Ulrich Göbel

Oxidation of butane and butadiene to furan over vanadia–silica mixed oxides

Abstract Vanadia–silica mixed oxides (aerogels and xerogels), derived from the sol–gel preparation route, were tested in the partial oxidation of n -butane and 1,3-butadiene to furan. The dependence of the furan selectivity on morphological properties and vanadium dispersion in the silica matrix has been studied. The catalysts were characterized by N 2 and Ar physisorption, AAS, XPS and FTIR spectroscopy. Surface acidic centers of the materials were assessed by means of DRIFT-measurements of adsorbed NH 3 probe molecules. The structural properties, mainly influenced by the drying procedure of the sol–gel samples, had a major influence on the catalytic performance of the sol–gel materials. Aerogels were the most selective catalyst, converting butane to furan with only 3% selectivity. The maximum furan selectivity in butadiene transformation was about 25%, but considerable coke formation was also observed. Microporosity, found in conventionally dried sol–gel materials seems to be unfavorable for furan selectivity. The presence of Bronsted acidic sites was proved to be necessary for furan formation. Studies involving V 2 O 5 , SiO 2 , and vanadia–silica low-temperature aerogels with 5–20% vanadia contents revealed that the selectivity to furan was diminished by silica due to its intrinsic high activity for total oxidation and cracking. A comparison to literature data indicated that vanadia–silica mixed oxides and vanadia grafted on silica are markedly less selective towards furan than VPO catalysts.

Preparation of thin silver films on mica studied by XRD and AFM

Abstract Thin silver films (50–300 nm) were grown on muscovite mica at different substrate temperatures (480–600 K). The films were studied by XRD showing two different orientations. The single crystalline islands are preferentially oriented in [111] direction with a smaller quantity in [100] direction, which is also reflected by the morphology (determined by AFM) and by the oxygen content on the surface (detected by XPS). Both orientations could be traced back to two differently shaped islands: hexagonal-like flat particles and oval shaped higher ones. The orientation as well as the proportion between both species is strongly dependent on the temperature and the film thickness. In this way the conditions were optimized for preparing well-oriented thin films with large flat areas. Depending on the preparation of the films different oxygen contents were analyzed by XPS. Higher oxygen contents were found for samples with significant contributions of (100) planes.

Dauerhaltbarkeit von NOx-Nachbehandlungssystemen für Dieselmotoren

Als nachstes Ziel in der Weiterentwicklung von NOx-Speicherkatalysatoren steht die Erfullung der strengen Tier-2-Bin5-Grenzwerte im Fokus. Zur Erreichung dieses anspruchsvollen Ziels ist es notwendig, die Dauerhaltbarkeit des NOx-Speicherkatalysators weiter zu verbessern. Zwei Alterungsmechanismen sind in diesem Zusammenhang ausschlaggebend: die Vergiftung durch Schwefel und die thermische Schadigung des Speicherkatalysators. Beide Alterungsmechanismen sind nicht unabhangig voneinander, da der Katalysator wahrend den regelmasig durchzufuhrenden Entschwefelungen einer hohen thermischen Belastung ausgesetzt ist. Untersuchungen bei Umicore zeigen, wie durch eine deutliche Verbesserung des Entschwefelungsverhaltens, kombiniert mit einer verbesserten Entschweflungsstrategie des NOx-Speicherkatalysators, die thermische Belastung deutlich reduziert werden konnte und damit eine verbesserte Dauerhaltbarkeit gewahrleistet werden kann.