Ascoop, Isabelle

Galvita, Vladimir

Marin, Guy

Van Der Voort, Pascal

English

Ghent University Academic Bibliography

-0,0100,010,020,030,040,050,060,070,080 100 200 300 400 500 600 700 800TCD signal (a.u.)Temperature (°C)2.0 mmol V2.0 mmol V - 0.2 mmol W2.0 mmol V - 0.6 mmol W2.0 mmol V - 1.2 mmol WAn Oxidative Dehydrogenation catalyst: a VOx/WOx catalyst on mesoporous silicaIsabelle Ascoop1, Vladimir Galvita2, Guy B. Marin2, Pascal Van Der Voort1IntroductionSynthesis1Department of Inorganic and Physical Chemistry, Center for Ordered Materials, Organometallics and Catalysis (COMOC), University of Ghent2Department of Chemical Engineering, Laboratory of Chemical Technology (LCT), University of GhentOlefins, more specific in this case propylene, are used for a great vary of chemical processes such as e.g. production of plastics (polypropylene). Due to an increase in propylene consumption for these processes there is a necessity to replace existing endothermic processes such as e.g. steam cracking to answer to this high propylene demand. Oxidative Dehydrogenation (ODH) is in comparison to these processes energetically more favorable due to its exothermic characteristic (Figure 1). Only the availability of an appropiatecatalyst with a high yield (=combined high conversion and selectivity) is lacking at this point. We are investigating a VOx/WOx catalyst supported on silica for the ODH of propane. In this part of the research program the activity of pure VOx systems are studied and compared to VOx/WOxsystems.Mesoporous silica was impregnated with a NH4VO3 solution via a dry impregnation method, Incipient Wetness Impregnation. This impregnation method only requires a NH4VO3 solution with a volume equal to the pore volume of the mesoporous material, in this case 0.75 mL/g (see Figure 2). The concentration of the NH4VO3 solution varies between 0.1 – 2.0 mmol V/g silica.VOx/WOx samples were synthesized by applying the same method with the only difference that a mixed NH4VO3 – (NH4)10H2(W2O7)6 solution was impregnated.NH4VO3 – solution:H2Ooxalic acid NH4VO3 (0.1 – 2.0 mmol)Calcination:6 hours at 500°C(heating rate: 2°C/min.) = VOxpore diameter: 5,5–6,5 nmFigure 2: Graphical presentation of the impregnation of silicagel withNH4VO3X-Ray Diffraction - XRDXRD diffractograms of all the VOx samples do not show any reflections originating from V2O5 crystals indicating that there are no detectable clusters formed even at high loadings (see Figure 3). The crystallites found in Raman are therefore very small and thus below the detection limit of the XRD (< 3 nm).Temperature Programmed Reduction - TPRH2-TPR (Figure 3) shows that the bulk V2O5 exhibits a different activity in comparison with supported VOx sites. There is no remarkable difference in reactivity with increasing loading, Tmax (~580°C) remains more or less the same.Surprisingly the 2.0 mmol VOxsample, showing crystalline peaks in Raman, does not perform differently in TPR.AcknowledgmentsI. Ascoop is grateful to the Long Term Structural Methusalem grant nr. 01M00409 Funding by the Flemish Government and Ghent University.e-mail: Isabelle.Ascoop@UGent.be http://www.we06.ugent.be/comocThe doping with WOx does not reduce the Tmax and the presence of WOx has no effect on the reactivity of the VOx sites during H2-TPR (Figure 4). It is supposed that the WOx reduces the coalescence but shows no catalytic synergy.Figure 3: H2-TPR of VOx impregnated samples.Figure 4: H2-TPR of VOx/WOx impregnatedsamples.Raman Spectroscopy0500100015002000250030003500400020040060080010001200Intensity(a.u.)Raman Shift (cm-1)0.1 mmol V0.3 mmol V0.7 mmol V1.0 mmol v2.0 mmol V0500100015002000250030003500400020040060080010001200Intensity(a.u.)Raman Shift (cm-1)2.0 mmol V2.0 mmol V - 0.2 mmol W2.0 mmol V - 0.6 mmol W2.0 mmol V - 1.2 mmol WFigure 5: Raman spectra of VOximpregnated samples. Figure 6: Raman spectra of VOx/WOximpregnated samples . Figure 5 shows the typical bands of crystalline V2O5 at a loading of 2.0 mmol V/g silica. The other samples contain isolated as well as oligomeric vanadium species.Adding WOx to the mixture reduces the coalescence of the samples. Figure 6 clearly shows that the crystalline V2O5 vibrations disappear.+H2O020040060080010001200140016000 10 20 30 40 50 60Intensity (a.u.)2θ (°)Figure 3: XRD diffractogram of  sample 2.0 mmol V/g silica.+Figure 1: ODH of propane to propylene over a VOx/WOx supported catalyst.-0,030,020,070,120,170,220 100 200 300 400 500 600 700 800TCD signal (a.u.)Temperature (°C)V2O50.1 mmol  V0.3 mmol V0.7 mmol V1.0 mmol V2.0 mmol V2.5 mmol VO2

An oxidative dehydrogenation catalyst : a VOx/WOx catalyst on mesoporous silica

https://biblio.ugent.be/publication/3165297/file/4323760

An oxidative dehydrogenation catalyst : a VOx/WOx catalyst on mesoporous silica

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