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Öğe Abatement of nitrous oxide over natural and iron modified natural zeolites(ELSEVIER SCIENCE BV, 2011) Ates, Ayten; Reitzmann, Andreas; Hardacre, Christopher; Yalcin, HuseyinThe natural zeolite obtained from the Sivas-Yavu region in Turkey and iron modified forms were studied for the decomposition of N(2)O and selective catalytic reduction of N(2)O with NH(3). The natural and iron modified zeolites were characterised by XRD, SEM, H(2)-TPR, NH(3)-TPD and low temperature nitrogen sorption. The effect iron loading, precursor and valency on the catalytic performance of catalysts were studied. The catalytic activity of the zeolites increased up to about 7.0 wt.% Fe. Above this value, the activity decreased as a result of a reduction in the surface area and pore volume of the zeolite. The highest catalytic activity was observed using catalysts prepared with FeCl(2) due to the formation of more reducible iron species in the zeolites. When FeSO(4) was used as the iron precursor, sulphate remained on the surface even after extensive washing resulting in a decrease in the N(2)O decomposition activity and a shift the N(2)O reduction temperature to higher values. Since the natural and iron exchanged natural zeolites prepared using FeCl(2) have comparable activity with synthetic zeolites, the offer a promising alternative catalyst for the abatement of N(2)O, particularly for the selective reduction of N(2)O with NH(3). (C) 2011 Elsevier B.V. All rights reserved.Öğe Experimental techniques for investigating the surface oxygen formation in the N2O decomposition on Fe-MFI zeolites(ELSEVIER SCIENCE SA, 2007) Ates, Ayten; Reitzmann, AndreasSeveral experimental techniques were used to investigate the formation of surface oxygen in the N2O decomposition on an Fe-MFI zeolite. These techniques consisted of multipulse and step experiments as transient methods at ambient pressure and experiments in a closed set-up of Panov and co-workers at strongly reduced pressure. The total amount of surface oxygen determined through multipulse experiments was in the range of the amount obtained in the vacuum set-up at 523 K (40-50 mu mol O g(catalyst)(-1)). In contrast, the step technique revealed considerably higher values, up to 110 mu mol O g(catalyst)(-1), indicating an accumulation of oxygen in the zeolite. This phenomenon might also be responsible for the observation that higher cat reaction temperatures increase the total amount of surface oxygen, which can be deposited in the zeolite. In contrast to experiments in the vacuum set-up, the temperature-programmed desorption after multipulse and step experiments shows the presence of various oxygen species differing in thermal stability. The influence of temperature on the rate of surface oxygen formation was determined from step and vacuum experiments. The results of the step experiments lead to a lower activation energy, 14 kJ mol(-1), than the experiments in the vacuum set-up (49 kJ mol(-1)), probably due to sorption and mass transfer effects. Comparing the rate of surface oxygen formation and of total N2O decomposition reveals that the former is very fast and not rate determining for the latter. Furthermore, the rate of total N2O decomposition seems to be inhibited by adsorbed N2O, detected in the transient experiments. This observation is considered in an adequate kinetic model. (c) 2007 Elsevier B.V. All rights reserved.Öğe Oksijen ve diazotmonooksit $(N_2O)$ ile alkanların oksidatif dehidrojenasyonu(2007) Ateş, Ayten; Reitzmann, Andreas[Abstract Not Available]Öğe Surface oxygen generated upon N2O activation on iron containing ZSM-5 type zeolites with different elemental composition(ELSEVIER SCIENCE BV, 2012) Ates, Ayten; Reitzmann, Andreas; Waters, GerritVarious ZSM-5 zeolites with iron contents ranging from of 0.86 to 4.98 and Si/Al ratios of 11.5-140 were prepared by solid-state ion exchange with FeCl2. The catalysts were characterised by XRD, H-2-TPR and NH3-TPD. The formation and stability of surface oxygen over these zeolites were investigated with a transient multipulse technique combined with subsequent temperature-programmed desorption (TPD). Higher iron contents enhance the formation of surface oxygen. However, when a critical iron content is reached, larger iron oxide clusters and particles are formed and these larger clusters do not contribute significantly to surface oxygen formation. Moreover, the amount of desorbed oxygen is more than that formed from N2O due to the additional desorption of oxygen present in the lattice of such oxide clusters. TPD studies indicate the presence of different surface oxygen species depends on both the zeolite iron content and Si/Al ratio. (C) 2012 Elsevier B.V. All rights reserved.
