Design of an Enhanced Throughput Catalytic Test System Capable of Rapid Heating and Cooling

Introduction High-throughput techniques are used in combinatorial chemistry, for example to per-mit preparation and screening of hundreds of catalysts simultaneously [1]. The prin-ciple of conducting more than one experiment at the same time is generally desir-able. Here we present a system allowing three concurrent fixed bed reactor tests, to be conducted on the laboratory scale (2 ml bed volume). This enhancement in throughput is achieved without loss of reaction analysis information. System Requirements The system is designed to investigate low temperature alkane isomerization (butane, pentane) on sulfated zirconia catalysts and therefore must fulfill the following condi-tions: (I) Isothermal over a wide temperature range, from 0°C (n-pentane isomerization) to 650°C (in situ calcination of the catalyst material [2]) (II) Rapid heating and cooling to reduce time loss (III) Fast and quantitative gas phase analysis Design and Test Results The requirements led to the construction of a reaction vessel in which three U-shaped tubular quartz reactors (inlet Ø 12 mm, outlet Ø 6 mm) are positioned sym-metrically. These tubular reactors each contain a quartz frit in the inlet tube to hold the catalyst powders. They are fixed at the top by seals made of polytetrafluorethyl-ene. Cooling the lid by an air flow avoids thermolysis of the PTFE. Isothermal heating is possible using a fluidized sand bed. The bottom of the vessel is heated electrically. It contains a frit of metal wire that supports the sand (50-70 mesh, ca. 500 ml). The sand is fluidized by air flowing through the frit (ca. 12 l/min). A 25 K/min heating ramp is possible. For experiments below room temperature the air can be cooled, e.g. by liquid nitrogen. The reaction vessel is enclosed by a cylindrical shell that can be purged by air for cooling. Thus a fast return to lower temperatures after activa-tion/calcination is guaranteed (from 450°C to 50°C in ca. 45 min). The temperature of the reactor is monitored by a thermocouple positioned in the center of the vessel and controlled by a second thermocouple close to the heating wire. A four position valve selects the outlet of either one of the three reactors, or the bypass, for analysis. Analysis of the gas phase is performed using a Micro GC (Varian CP 4900) equipped with a thermal conductivity detector, which allows separation of n-butane and isobu-tane within ca. 1 min. Cross section through the reaction vessel containing the U-shaped reactors Reaction vessel without cylindrical shell References [1] A. Hagemeyer, B. Jandeleit, Y. Liu, D.M. Poojary, H.W. Turner, A.F. Volpe Jr, W.H. Weinberg, Appl. Catal. A, 2001, 221, 23-43. [2] A. Hahn, T. Ressler, R.E. Jentoft, F.C. Jentoft, Chem. Comm., 2001, 537-538

The influence of chemical transport via vapour phase on the properties of chloride and caesium doped V-Fe mixed oxide catalysts in the oxidation of butadiene to furan

Chloride and caesium doped V-Fe mixed oxides prepared by different methods and calcined under vapour-phase transport-restricted conditions showed a high initial furan yield of up to 40 mol-% in the oxidation of butadiene. However,after only a few hours on stream a significant loss of activity and selectivity was observed. The reason for this undesirable property was investigated using different bulk and surface-sensitive characterisation methods such as x-ray diffraction, x-ray photoelectron spectroscopy, ransmission electron microscopy and chemical methods. The data obtained for the structure, morphology, and composition of the fresh and used catalysts were correlated with their activity and selectivity properties. The presence of chloride ions was found to be surprisingly necessary for the origin of furan selectivity even up to 50 %, which was however stable only for a short period of time. Chemical transport via chlorides or bromides was observed to be essential for the formation as well as the maintenance of the activity and selectivity properties of the system. The results obtained are interpreted with an assumption that the formation of volatile halides is necessary to form disperse VOx species, which act as active and selective centres for the present reaction. Models for the formation and deactivation of these centres are discussed in this work. In addition, the possible roles of caesium and iron oxides in the catalytic system are also described and disputed

Identifizierung der Realstrukturen im System VOHPO₄ x 0.5 H₂O - (VO)₂P₂O₇

Vanadylpyrophosphate werden seit langer Zeit in der selektiven Partialoxidation von n-Butan zu Maleinsäureanhydrid (MSA) eingesetzt. Entscheidend für die katalytische Aktivität sowie Selektivität gegenüber MSA ist der Syntheseweg des Precursors VOHPO4 x 0.5 H2O sowie des durch Kalzinierung erhaltenen Vanadylpyrophosphates (VO)2P2O7 [1, 2]. Ziel dieser Untersuchungen ist es, einen Beitrag zum fundamentalen Verständnis der Struktur – Wirkungsbeziehung dieser Katalysatoren in der Partialoxidation zu liefern. Hierzu wurde eingehend die Realstruktur, d.h. Defektarten wie Atompositionen und Besetzungszahlen sowie Kristallitmorphologien und Mikrospannungen in der Verbindung (VO)2P2O7 untersucht