Journal of Catalysis 243 (2006) 82–92 www.elsevier.com/locate/jcat Ceramic foams directly-coated with flame-made V 2 O 5 /TiO 2 for synthesis of phthalic anhydride Bjoern Schimmoeller a , Heiko Schulz a , Sotiris E. Pratsinis a,∗ , Anika Bareiss b , Andreas Reitzmann b , Bettina Kraushaar-Czarnetzki b a Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland b Institute of Chemical Process Engineering, Department of Chemical Engineering and Process Engineering, University of Karlsruhe (TH), D-76128 Karlsruhe, Germany Received 4 July 2006; accepted 9 July 2006 Available online 22 August 2006 Abstract Flame-made airborne V 2 O 5 /TiO 2 nanoparticles were deposited directly onto mullite foam supports to create ready-to-use catalysts for the o-xylene conversion to phthalic anhydride. These particles containing 10% (w/w) V 2 O 5 were created by combustion of liquid precursor sprays and characterized by transmission electron microscopy, nitrogen adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and Raman spectroscopy. The specific surface area, anatase content, and dominantly monomeric vanadia species on titania were thermally stable up to 450 ◦ C. Catalyst structure was controlled in situ during deposition by the particle-laden gas flow rate through the foam, resulting in homogeneous to patchy V 2 O 5 /TiO 2 coatings. The catalytic activity and selectivity were affected by both coating texture and particle morphology. These flame- coated foams showed superior catalytic activity and selectivity at high conversions than classic, wet-made V 2 O 5 /TiO 2 catalysts.  2006 Elsevier Inc. All rights reserved. Keywords: Flame-spray pyrolysis; Direct deposition; Ceramic; Foam; Sponge; Partial oxidation; o- Xylene; Vanadia/titania; Raman spectroscopy 1. Introduction The partial oxidation of o-xylene on V 2 O 5 /TiO 2 catalysts with O 2 from air in multiple parallel fixed-bed reactors is a highly exothermic reaction (1300–1800 kJ mol −1 ) with a worldwide phthalic anhydride (PA) production of more than 3.7 million tons per year (1996) [1]. The PA is an important intermediate product in manufacture of commodity chemicals, such as modifiers for rubber and polymers. During its synthesis, evolving heat must be effectively transferred out of the catalyst bed, because hot spots above 500 ◦ C irreversibly deactivate the catalyst [2], leading to increased risk of thermal reactor run- away. Usually for this reaction, “egg-shell” vanadia/titania cat- alysts of millimeter size with solid, inert cores are packed into a fixed bed. The thickness of the catalytically active shell is typi- cally up to 100 μm [3]. This type of catalyst is used to prevent * Corresponding author. Fax: +41 44 632 1595. E-mail address: pratsinis@ptl.mavt.ethz.ch (S.E. Pratsinis). activity and PA selectivity reduction by mass transfer limita- tions inside the porous catalyst. However, high pressure drop over low-porosity (40–45%) packed beds containing these cat- alyst pellets often limits PA productivity [4]. The pellet shape affects the catalyst bed porosity; thus, hollow cylinders or rings are commonly used to keep the pressure drop as low as possi- ble [5]. An alternative approach is the application of ceramic foams as catalyst supports [6]. Such foams offer the possibility of improving reactor performance, especially for highly exother- mic and fast chemical reactions, because heat transfer is en- hanced compared with packed beds of spherical or cylindrical pellets [7]. The open-pore structure and the high void frac- tion (up to 95%) of ceramic foams lead to a lower pressure drop and increased heat transfer by radiation compared with packed beds [6]. In contrast to the laminar, separated flow in honeycombs, radial gas dispersion and higher gas turbulence is possible, increasing heat and mass transfer in the structure [6,8]. In addition, thermal conductivity and surface properties 0021-9517/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2006.07.007 First published in: EVA-STAR (Elektronisches Volltextarchiv – Scientific Articles Repository) http://digbib.ubka.uni-karlsruhe.de/volltexte/1000005744