Werner Weisweiler

Simultaneous conversion of nitrogen oxides and soot into nitrogen and carbon dioxide over iron containing oxide catalysts in diesel exhaust gas

Abstract This paper deals with the simultaneous catalytic conversion of NO x and soot into N 2 and CO 2 in diesel exhaust gas. Several iron containing oxide catalysts were partially modified by the alkali metal potassium and were used for NO x –soot reaction in a model exhaust gas. Fe 1.9 K 0.1 O 3 has shown highest catalytic performance for N 2 formation in the so far investigated catalysts. Further studies have shown that Fe 1.9 K 0.1 O 3 was deactivated in a substantial way after about 20 TPR experiments due to the agglomeration of the promoter potassium. Experiments carried out over the aged Fe 1.9 K 0.1 O 3 catalyst have shown that NO x –soot reaction was suppressed at higher O 2 concentration, since O 2 –soot conversion was kinetically favored. In contrast to that, the catalytic activity was increased in presence of NO 2 and H 2 O. Mechanistic examinations suggest that (CO) intermediates, formed at the soot surface, are the reactive sites in the NO x –soot reaction. Higher catalytic performance in presence of NO 2 could be explained by the enhanced formation of these (CO) species. Moreover, nitrate species formed at the catalyst surface might also play an important role in NO x –soot conversion.

Catalytic behaviour of metal based ZSM-5 catalysts for NOx reduction with NH3 in dry and humid conditions

Abstract Some metals (Cu, Cr and Fe) based on zeolite (H-ZSM-5) catalysts were prepared by wet impregnation method. These were characterized by X-ray diffraction and surface area measurements. The reduction of NO by NH 3 in the presence of O 2 with and without water vapour was determined over these catalysts. FTIR spectra of adsorbed species and TPD study indicate the formation of copper ammonia complex; chemisorption of NH 3 and NO x is found on Cu-ZSM-5, whereas in the cases of Cr-ZSM-5 and Fe-ZSM-5, only NH 3 chemisorption is observed. Cu-ZSM-5 showed better catalytic activity with water and was superior to other catalysts, which showed lower activity and moderate selectivity. The results indicated that the presence of O 2 helps in adsorbing more NO over Cu-ZSM-5. The mechanistic pathways of this proposed reaction are based on earlier findings and on those of the present investigation.

A novel sol–gel method for the synthesis of γ-aluminium oxide: development of the sol–gel transformation and characterization of the xerogel

Abstract A novel method for the synthesis of aluminium oxide gel has been developed, whereby the sol–gel transformation was investigated. Aluminium tri- sec -butoxide was used as precursor while acetone was chosen as solvent. The synthesis was carried out in a special reactor, which allowed the dosing of steam. 27 Al NMR spectroscopy showed that during the sol–gel process the signal at δ ∼3 ppm increases strongly corresponding to the formation of hexacoordinated aluminium species. Beside hydrolysis and condensation reactions, the coordination of acetone to a strong Lewis acid aluminium site occurs, which was shown by FTIR and 27 Al NMR spectroscopy. Viscosimetric analysis showed that at the beginning of the sol–gel process short polymers are observed while before the gelation a three-dimensional polymer network is formed. After pyrolyzing the gel a high surface area γ-aluminium oxide xerogel was formed. The effect of heating on the morphology and structure was examined by nitrogen physisorption (BET and pore size distribution), XRD and 27 Al MAS NMR spectroscopy.

Absorption of nitrogen monoxide in aqueous solutions containing sulfite and transition-metal chelates such as Fe (II)-EDTA, Fe (II)-NTA, Co (II)-Trien and Co (II)-Treten

For wet denitrification processes nitrogen monoxide is the crucial component owing to its low water solubility. By addition of transition-metal complexes, able to form nitrosyls, the effective NO concentration in the liquid phase is enhanced. Kinetic (reaction orders and rate constants) as well as thermodynamic (stability constants) data for nitrosylation have been established. It has been found that Fe(II)-EDTA and Fe(II)-NTA react very fast to form stable NO complexes and are widely pH independent. The formation of Fe(III)-EDTA nitrosyl is found to be rapid, but the large deviation in the measured data prevents reliable evaluation. While the equilibrium constants of the Co(II)-trien and Co(II)-tetren nitrosyls are largely pH independent, the rate of formation is influenced markedly by pH. Each nitrosyl shows individual behavior towards sulfite. Fe(II)-EDTA and Fe(III)-EDTA exhibit the highest absorption capacities. The CO(II) polyamines convert the absorbed NO mainly to gaseous N2O rather than to liquid-phase products.

A new route for the synthesis of high surface area γ-aluminium oxide xerogel

Abstract A new sol–gel method has been developed to synthesize high surface area γ-aluminium oxide. The preparation was carried out at ambient temperature using a special reactor which allowed the dosing of gaseous water for the hydrolysis of aluminium alcoxide. Aluminium tri- sec -butoxide was used as precursor and acetone as solvent, since this mixture leads to a stable lyogel. After drying and pyrolysis a high surface area γ-aluminium oxide xerogel was formed. The effect of heating on the morphology and structure was examined by nitrogen sorption (BET and pore size distribution), SEM, XRD and 27 Al MAS NMR. The results indicate that the xerogel is a highly stable material at elevated temperatures. Moreover, the high surface area xerogel exhibits an enlarged amount of acid sites which leads to an enhanced catalytic activity for example in the propene oxidation.

Entfernung von Stickstoffoxiden aus Sauerstoff enthaltenden Automobil-Abgasen

The most important systems for downstream reduction of NO x under lean conditions of exhaust gases are discussed. The systems operate either continuously under direct chemical reduction of NO x to nitrogen, or discontinuously with prior adsorption. The selective catalytic reduction (SCR) of nitrogen oxides using ammonia (processed in an NH 3 generator) or ammonia-forming substances (urea as solution or solid) as reducing agents is almost at the application stage in trucks, while hydrocarbons as reducing agents (so-called HC-SCR) are not sufficiently selective for NO x reduction because the hydrocarbons are themselves predominantly oxidized. The principle of NO x storage as nitrates followed by regeneration and reduction to nitrogen requires no separate or external reducing agents and claims therefore to meet future emission standards as long as problematic sulfur incorporation is avoided. The common characteristics of all these NO x abatement systems is that they are all based on the principle oxidation before reduction and involve the key molecule NO 2 .

Modellgasuntersuchungen mit NH3 und Harnstoff als Reduktionsmittel fuer die katalytische NOx-Reduktion

Dem Applikationspotential der katalytischen NOx-Reduktion im Abgas von Dieselmotoren mit Kohlenwasserstoffen wurde nur geringe Attraktivitat zugeordnet. Dagegen wird dem SCR-Verfahren mit stickstoffhaltigen Reduktionsmitteln eine bemerkenswert bessere Performance eingeraumt. Zwei Meilensteine in der Weiterentwicklung dieses Verfahrens werden durch die vorliegenden Modellgasuntersuchungen in diesem Bericht, der aus einem Vorhaben der Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) hervorgeht, aufgezeigt. Eine weitere intensive Untersuchung der chemischen und verfahrenstechnischen Grundlagen wird vorausgesetzt.

Oxidation of SO2 to sulfate in sea salt aerosols

SummaryIn laboratory-scale experiments sea salt particles are exposed to SO2 at a temperature of 22°C and relative humidities of 40, 60 and 80%; the SO2 gas concentration is fixed to 0.2, 0.5 and 1.0 ppm (v), respectively. In further test series NO2 is added to the gas phase. As kinetic data the capacity values of the sea salt particles (mg formed sulfate/g dry aerosol) are determined as function of time and from this the reaction rates (mg formed sulfate/g dry aerosol and minute) are calculated in dependence of the yield. The relative humidity (r.h.) has proved to be a decisive reaction parameter. For example, the rate (at a reaction time of one hour) increases at a SO2 concentration of 0.5 ppm (v) from 0.01 to approx. 0.1 mg SO42−/g·min, if the r.h. will increase from 40 to 80%. However, the gas concentration has only an importance at high humidities (where the reaction takes place in droplets) for the sulfate formation in sea salt aerosols. If the SO2 concentration is reduced from 1.0 to 0.2 ppm (v) at a r.h. of 80%, the rate will be decreased from 0.2 to about 0.07 mg SO42−/g·min; however, at a r.h. of 60% from 0.075 to 0.04 mg SO42−/g·min. As an increased sulfate formation but no nitrate formation can be detected when NO2 is added to the gas phase, it can be assumed that SO2 is oxidized in the electrolyte layer around the sea salt particles whereas NO2 is reduced. If NO2 (SO2:NO2=1:1) is added to the gas phase, the rate — for example at a r.h. of 40% — will be increased from 0.01 to 0.24 mg SO42−/g·min.

Recovering of components from plastic bonded propellants

Economic reasons and the protection of the environment demand methods of disposal allowing to recover and re-use materials, which have been in service as well as to avoid producing unwanted or harmful substances when doing so. This also applies for propellants and explosives. Recently developed propellants contain expensive crystalline energetic materials such as the nitramines, hexogen (RDX) and octogen (HMX), bonded in a chemical three-dimensional crosslinked polyurethane matrix. These substances are called plastic bonded propellants. In order to recover the components, the polyurethane matrix is broken solvolytically with pure water and alkaline water (0.05-0.5 n NaOH) at temperatures between 130 and 170°C in a pressure cell. From a model rocket propellant, consisting of a polyetherpolyol mixture (Lupranol 1000/2021) cured with Desmodur T80 and filled with 60 mass% ammonium perchlorate (AP), 84-90% of the polyetherpolyol component was recovered, and 98% of the AP content subsequently determined in the aqueous solvolysate. The polyetherpolyols were nearly not changed at the high solvolytic stress of 170°C and 2 h, as shown by the molar mass distributions, determined by using gel permeation chromatography. The solid gun propellant KHP consisting of 86 mass% hexogen (RDX) and 14 mass% GAP-N100 binder was solvolyzed at 130, 150 and 170°C with pure water and with 0.05 n NaOH for corresponding time periods of 10, 30 and 60 min. Hexogen is recoverable with high yields and with high purity. GAP (glycidyl azide polymer) is a polyetherdiol as Lupranol 1000, formally on the basis of propane-1,2-diol with azide (N 3 ) groups attached to its lateral methyl groups. It does not behave in the same way as the Lupranol polyetherpolyols. Under exposure to solvolytic conditions, its molar mass distribution is broadened and its azide content is reduced, which was determined via infrared absorption of the asymmetric N 3 stretching vibration, and via its energy content using DSC, in both cases in relation to the azide content of the unexposed GAP. The GAP-N100 binder is not split up, GAP is not recoverable. In the splitting-off of nitrogen from the N 3 group, a nitrene functionality arises which forms solvolytically not scissionable C-N bonds by intermolecular insertion reactions. The gaseous main reaction products in the solvolysis of KHP are N 2 and N 2 O, besides a little CO 2 , O 2 and CO. NH 3 and CH 2 O were not quantified. The following ionic decomposition products were found: NO 2 - , NO 3 - , HCOO - and NH 4 + . The product spectrum can be interpreted from the mechanisms and reaction products given in the literature for the decomposition of hexogen, as well as through reactions of the decomposition products with the solvolytic agent and reactions among the decomposition products themselves.

Simulation of a driving cycle in laboratory : an approach for testing catalysts suitable for automotive exhaust NOx abatement under lean conditions

Abstract Catalyst testing for the removal of NO x under lean conditions suffers from a lack of detailed information regarding catalytic activity if reaction conditions are permanently varied due to application of a driving cycle. To overcome this fact, a new laboratory reactor system has been developed which allows the simulation of an inlet catalyst temperature profile of the MVEuro2 driving cycle in the laboratory. The new reactor offers a non ambiguous and inexpensive method for testing catalysts under controlled dynamic conditions.