Vanadia catalysts

Fig. 1. Rate enhancement for S02 oxidation over a commercial promoted vanadia catalyst as a function of forcing period, time average feed composition as S02 02 ratio, and forcing manipulation (1 bar and 405°C, s = 0.5). (Figure adapted from Unni et at., 1973, with permission of the authors.)...

In order to explore composition modulation of the final stage of a converter further, Briggs et al. (1978) added a second integral reactor, also holding about 30 g of the vanadia catalyst. With the preconverter in place, this system was operated on a typical feed from sulfur burning, with a S02 02 N2 composition in vol% of 10.8 15.2 74, and from a smelter effluent with a composition of 8.0 6.2 85.8. The cycled beds of vanadia catalyst were held in a fluidized sand bath at 401°C for the former feed and at 405°C for the latter one. The space velocity for both the air and the S03/S02 mixture was about 24 min 1 (STP). Table II summarizes the experimental results for the cycle periods tested. 

Several pilot plants have been built to test periodic flow direction reversal. Pilot-scale reactors with bed diameters from 1.6 to 2.8 m were operated with flow reversal for several years. The units, described by Bunimovich et al. (1984,1990) and Matros and Bunimovich (1996), handled 600 to 3000 m3/h and operated with cycle periods of 15 to 20 min. Table VIII shows the performance of these plants for different feeds and potassium oxide promoted vanadia catalysts. The SVD catalyst was granular the IK-1-4 was in the form of 5 (i.d.) x 10-mm cylinders, while the SYS catalyst was... 

Periodic Flow Reversal Model Employing the Balzhinimaev Unsteady State Kinetic Model for S02 Oxidation Over Vanadia Catalysts... 

Comparison of metal-exchanged zeolites and vanadia catalysts under standard-SCR conditions... 

A number of studies (9,10) have demonstrated that the valence of coordination of vanadium in typical vanadia catalysts changed with gas composition in contact with the catalyst. As we discuss below, changes at the surface are partially offset by transport of oxygen from interior strata of the catalyst. We believe it is the diffusion of oxygen, as an ion, which is responsible for the relaxation time observed. 

Catalyst A process for treating industrial off-gases by catalytic oxidation over a titania/vanadia catalyst. Offered by BASF. 

LAR [Low air ratio] A process for oxidizing o-xylene or naphthalene to phthalic anhydride, using a titania/vanadia catalyst containing molybdenum. Developed by Alusuisse Italia in the 1980s. A plant was operated at Valdamo, Italy, in 1984. 

Vanadia catalysts exhibit high activity and selectivity for numerous oxidation reactions. The reactions are partial oxidation of methane and methanol to formaldehyde, and oxidative dehydrogenation of propane to propene and ethane to ethcnc.62 62 The catalytic activity and selectivity of... 

Wachs, I.E. Molecular engineering of supported metal oxide catalysts Oxidation reactions over supported vanadia catalysts. Catalysis 1997,13, 37-54. 

The reactivity ot the titania supported vanadium oxide catalysts was probed by the methanol oxidation reaction. The oxidation ot methanol over the titania supported vanadia catalysts exclusively yielded tormaldehyde, 95%+, as the reaction product. The titania support in the absence ot surtace vanadia yielded dimethyl ether and trace amounts ot CO2 The almost... 

Vanadia-titania ( 5 and other supported vanadia catalysts (9) can also be applied for the production of aromatic nitriles by ammoxidation of toluene and of the three xylene isomers allumina-supported V-Sb-based oxides seem to be the best catalysts (10). Detailed kinetic studies of toluene ammoxidation have been reported recently using different vanadia-titania catalysts ( 77,72). Ammonia inhibits toluene conversion, while benzonitrile yields (up to 80 % near 610 K) are mainly limited by... 

Typical catalysts for SCR include supported vanadia, and iron or copper supported on zeolite. Here the application of a model to the design and understanding of vanadia catalyst systems is presented. Over the vanadia-based catalyst system, a Rideal-Eley approach has been adopted by most workers in the field, in which the first step is ammonia adsorption on the catalyst. This stored ammonia can then either react with NOx or be desorbed. Some important contributions to the SCR modelling literature are Andersson et al. (1994), Lietti and Forzatti (1994), Dumesic et al. (1996), Lietti et al. 

Molecular Engineering of Supported Metal Oxide Catalysts Oxidation Reactions over Supported Vanadia Catalysts ... 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

The apparent activation energies for methanol oxidation over the series of support vanadia catalysts is a composite of the activation energy and the heats of adsorption ... 

The above studies with methanol oxidation over the different supported vanadia catalysts demonstrated the dramatic effect of the specific oxide support on the reaction TOF, approximately four orders of magnitude for methanol oxidation. Several other oxidation reactions over the same series of supported vanadia catalysts were also investigated to determine if the effect of the oxide support is a general phenomenon, and the results are listed in Table 2. 

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