Nanoparticles of Ce1-xMxO2-delta (M = Ca or Zr) coated with Al2O3 with average crystallite size of 10 nm have been synthesised via solution chemistry approach under controlled chemical and hydrodynamic conditions. Their synthesis has been accomplished in three major steps: (1) simultaneous co-precipitation of cations, (2) sequential precipitation of Al(OH)(3) over the former particles and (3) calcination of the precipitated precursors to the corresponding oxides. Several compositions have been synthesised and their physicochemical properties are compared with commercial state-of-the-art material. The Al2O3-coating hinders the particles growth at high temperatures, resulting in materials with a large specific surface area and a restrain in the decrease of their oxygen storage capacity. (C) 2008 Elsevier Ltd. All rights reserved.

Bei Abgasreinigungsanlagen fur die Verminderung der Stickoxide im mageren Abgas von Verbrennungsmotoren durch selektive katalytische Reduktion mittels Ammoniak kommt es bei Uberdosierung des Ammoniaks zu unerwunschten Emissionen von nicht verbrauchtem Ammoniak. Diese Emissionen konnen mit Ammoniak-Sperrkatalysatoren vermindert werden. Ammoniak wird von diesen Katalysatoren im Idealfall zu Stickstoff und Wasser oxidiert. Diese benotigen zusatzlichen Bauraum in der Abgasreinigungsanlage, der gegebenenfalls aus dem fur den SCR-Hauptkatalysator vorgesehenen Bauraum abgezweigt werden mus. Auserdem kann es beim Einsatz solcher Ammoniak-Sperrkatalysatoren zur Uberoxidation des Ammoniaks zu Stickoxiden kommen. Um diese Nachteile zu umgehen, wird ein Katalysator zur Entfernung von Stickstoffhaltigen Schadgasen aus Dieselabgas vorgeschlagen, der zwei ubereinanderliegenden Schichten enthalt. Die untere Schicht enthalt einen Oxidationskatalysator, die obere Schicht kann mindestens 20 Milliliter Ammoniak pro Gramm Katalysatormaterial speichern. Dieser Katalysator zeigt einen verminderten Ammoniak-Schlupf bei guten SCR-Umsatzen im Tieftemperaturbereich. Er kann als SCR-Katalysator mit vermindertem Ammoniak-Schlupf oder als Ammoniak-Sperrkatalysator eingesetzt werden.

Fe-ZSM5 was prepared with high iron content by solid-state ion exchange and characterized by ICP-AES, BET surface measurements, TEM, UV–vis, EPR and DRIFT spectroscopy as well as supplementing catalytic tests in order to clear up its functionality in urea-SCR. Due to the over-exchange with iron small Fe2O3 particles were formed, identified by UV–vis, EPR and TEM measurements, which were proved to be not active for the SCR reaction. However, the oxidation of NO to NO2 over Fe3+ ions in the catalyst was realized to be a pre-requisite for the SCR reaction and the rate-determining step. DRIFT investigations under SCR conditions showed adsorbates on Fe2+ up to 300°C. The high SCR activity above 300°C can be explained by the faster reoxidation of Fe2+ to Fe3+ sites at high temperatures. The observed inhibition of the SCR reaction by excess ammonia at low and intermediate temperatures can be explained in this context by the reducing properties of ammonia converting Fe3+ to Fe2+ or by preventing the reoxidation of Fe2+.

The dynamic behaviour of the NO SCR-reaction on Fe-exchanged zeolites was investigated by the transient response method (TRM). The results were used to develop a mathematical model for catalysts containing Fe-exchanged zeolites capable of describing the dynamic phenomena observed.

The influence of NO2 on the selective catalytic reduction (SCR) of NO with ammonia was studied over Fe-ZSM5 coated on cordierite monolith. NO2 in the feed drastically enhanced the NOx removal efficiency (DeNOx) up to 600°C, whereas the promoting effect was most pronounced at the low temperature end. The maximum activity was found for NO2/NOx=50%, which is explained by the stoichiometry of the actual SCR reaction over Fe-ZSM5, requiring a NH3:NO:NO2 ratio of 2:1:1. In this context, it is a special feature of Fe-ZSM5 to keep this activity level almost up to NO2/NOx=100%. The addition of NO2 to the feed gas was always accompanied by the production of N2O at lower and intermediate temperatures. The absence of N2O at the high temperature end is explained by the N2O decomposition and N2O-SCR reaction. Water and oxygen influence the SCR reaction indirectly. Oxygen enhances the oxidation of NO to NO2 and water suppresses the oxidation of NO to NO2, which is an essential preceding step of the actual SCR reaction for NO2/NOx<50%. DRIFT spectra of the catalyst under different pre-treatment and operating conditions suggest a common intermediate, from which the main product N2 is formed with NO and the side-product N2O by reaction with gas phase NO2.

Chemie Ingenieur TechnikVolume 78, Issue 9 p. 1246-1246 VortragFree Access Transiente Effekte der NH3-SCR an Fe-Zeolithen – Experimente und Computersimulation A. Schuler Dipl.-Ing., A. Schuler Dipl.-Ing. anke.schuler@eu.umicore.com Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorA. Drochner Dr., A. Drochner Dr. Ernst-Berl-Institut für Technische und Makromolekulare Chemie, TU-Darmstadt, Petersenstraße 20, D-64287 DarmstadtSearch for more papers by this authorH. Vogel Prof. Dr.-Ing., H. Vogel Prof. Dr.-Ing. Ernst-Berl-Institut für Technische und Makromolekulare Chemie, TU-Darmstadt, Petersenstraße 20, D-64287 DarmstadtSearch for more papers by this authorS. Malmberg Dipl.-Ing., S. Malmberg Dipl.-Ing. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorM. Votsmeier Dr., M. Votsmeier Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorJ. Gieshoff Dr., J. Gieshoff Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorN. Söger Dr., N. Söger Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorL. Mußmann Dr., L. Mußmann Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this author A. Schuler Dipl.-Ing., A. Schuler Dipl.-Ing. anke.schuler@eu.umicore.com Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorA. Drochner Dr., A. Drochner Dr. Ernst-Berl-Institut für Technische und Makromolekulare Chemie, TU-Darmstadt, Petersenstraße 20, D-64287 DarmstadtSearch for more papers by this authorH. Vogel Prof. Dr.-Ing., H. Vogel Prof. Dr.-Ing. Ernst-Berl-Institut für Technische und Makromolekulare Chemie, TU-Darmstadt, Petersenstraße 20, D-64287 DarmstadtSearch for more papers by this authorS. Malmberg Dipl.-Ing., S. Malmberg Dipl.-Ing. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorM. Votsmeier Dr., M. Votsmeier Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorJ. Gieshoff Dr., J. Gieshoff Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorN. Söger Dr., N. Söger Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this authorL. Mußmann Dr., L. Mußmann Dr. Umicore AG & Co. KG, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangSearch for more papers by this author First published: 06 September 2006 https://doi.org/10.1002/cite.200650124Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume78, Issue9Special Issue: GVC/DECHEMA-Jahrestagungen 2006 mit 24. DECHEMA-Jahrestagung der BiotechnologenSeptember, 2006Pages 1246-1246 ReferencesRelatedInformation

Fe-ZSM5 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with ammonia over a broad temperature range, applying simulated diesel exhaust gas conditions. The catalyst exhibited over 80% NOx reduction (DeNOx) from 400 to 650°C at very good selectivity. The dosage of variable amounts of ammonia in the catalytic tests revealed that the SCR reaction is inhibited by ammonia. At very high temperatures DeNOx is reduced due to the selective catalytic oxidation (SCO) of ammonia to nitrogen and the oxidation to NO. Water-free experiments resulted in generally higher DeNOx values, which are explained by the inhibiting effect of water on the NO oxidation capability of Fe-ZSM5. The catalyst was stable upon thermal ageing and only 5–15% loss in DeNOx activity was observed after hydrothermal treatment. This loss in DeNOx is in parallel with a loss of ammonia storage capacity of the aged catalyst. Characterization by NH3 TPD and MAS 27Al NMR spectroscopy revealed dealumination of the zeolite by hydrothermal ageing, which reduces the Brønsted acidity of the catalyst.

Particulate filters are currently the method of choice for reducing soot levels in diesel exhaust to the extremely low levels required for meeting future emission standards. For cost effective, reliable and manageable soot regeneration, the Catalytic Diesel Particulate Filter (CDPF) has proven to be one of the most promising solutions for maintaining filter performance. The activity of the CDPF can help lower soot ignition temperature thereby promoting active, oxygen-based filter regeneration. It can also facilitate passive regeneration of a filter at temperatures below 400 °C through formation of NO 2 by catalyzing the oxidation of NO. There are two important factors which affect the passive regeneration of a CDPF. One is the influence of NOx/soot ratio. The other is the deterioration of the catalytic function upon aging. Together they determine the quantity of NO 2 available for soot oxidation. In the first part of this publication the impact of model gas, engine and field aging on the catalytic performance of a state of the art CDPF (A) and newly developed CDPF (B) will be reported. A correlation is developed between aging methods and the thermal durability of these two CDPF technologies. In the second part of this paper the influence of NO x concentration on the regeneration of diesel particulate filters will be investigated on a heavy duty engine bench. Both coated and uncoated filters in fresh and aged state will be evaluated at temperatures typical of passive NO 2 and oxygen-based soot regenerations.