Selective catalytic reduction exchange

Brosius, R., Bazin, P., Thibault-Starzyk, F. et al., (2005) Operando FTIR study of reaction pathways of selective catalytic reduction of NOx with decane in the presence of water on iron-exchanged MFI-type zeolite, J. Catal., 234, 191. 

Kieger, S., Delahay, G. and Coq, B. (2000) Influence of co-cations in the selective catalytic reduction of NO by NH3 over copper exchanged faujasite zeolites, Appl. Catal. B 25, 1. 

Selective catalytic reduction of NOx by NH3 on V-Mo-zeolite prepared by solid-state ion exchange method... 

V-Mo-Zeolite catalysts prepared by solid-state ion exchange were studied in the selective catalytic reduction of NOx by ammonia. The catalysts were characterized by chemical analysis, X-ray powder diffraction, N2 adsorption (BET), DRIFT, UV-Vis and Raman, spectroscopy and H2 TPR. Catalytic results show that upon addition of Mo to V-ZSM-5, catalytic performance was enhanced compared to V-ZSM-5. 

Ever since the first study of metal-exchanged zeolites as new catalysts for selective catalytic reduction (SCR) of NOx with methane in the presence of oxygen was undertaken (Li and Armor, 1993), the simultaneous catalytic removal of NOx and CH4 at the exhaust of lean-bum natural gas engines has remained a challenge. 

Burch, R. and Scire, S. Selective catalytic reduction of nitric oxide with ethane and methane on some metal exchanged ZSM-5 zeolites. Appl. Catal, B Environmental,... 

Long, R. Q. and Yang, R. T. Selective Catalytic reduction of nitric oxide with ethylene on copper ion-exchanged Al-MCM-41 catalyst, Ind. Eng. Chem. Res., 1999, Volume 38, Issue 3, 873-878. 

Aqueous exchange with iron (which is very different to other techniques) led to the formation of iron nanoclusters, which were shown to be highly active in the selective catalytic reduction of NO,j. Figure 7.9 shows the suggested structures taken from ref [13]. 

Cu-MCM-41 and Cu-Al-MCM-41 samples have been obtained by ion exchange of the MCM-41 and Al-MCM-41 matrices prepared by hexadecyltrimethylammonium cloride, tetraethyl orthosilicate, aluminum isopropoxide and an ammonia solution. The aluminum concentration affects the MCM-41 textural properties and large amount of extra-framework aluminum species are supposed to be present in Al-MCM-41 with Si/Al = 30. Cu-MCM-41 and Cu-Al-MCM-41 catalysts have been tested for NO selective catalytic reduction by propane in the presence of oxygen, in comparison with microporous Cu-S-1 and Cu-ZSM-5 catalysts with similar copper loading and Si/Al atomic ratio. Cu-Al-MCM-41 catalysts are less active and selective with respect to the Cu-ZSM-5 catalysts indicating that they are not suitable for NO abatement reactions. 

Copper ions exchanged microporous molecular sieves, in particular Cu-ZSM-5, are active catalysts for the selective catalytic reduction of NO and N2O with hydrocarbons in the presence of O2 (HC-SCR). It has been reported that the catalytic activity may be controlled by intra-crystalline diffiisivity and by geometry-limited diffusion depending on the hydrocarbon molecular size and the zeolite pore size [1]. Therefore, it is of interest to prepare Cu-Al-MCM-41 mesoporous molecular sieves and to compare their activity with that of Cu-ZSM-5. 

The Cu-Al-MCM-41 catalysts where prepared by standard ion exchange procedure and tested for the selective catalytic reduction (SCR) of NO with propane in the presence of O2, under the same experimental conditions employed for Cu-ZSM-5 catalysts with similar copper loading and Si/Al atomic ratio. 

Kotter M., Lintz H.-G. and Turek T., Selective catalytic reduction of nitrogen oxide by use of the Ljungstroe air heater as reactor A case study, Chem. Eng. Sci. 47 (9/11) 2763 (1992). Lintz H.-G. and Turek T, The selective catalytic reduction of nitrogen oxides with ammonia in a catalytically active LJungstroem heat exchanger, in New Frontiers in Catalysis, Guezi et al., eds, Elsevier. Amsterdam (1993). 

Selective catalytic reduction (SCR) of NO, by hydrocarbons is under investigation as an alternative NO, removal technology. NO reduction by NHj is presently the commercial state-of-the-art technology available for reducing NO, from stationary sources and from the exhausts of lean-bum gasoline and diesel engines. A number of catalysts for the selective reduction of NO by hydrocarbons have been examined in previous studies [1-18], Transition metal ion-exchang zeolite catalysts such as mordenite and ZSM-5 are the most effective SCR catalysts. 

During investigation of cobalt-zeolite catalysts the dependence of activity on the manner by which the active phase was introduced was established. Sample of 10% CoO/H-TsVN (Si02/Al203=37) (in which cobalt was introduced by soaking) had low activity in the selective catalytic reduction of NO with CH. Conversion of 25% of NO was achieved at 320 °C, which is considerably lower than for cobalt containing cation-decationated form of zeolite with the pentasil structure, obtained by ion exchange in the solid phase (e.g., on Co-H-TsVN an 80% conversion of NO was obtained at 310 °C) [8]. 

The exceptional activity exhibited by ion-exchanged copper ZSM-5 zeolite catalysts for nitric oxide (NO) decomposition, and for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of excess oxygen is well documented [1-10]. The nature of the active copper species in the SCR reaction however still remains uncertain. We and others have recognised that there are two different types of copper species within the ZSM-5 zeolite channels [11]. Isolated copper ions exist in low symmetry environments, and small clusters, where the copper atoms are linked by extra-lattice oxygen species such as [Cu(II)-0-Cu(n)] dimers, are also present. Recent studies have also suggested that the isolated copper ions in ZSM-5 occupy two types of sites [11], which may have different SCR reactivity. It is likely... 

Stability of cerium exchanged zeolite catalysts for the selective catalytic reduction of NOx in simulated diesel exhaust gas... 

In the case of the selective catalytic reduction using ammonia as reductant but in excess 02, Ce-exchanged sodium-type mordenite (CeNa-MOR) has been reported as an active catalyst in the 250-560°C temperature range with respect to non-redox La,Na-and H-mordenite catalysts (Ito et al. 1994). In this case, the reduction of nitric oxide is thought to proceed with crucial involvement of a Ce3+/Ce4+ redox couple, although the intermediate reaction pathway depends on the reaction temperature. 

Effect of carbon number in hydrocarbon reductant on the selective catalytic reduction of NO over cation-exchanged MFI zeolites... 

A Fe(97)-BEA catalyst, prepared by conventional ion-exchange procedure and calcined at 773 K, almost contains iron-binuclear-oxo-species in charge compensation of the BEA structure. The re-oxidation of iron(II) species by N2O leads to new oxo-species reducible at lower temperature than the dimer species. Among H2, CO, propene and NH3 in the reduction of N2O, CO, propene and NH3 are selective reductants. For these three reductants a similar light-off temperature of ca 638 K is obtained in the selective catalytic reduction of N2O. It should be pointed out that CO is efficient from 473 K but its activity is limited by the reoxidation of Fe to Fe species by N2O. 

An in-situ DRIFTS study of a Fe-ZSM-5 catalyst during the selective catalytic reduction of NO by isobutane is reported. The catalyst was prepared by vapour-phase exchange of H-ZSM-5 with FeCb- Catalytic data from in a micro-catalytic flow reactor have been in principle reproduced by using the DRIFTS cell as a flow reactor. Adsorbates, transient intermediates, and interactions of zeolite OH groups have been monitored at 873-523 K, with concomitant NO conversion measurement. It has been found that the spectra of deposits formed on H-ZSM-5 and Fe-ZSM-5 are identical at 523 K. In formation about the deposits obtained at 523 K was not representative for the temperature of peak NO conversion... 

Metals other than A1 have been successfully introduced in numerous zeolite frameworks. Aluminum substitution by other metals, such as Fe, Ga, Zn, Co or Cu in the zeolite framework results in modified acidity, and subsequently modified catalytic activity, for certain reactions such as selective catalytic reduction of NOx by hydrocarbons. For example, a calorimetric and IR spectroscopic study of the adsorption of N2O and CO at 303 K on Cu(II)-exchanged ZSM-5 zeolites with different copper loadings has been performed by Rakic et al. [92]. The active sites for both N2O and CO are Cu (I) ions, which are present on the surface as a result of the pre-treatment in vacuum at 673 K. The amounts of chemisorbed species adsorbed by the investigated systems and the values of the differential heats of adsorption of both nitrous oxide (between 80 and 30 kJ mof ) and carbon monoxide (between 140 and 40 kJ mol ) demonstrate the dependence of the adsorption properties on the copper content. 

Fe —OH groups in iron-exchanged zeolites are another example of OH groups associated with a cation that can serve as an oxidant (211,536,531). It was reported that these groups are strong oxidizing agents. Even at ambient temperature, these hydroxyls oxidize NO, and at 673 K, they are reduced by CO (217,536,537). It has been proposed that Fe " —OH species are intermediates in the selective catalytic reduction of N2O by CH4 (536). 

Figure 9.3 The efficiency of cobalt-exchanged high silica stilbite (Co-TNU-10) for the selective catalytic reduction of NO to N2 with methane as a function of temperature at different inlet CH4 levels of 2400 ( ), 8000 (A) and 16000 ( ) ppm. The reactions were run with a feed containing 1200ppm NO, 2.6% O2 and 10% H2O at a GHSV of 14000h 1. [Reproduced from reference 36 with permission. Copyright 2004 American Chemical Society.]...

Although the main applications of zeohtic sohds in catalysis will continue to be as solid acids in the synthesis and transformations of petrochemicals and commodity chemicals they continue to be considered as catalysts and catalyst supports for a range of reactions of synthetic and industrial relevance. The most important of these are of titanium- and tin-containing solids in selective oxidations. Other well-studied reactions over zeohtes include light hydrocar-bons-to-aromatics (Ga-zeolites) selective catalytic reduction of NO (transition metal exchanged zeolites) C C bond formation (Pd zeohtes) selective alkane oxyfunctionalisation with air (MAPOs, M Mn, Fe, Co) and chiral catalysis over encapsulated chiral complexes. 

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