DeNOx catalyst

Poisoning of deNOx catalysts by SO2 could also be a problem since diesel fuels contain small amounts of sulfur compounds. Only a few studies deal with this subject [11-13]. It appears from the literature that for Cu catalysts the use of MFI as a support reduces the inhibition by SO2. Support effects also appear in the case of Co since Co/MFI is much less sensitive to SO2 than Co/ferrierite [13]. Since this support effect may be related to acidity, it becomes important, to investigate the influence of SO2 on the properties of Cu catalysts supported on Si02, AI2O3, MFI, BEA and unpromoted or sulfate promot Ti02 and Zr02- These latter have been reported active for deNOx [14]. 

A molecular view of reactions involved over DeNOx catalysts - Mechanisms and kinetics... 

Redox properties of DeNOx catalysts selected samples... 

Figure 5.1. The three-function model for designing DeNOx catalysts in the presence of methane as reductant [12].

Koebel, M. and Elsener, M. (1998) Selective Catalytic Reduction of NO over Commercial DeNOx-Catalysts Comparison of the Measured and Calculated Performance, Ind. Eng. Chem. Res., 37, 327. 

Reductive elimination and storage of dilute NOx has been an important technology to achieve cleaner exhaust gas from engines. At present, Pt, Pd and Rh are often used for the so-called three-way catalyst. The demand for a high-performance DeNOx catalyst with low cost and non-harmful materials is growing as the environmental issues expand worldwide. 

Ti02 support, catalyst, catalyst component major component of DeNOx catalyst... 

HC-SCR DeNOx Catalysts. - Since Held and Konig, Held et and... 

Most of the exhaust gas stream containing NOx from automotive engines includes H2O in the concentration range of 2 to 18% therefore, the strong water tolerance of deNOx catalysts is essential for its commercial application, in addition to their sulfur tolerance in the presence of SOx also contained in the exhaust stream besides NOx. There have been efforts not only to elucidate the effect of H2O on the deNOx efficiency of HC-SCR catalysts, but also to understand the reason why most of the catalysts significantly lose their activity during the deNOx catalysis in wet A few of... 

Hydrothermal Durability of HC-SCR DeNO Catalysts. - Among numerous HC-SCR deNOx catalysts examined, some of the catalysts exhibiting reasonable water tolerance are of particular interest for their commercial use their practical engine applications subsequently require essentially strong hydrothermal stability of the catalyst, particularly zeolite type catalyst. None of the potential SCR catalysts containing appropriate hydrothermal stability for removing NOx from mobile sources have been reported yet. This section will concentrate mainly on the time on-stream stability of potential catalysts for HC-SCR reaction. 

DeNOx reaction involves a strongly adsorbed NH3 species and a gaseous or weakly adsorbed NO species, but differ in their identification of the nature of the adsorbed reactive ammonia (protonated ammonia vs. molecularly coordinated ammonia), of the active sites (Br0nsted vs. Lewis sites) and of the associated reaction intermediates [16,17]. Concerning the mechanism of SO2 oxidation over DeNOxing catalysts, few systematic studies have been reported up to now. Svachula et al. [18] have proposed a redox reaction mechanism based on the assumption of surface vanadyl sulfates as the active sites, in line with the consolidated picture of active sites in commercial sulfuric acid catalysts [19]. Such a mechanism can explain the observed effects of operating conditions, feed composition, and catalyst design parameters on the SO2 SO3 reaction over metal-oxide-based SCR catalysts. 

Figure 10 Typical trend of NO reduction and SO2 oxidation in a honeycomb DeNOx catalyst as a function of the wall thickness, as emerging from calculations in Ref. 38. (Reprinted from Ref. 38, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK. Copyright 1994, all rights reserved.)...

Begsteiger I. (1999) Improved emission control due to a new generation of high-void-fraction SCR-DeNOx catalysts". Catalysis Today, 27, 3-8. 

Lietti L., Forzatti P., Bregani F. (1996) "Steady-State and Trasient Reactivity Study of Ti02-Supported V2O5-WO3 DeNOx Catalysts Relevance of the Vanadium-Tungsten Interaction on the Catalytic Activity . Jnd. Chem. Eng. Res., 35, 3884-3892. 

Matsumoto, S. (1996) DeNOx catalyst for automotive lean-burn engine. Catal. Today, 29, 43-45. 

---