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- ItemThe Effect of Iron and Vanadium in VOy/Ce1-xFexO2-δ Catalysts in Low-Temperature Selective Catalytic Reduction of NOx by Ammonia(Weinheim : WileyY-VCH Verlag, 2020) Keller, Sonja; Agostini, Giovanni; Antoni, Hendrik; Kreyenschulte, Carsten R.; Atia, Hanan; Rabeah, Jabor; Bentrup, Ursula; Brückner, AngelikaSupported VOy/Ce1-xFexO2-δ catalysts (x=0, 0.5, 0.1, 0.2) and bare supports were prepared and tested in selective catalytic reduction (SCR) of NOx by NH3 between 150 and 300 °C with a GHSV of 70 000 h−1. Iron was found to be beneficial for the activity of the pristine supports, reaching 80 % conversion at 275 °C. When vanadium was additionally introduced into the system, iron was found to be detrimental for NOx-conversion. To derive structure-reactivity relationships, V-free supports and VOy/Ce1-xFexO2-δ catalysts were characterized by XRD, XPS, Raman spectroscopy and TEM. In situ XANES, as well as operando DRIFTS and EPR measurements were performed to study the behavior of the catalysts under reaction conditions. Up to an iron content of x=0.1, a solid Ce1-xFexO2-δ solution was formed. Higher iron contents led to formation of iron oxide agglomerates. These agglomerates, as well as an increased amount of surface oxygen species were found to be responsible for increased NOx-conversion over of pure supports. For V-containing catalysts, an interaction of Fe and V centers could be found. Under reaction conditions, Fe3+ was preferentially reduced instead of V5+, decreasing the catalytic activity of VOy/Ce1-xFexO2-δ. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemNb-modified Ce/Ti oxide catalyst for the selective catalytic reduction of NO with NH3 at low temperature(Basel : MDPI, 2018) Mosrati, Jawaher; Atia, Hanan; Eckelt, Reinhard; Lund, Henrik; Agostini, Giovanni; Bentrup, Ursula; Rockstroh, Nils; Keller, Sonja; Armbruster, Udo; Mhamdi, MouradRecently, great attention has been paid to Ceria-based materials for selective catalytic reduction (SCR) with NH3 owing to their unique redox, oxygen storage, and acid-base properties. Two series of bimetallic catalysts issued from Titania modified by Ce and Nb were prepared by the one-step sol-gel method (SG) and by the sol-gel route followed by impregnation (WI). The resulting core-shell and bulk catalysts were tested in NH3-SCR of NOx. The impregnated Nb5/Ce40/Ti100 (WI) catalyst displayed 95% NOx conversion at 200 °C (GHSV = 60,000 mL·g−1·h−1, 1000 ppm NOx, 1000 ppm NH3, 5% O2/He) without forming N2O. The catalysts were characterized by various methods including ICP-OES, N2-physisorption, XRD, Raman, NH3-TPD, DRIFTS, XPS, and H2-TPR. The results showed that the introduction of Nb decreases the surface area and strengthens the surface acidity. This behavior can be explained by the strong interaction between Ceria and Titania which generates Ce-O-Ti units, as well as a high concentration of amorphous or highly dispersed Niobia. This should be the reason for the excellent performance of the catalyst prepared by the sol-gel method followed by impregnation. Furthermore, Nb5/Ce40/Ti100 (WI) has the largest NH3 adsorption capacity, which is helpful to promote the NH3-SCR reaction. The long-term stability and the effect of H2O on the catalysts were also evaluated.