and oxygen ion on catalyst surface. 

Recently, the kinetics of the ammoxidation of m-xylene (1) and xylene isomers (2) over vanadium catalyst, and of m-xylene over mixed vanadium catalysts (3) were reported. This paper summarizes the results concerning the specific rate constants for each reaction path obtained in the above studies and adds some data on physical properties of each catalyst. 

The Oxidation of Sulphur Dioxide. - This very important reaction is probably the oldest one in which vanadium catalysts have been used in practice. It is generally assumed that in these catalysts the vanadium is present dissolved in a liquid mixture of alkali metal meta- and/or pyro-sulphates. Villadsen and Livbjerg3 recently reviewed the properties of these supported liquid phase catalysts and showed that a number of questions still remain unanswered. Urbanek et al.la and Kenney75 presented reviews of the catalytic oxidation of S02, considering both the kinetics and problems of industrial reaction design. 

B.S. Balzhinimaev, V.E. Ponomarev, N.P. Belyaeva, A.A. Ivanonv. G.K. Boreskov, Studies of fast relaxations in SO2 oxidation on active components of vanadium catalysts. React. Kinet. Catal. Utt. 30 23 (1991). 

A limited kinetic investigation has been carried out on promotors for vanadium catalysts (VO(Ot-Bu)3/Al2Et3Cl3) in ethylene polymerization [234]. It was shown that esters of trichloroacetic acid, added continuously during the polymerization, reactivated the catalyst and permitted polymerization to be carried out at 120°C. Under these circumstances over 250 polymer chains were produced per vanadium atom and the polymers had /Mn ratios close to 2.0, which would be anticipated for a single catalytic entity. 

The ratio of parallel to consecutive reaction rates is a function of the hydrocarbon structure, the catalyst type, and the reaction temperature. In studying the kinetics of catalytic benzene oxidation to maleic anhydride Hammar (107) came to the conclusion that benzene oxidizes by two independent routes the formation of maleic anhydride, and the complete combustion to carbon dioxide and water via unidentified intermediates. He suggested the following scheme for benzene oxidation over a vanadium catalyst ... 

Certain information on the kinetics of naphthalene oxidation over various vanadium catalysts is given in the review by Dixon and Long-field (110). This reaction was found to vary from zero to first order with respect to naphthalene, and be close to first order for oxygen. 

Ciainbelli, P. Parrella, P. and Vaccaro, S., Kinetics of soot oxidation on potassium-copper-vanadium catalyst, In Catalysis and Automotive Pollution Control II, (Ed Crucq, A.) Elsevier Science Publishers,... 

Hanada, R., Egi, M., Fujiwara, N., and Akai, S. (2010) Dynamic kinetic resolution of allyl alcohols by the combined use of lipases and vanadium catalysts application to various substrates. Paci-fichem 2010, International Chemical Congress of Pacific Basin Societies, Honolulu, HI, December 15-20, 2010 ORGN-1978. 

The reaction of di- -butylsulfide with r-butyl hydroperoxide proceeds at a convenient rate in ethanol at 25 °C in the presence of catalytic quantities of bisacetyl-acetonato-oxovanadium(IV) [VO(acac)2] affording di-n-butylsulfoxide in quantitative yield [146]. The kinetics of this reaction have been examined in detail. With [r-BuOOH]o/[VO(acac)2] >8 and [VO(acac)2]o = 1 x 10 to 2 x 10 M the reaction is first order in sulfide and first order in vanadium catalyst, equation (97). 

The sequence of reactions expressed by equations (99)-(104) is consistent with the observations made in this study. In fact, the kinetic first-order dependence on sulfide, hydroperoxide, and vanadium catalyst which was observed implies that one molecule of each reactant is involved in the transition state of the rate-determining step. 

Analysis of the dynamics of SCR catalysts is also very important. It has been shown that surface heterogeneity must be considered to describe transient kinetics of NH3 adsorption-desorption and that the rate of NO conversion does not depend on the ammonia surface coverage above a critical value [79], There is probably a reservoir of adsorbed species which may migrate during the catalytic reaction to the active vanadium sites. It was also noted in these studies that ammonia desorption is a much slower process than ammonia adsorption, the rate of the latter being comparable to that of the surface reaction. In the S02 oxidation on the same catalysts, it was also noted in transient experiments [80] that the build up/depletion of sulphates at the catalyst surface is rate controlling in S02 oxidation. 

Through the years, several catalyst formulations have been employed, but one of the traditional catalytic agents has been vanadium pentoxide. Calderbank (114) has indicated that for a catalyst consisting of V205 supported on silica gel, the kinetic data are represented by a rate expression of the form... 

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

Kinetic expressions for the three step pathway given above for the partial oxidation of methane to formaldehyde over a vanadium oxide-silica catalyst were determined by Spencer and Periera [17]. The kinetic parameters... 

They focus on the ID simulation of an urea SCR system. The system includes a model for N02 production on a DOC, a model for urea injection, urea decomposition and hydrolysis catalyst, a model for a vanadium-type SCR catalyst and a model for NH3 decomposition on a clean-up catalyst. The catalyst models consist of a ID monolith model with global kinetic reactions on the washcoat surface, kinetic parameters have been taken from literature or adjusted to experimental data from literature. The complete model was implemented in AVL BOOST (2006). AVL BOOST is an engine cycle and gas exchange simulation software tool, which allows for the building of a model of the entire engine. 

In the first stage of the investigation the catalyst can be considered in the form of powder in order to derive intrinsic transient kinetics of all the relevant reactive processes. To this purpose, dynamic reactive experiments can be performed in a simple tubular fixed-bed microreactor over small quantities (50-200 mg) of finely powdered catalyst in principle, this guarantees negligible transport limitations and more controlled conditions (e.g. isothermal catalyst bed), hence enabling a direct estimation of intrinsic rate parameters by kinetic fit. Internal diffusion limitations are particularly relevant to the case of bulk (extruded) monolith catalysts, such as vanadium-based systems for NH3/urea SCR however, they... 

The MR rate law relies on the assumption that the SCR reaction is governed by a redox mechanism and therefore predicts a kinetic dependence on oxygen. It has been derived assuming that (i) two types of sites for NH3 adsorption (acidic non-reducible sites) and for NO + NH3 activation/reaction (redox sites, associated with vanadium), respectively, prevail on the catalyst surface (ii) NH3 blocks the redox sites (iii) reoxidation of the redox sites is rate controlling. 

The great variations in the reaction kinetics using a vanadium oxide catalyst for each xylene are shown by the relative ratios for the direct... 

In Section IV, the kinetics and mechanisms of catalytic HDM reactions are presented. Reaction pathways and the interplay of kinetic rate processes and molecular diffusion processes are discussed and compared for demetallation of nickel and vanadium species. Model compound HDM studies are reviewed first to provide fundamental insight into the complex processes occurring with petroleum residua. The effects of feed composition, competitive reactions, and reaction conditions are discussed. Since development of an understanding of the kinetics of metal removal is important from the standpoint of catalyst lifetime, the effect of catalyst properties on reaction kinetics and on the resulting metal deposition profiles in hydroprocessing catalysts are discussed. 

A summary of hydrodemetallation kinetic studies is presented in Table XXVI. The list is not exhaustive but does include a diversity of feedstocks and catalysts. It is apparent that a discrepancy in reaction order rt with respect to total metal (Ni or V) concentration has been observed. Riley (1978) reported first-order kinetics for both nickel and vanadium removal when hydrotreating a Safaniya atmospheric residuum. Demetallation kinetic order of 1.0 to 1.5 depending on reactor configuration has been reported by van Dongen et al. (1980) for vanadium removal. Oleck and Sherry (1977) report a better description of the reaction system is obtained with second-order kinetics for nickel and vanadium removal from Lago-medio (Venezuelan) atmospheric residuum. All studies were conducted on CoMo/A1203 catalysts. 

A vanadium complex with C2-symmetric bishydroxamic acids catalyses the epox-idation of allylic alcohols with ees up to 97% and excellent yields. The catalysts have been used for kinetic resolution of secondary allylic alcohols with high ee. The structure of a possible intermediate has been suggested.38... 

Reduction of Nitric Oxide with Ammonia. - Control of the emission of NO from stationary sources is possible by selective catalytic reduction, for which up to now NH3 is the only effective reductant in the presence of excess 02. Beside noble metal catalysts Bauerle etal.101 109 and Wu and Nobe108 studied Al2 03-supported vanadium oxide and found this to be highly effective in NO removal which is considerably enhanced by the presence of 02. Alkali metal compounds which are usually added as promoters for S02 oxidation completely inactivate the catalysts for NO reduction. Adsorption kinetic studies indicated first-order dependence on NH3 adsorption. Similar results were obtained for NO on reduced vanadium oxide, but its adsorption on... 

Vanadyl Phosphate Catalysts. — For the oxidation of C4-hydrocarbons to maleic anhydride, vanadyl phosphate catalysts with a variety of V P ratios and different additives have been proposed. Nakamura etal.123 observed for V P = 1 2, an average oxidation number of four for vanadium, highly aggregated vanadium ions and a high selectivity. Varma and Saraf124 also studied this reaction and on the basis of kinetic results propose a two-stage redox mechanism. They also concluded that maleic anhydride is hardly oxidized to carbon oxides, which are mainly formed in a side reaction from the original... 

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