Sven Kureti

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.

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.

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.

Kinetic Modelling of the Adsorption and Desorption of NH3 on Fe/BEA Zeolite

Abstract This paper deals with the kinetic modelling of the adsorption and desorption of NH3 on Fe/BEA zeolite. Fe/BEA was recently reported to show high activity for the selective catalytic reduction (SCR) of NOx by NH3. The NH3 adsorption and desorption kinetics was examined in the temperature range from 323 to 923 K using temperature programmed desorption of NH3 (NH3-TPD) and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). With these investigations an elementary kinetic mean field model of the NH3 adsorption and desorption was constructed employing Arrhenius-based rate expressions. The model differentiated molecularly bound NH3 and NH4+ surface species originated from the NH3 chemisorption. For both kinds of species, the kinetic parameters of the adsorption of NH3 were adopted from the literature, while that of the desorption were numerically fitted based upon NH3-TPD traces. The reliability of the kinetic model was evidenced by reproduction and prediction of the NH3-TPD profiles as well as thermodynamic consistency.

Elementary Kinetic Mean Field Modelling of the Lean NOx Reduction by H2 on Pt/WO3/ZrO2 Catalyst

This paper deals with the elementary kinetic mean field modelling of the catalytic NOx reduction by H2 on Pt/WO3/ZrO2 under oxygen-rich conditions. Pt/WO3/ZrO2 exhibits outstanding deNOx activity at low exhaust temperatures as well as improved N2 selectivity as compared with classical Pt catalysts. The kinetic model was developed based upon a postulated reaction mechanism as well as kinetic examinations and implied a network of 48 reaction steps described by Arrhenius-based rate expressions. Kinetic parameters were taken from literature and were elucidated by fitting calculations, while pre-exponential factors of adsorption were estimated from kinetic gas theory. For validation, catalytic studies were simulated and compared with experiments and thermodynamic consistency was proven. As a result of the kinetic model, the formation of OH surface species was identified as the rate determining step of H2 oxidation, while the reduction of NO predominately occurs by dissociation of chemisorbed NO.