Kinetic CharacterizationSynthesis Catalyst Design of a Novel VO x /WO x Catalyst for the Oxidative Dehydrogenation of Propane Isabelle Ascoop †,*, Vladimir V. Galvita *, An Verberckmoes ¥, Guy B. Marin * and Pascal Van Der Voort † Introduction I.A. is grateful to the Long Term Structural Methusalem grant nr. 01M00409 Funding by the Flemish Government. † COMOC (Center for Ordered Materials Organometallics & Catalysis) Department of Inorganic and Physical Chemistry, Krijgslaan 281 (S3), 9000 Ghent, Belgium, University of Ghent * LCT (Laboratory for Chemical Technology) Department of Chemical Engineering, Technologiepark 914, 9052 Ghent, Belgium, University of Ghent ¥ INCAT (INdustrial Catalysis and Adsorption Technology), Faculty of Engineering and Architecture, Valentin Vaerwyckweg 1, 9000 Ghent, University of Ghent Acknowledgments The Oxidative Dehydrogenation (ODH) process has great potential to provide an answer to the increasing propylene consumption. ODH is the most attractive selective alkane converting process due to its exothermic characteristic and the lack of thermodynamic limitations in comparison with steam cracking, fluid catalytic cracking and catalytic dehydrogenation. Until now a trial design of a vanadium-tungsten oxide impregnated in silicagel has been synthesized and tested on its catalytic activity and selectivity. This type of catalyst is a testcase for the future development of mesoporous titania supported VO x /WO x catalysts. : VO x : WO x : VO x-1 OXIDATION O 2, CO 2 OXIDATION O 2, CO 2 ODH Figure 1: ODH of propane via a Mars van Krevelen mechanism. SILICAGEL (KG 60) IMPREGNATED SILICA VO x -WO x /SiO 2 INCIPIENT WETNESS IMPREGNATION CALCINATION NH 4 VO 3, (NH 4 ) 10 H 2 (W 2 O 7 ) 6 Structural Characterization SampleSelectivitySpace Time Yield (mol.s -1.g -1 ) 2 VO x /SiO 2 4,28%2, VOx-WO x /SiO 2 5,49%2, VOx-WO x /SiO 2 7,16%3, Figure 2: Raman spectra of VO x impregnated samples. Figure 2 shows that V 2 O 5 cluster formation starts at 5,7 w% of vanadium. Figure 3: Raman spectra of VO x -WO x impregnated samples. Addition of WO x hinders the formation of V 2 O 5 clusters for the same impregnated concentration. Figure 3 shows no V 2 O 5 vibrations. Diffractions of V 2 O 5 are not visible in the XRD due to the small size of the V 2 O 5 crystallites (see Figure 4). Even the TEM images don’t show any crystallites (see Figure 5). Figure 4: XRD diffractogram of the 2 VO x /SiO 2 sample. Figure 5: TEM image of the 2 VO x /SiO 2 sample. The bulk V 2 O 5 shows two distinctive peaks in the H 2 -TPR, due to respectively the terminal and apical oxygens. Although the highly loaded VO x on silica catalyst, 5,7w% of vanadium, show clearly the formation of V 2 O 5 crystallites in Raman, this is not reflected in the TPR profile (see Figure 6). Addition of WO x to VO x does not influence the T max and the presence of WO x has no effect on the reactivity of the VO x sites during H 2 -TPR (Figure 7). Although there is no change in T max, the presence of tungsten does increase the selectivity towards propylene (see Table above) and thus the overall yield. Table 1: ICP results of synthesized VO x and VO x /WO x catalysts. Table 2: Selectivity and space time yield at 550°C, calculated by the use of TPR with a heating rate of 20°C/min. Figure 6: H 2 -TPR of VO x impregnated samples. SampleICP analysis vanadium ICP analysis tungsten 1 VO x /SiO 2 3,2 w%0,63 mmol/g 2 VO x /SiO 2 5,7 w%1,12 mmol/g VOx-WO x /SiO 2 3,4 w%0,65 mmol/g1,5 w%0,08 mmol/g VOx-WO x /SiO 2 4,1 w%0,80 mmol/g4,5 w%0,25 mmol/g VOx-WO x /SiO 2 3,3 w%0,65 mmol/g6,8 w%0,37 mmol/g Figure 7: H 2 -TPR of VO x -WO x impregnated samples.