Modified Natural Zeolites as Catalysts for Catalytic Reduction of NO with CO—Main Components of Exhaust Gases (original) (raw)
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International Journal of Environmental Research, 2017
In this work, natural zeolite, clinoptilolite were treated with acid (0.6 N HCl; code ''Z-AM'') and alkaline solutions (1.5 N NaOH; code ''Z-BM''). Thereafter, nonmodified (as parent zeolite; code ''Z-NM'') and modified zeolites were impregnated with cobalt using wet incipient impregnation method (Codes: ''Z-AM-Co-0.5,1,1.5'', ''Z-BM-Co-0.5,1,1.5'', ''Z-NM-Co-0.5,1,1.5''). The prepared zeolites were characterized by XRD, ICP-OES, BET, NH 3-TPD and H 2-TPR. Also, these materials were studied for the catalytic decomposition of nitrous oxide (a greenhouse gas) to nitrogen and oxygen. The obtained results showed that the applied modifications had no significant influence (destruction) on the main structure of the zeolites including clinoptilolite, quartz and cristobalite. In addition results showed that acid modification increases the nitrous oxide decomposition because of surface area increment and the higher amount of CO/Al as well as the strong acid sites of this zeolite compared to other zeolites. Also, experiments showed that the main active species in nitrous oxide decomposition are mono-atomic (Co 2? cations) and other species exhibit much lower activity. In conclusion, natural clinoptilolite zeolites treated with acid and impregnated with Cobalt (Z-AM-CO-1.5) could be a very effective and cost-benefit catalyst for reducing N 2 O as a greenhouse gas, due to its very low price, high chemical stability and high availability.
Abatement of nitrous oxide over natural and iron modified natural zeolites
The natural zeolite obtained from the Sivas-Yavu region in Turkey and iron modified forms were studied for the decomposition of N2O and selective catalytic reduction of N2O with NH3. The natural and iron modified zeolites were characterised by XRD, SEM, H2-TPR, NH3-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 FeCl2 due to the formation of more reducible iron species in the zeolites. When FeSO4 was used as the iron precursor, sulphate remained on the surface even after extensive washing resulting in a decrease in the N2O decomposition activity and a shift the N2O reduction temperature to higher values. Since the natural a...
Journal of Catalysis, 2003
The influence of the zeolite structure on the catalytic properties for the reduction of NO with propane and propene was studied. A relation between concentration and strength of acid sites and the activity of Ni-exchanged ZSM-5, MOR, and MCM-22 was found. Ni/ZSM-5, which contains a high concentration of strong acid sites, is the most active catalyst for the NO reduction with propane. Using propene as reductant Ni/ZSM-5 and Ni/MCM-22 rapidly deactivate due to the acid site-catalyzed formation of carbonaceous deposits, while Ni/MOR is less affected by the deposits formed because of its larger pore size.
Fe-containing Zeolites as Active and Selective Catalysts for Nitrogen-oxides Reduction
2000
NO has now been revealed to be generating pollutants on a much broader scale due to its reaction with the volatile organic compounds (VOCs) which give rise to ground level (tropospheric) ozone. In this work we described the catalytic activity of Fe- Zeolites, their preparation, characterization by TPD, FTIR and XAFS used to decompose NOx to N2 by SCR system
Applied Catalysis B: Environmental, 1996
Ambient temperature SCR of NO was studied over Ti, V and B silicalite-I, silicalite-1 and H-ZSM-5 catalysts. It was observed that even at 0°C sihcalite-1 possesses some activity which falls off sharply with increasing temperature. An enhanced activity could be correlated to the titanium content in the Ti and Ti-V silicalite samples. H-ZSM-5 and H-BS-1 show an unusually high transient activity probably due to weakly adsorbed ammonia species. These would not be adsorbed at higher temperature thus explaining the decreased activity as temperature is raised. Indeed with these catalysts no transient high activity was observed when the reaction was carried out at decreasing temperatures.
Topics in Catalysis, 2018
Reduction of NO by NH 3 over metal-promoted zeolites represents the principal reaction in the selective catalytic reduction (SCR) technology for NOx removal from Diesel engine exhausts. It has been established that addition of ammonium nitrate (AN) to the reaction mixture substantially enhances the rate of this reaction, decreasing the temperature necessary for an efficient deNOx process. Nevertheless, the nature of this effect has not been completely elucidated. To investigate the NO + AN reaction mechanism, we have used individual reactants labeled with either 15 N or 18 O (or both isotopes), thus obtaining an experimental background for proposing the route of the SCR accelerated by AN addition. For this study, we have used as the catalysts H-BEA and Fe/H-BEA zeolites with various Si/Al ratios and various amounts and states of the iron species. Keywords Ammonium nitrate decomposition • NH 3-SCR mechanism • Fe-zeolites • 15 N and 18 O isotopic labeling Electronic supplementary material The online version of this article (
Applied Catalysis B: Environmental, 2003
The decomposition of N 2 O, and the catalytic reduction by NH 3 of N 2 O and N 2 O + NO, have been studied on Fe-BEA, -ZSM-5 and -FER catalysts. These catalysts were prepared by classical ion exchange and characterized by TPR after various activation treatments. Fe-FER is the most active material in the catalytic decomposition because "oxo-species" reducible at low temperature, appearing upon interaction of Fe II -zeolite with N 2 O (␣-oxygen), are formed in largest amounts with this material. The decomposition of N 2 O is promoted by addition of NH 3 , and even more with NH 3 + NO in the case of Fe-FER and -BEA. It is proposed that the NO-promoted reduction of N 2 O originated from the fast surface reaction between ␣-oxygen O * and NO * to yield NO 2 * , which in turn reacts immediately with NH 3 .
2000
The effect of a co-cation (Cs, Ba, Ca, Sr, Ba, La, Ce, Sm, Dy, Yb) on the properties of Cu exchanged faujasite catalysts in the selective catalytic reduction (SCR) of NO by NH 3 in an oxidising atmosphere has been studied. Temperature programmed reduction (TPR) by H 2 of Cu-faujasite (Cu-FAU) was used as a tool to identify and quantify the nature and location of Cu species. The 'blocking' of sodalites cages of Cu-FAU by alkali earth or lanthanide ions enhanced the SCR activity at low temperature (LT) and made the reaction fully selective towards N 2 in the whole temperature range studied (up to 773 K). The formation of N 2 O in Cu-FAU zeolites results from the reaction between nitrogen monoxide and ammonia on next-nearest-neighbour (NNN) Cu ions located in sodalite cages.