Selective catalytic reduction hydrocarbons

Table 10.3. Mechanism proposed for depicting the H2 assisted hydrocarbon selective catalytic reduction of NO over Ag/Al203 (reproduced with permission from Ref. [78])...

At present the most effective available after-treatment techniques for NO, removal under lean conditions are ammonia selective catalytic reduction (SCR) [1-3] and NO, storage reduction (NSR) [4—6]. Indeed, three-way catalysts (TWCs) are not able to reduce NO, in the presence of excess oxygen, because they must be operated at air/ fuel ratios close to the stoichiometric value. Also, non-thermal plasma (NTP) and hydrocarbon-selective catalytic reduction (HC-SCR) are considered, although they are still far from practical applications. 

Thomas, J.F., Lewis, S.A., Bunting, G.B., Storey, J.M., Graves, R.L. and Park, P.W. (2005) Hydrocarbon selective catalytic reduction using a silver-alumina catalyst... 

Supported metal oxides are currently being used in a large number of industrial applications. The oxidation of alkanes is a very interesting field, however, only until recently very little attention has been paid to the oxidation of ethane, the second most abundant paraffin (1). The production of ethylene or acetaldehyde from this feed stock is a challenging option. Vanadium oxide is an important element in the formulation of catalysts for selective cataljdic reactions (e. g. oxidation of o-xylene, 1-3, butadiene, methanol, CO, ammoxidation of hydrocarbons, selective catalytic reduction of NO and the partial oxidation of methane) (2-4). Many of the reactions involving vanadium oxide focus on the selective oxidation of hydrocarbons, and some studies have also examined the oxidation of ethane over vanadium oxide based catalysts (5-7) or reviewed the activity of vanadium oxide for the oxidation of lower alkanes (1). Our work focuses on determining the relevance of the specific oxide support and of the surface vanadia coverage on the nature and activity of the supported vanadia species for the oxidation of ethane. 

The selectivity is dramatically improved, however, if the reductant is ammonia, rather than hydrocarbon. Selective Catalytic Reduction (SCR), using ammonia or a precursor thereof, is a well-established method of NOx abatement. It has been used for thermal power plants in Japan since the 1970s and in Europe since the 1980s. More recently, it has been applied to automotive diesel exhaust to reduce NOx emissions to levels that are presently contemplated. 

Eranen, K., Klingstedt, F., Arve, K. et al. (2004) On the mechanism of the selective catalytic reduction of NO with higher hydrocarbons over a silver/alumina catalyst, J. Catal. 227, 328. 

Shimizu, K Satsuma, A Hattori, T. Selective catalytic reduction of NO by hydrocarbons on Ga203/Al203 catalysts, A/ip/. Catal, B Environmental, 1998, Volume 16, Issue 4, 319-326. 

Iwamoto, M. and Mizimo, N. NOx emission control in oxygen-rich exhaust through selective catalytic reduction by hydrocarbon. Proceedings - IMechE Part D, J. Automobile Eng., 1993, Volume 207, Issue Dl, 23-33. 

The NOx reduction for the exhaust from lean-burn engine is one of the greatest challenges in environmental protection, and a lot of researchers have strived to develop more effective catalysts by many ways. Their efforts could be possibly categorized into four approaches (1) NOx direct decomposition, (2) selective catalytic reduction on NOx with hydrocarbons (HC SCR),... 

For some models adsorption or storage is important. For example, oxygen storage is important in a 3-way catalysis, a catalyst may contain a hydrocarbon storage component for improved low-temperature performance, and ammonia storage is important for ammonia SCR (selective catalytic reduction). Clearly, this sort of behaviour needs to be included in the final model. The nature of the measurements depends on the exact system being studied and will be discussed in more detail later. Suffice to say, from measurements at steady state, the heats of adsorption and coefficients of... 

Destruction of N20 can be carried out at lower temperatures by adding a reductant. In this case an iron-containing zeolite catalyst is used for the selective catalytic reduction of N20 using hydrocarbons as a reductant. The catalyst did not deactivate in a 2000-hour test under demanding conditions (450°C, 6% H20). Hydrocarbons such as propane (or LPG) and methane (widely available as natural gas) can be used as the reducing agent221. 

In the selective catalytic reduction, the hydrocarbon selectively reacts with NOx rather than with O2 to form nitrogen, C02 and water. Traa et al. (54) have classified all the mechanisms proposed in the SCR of NOx by HC over TM-zeolites within three groups ... 

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. 

A great effort is underway to develop reliable aftertreatment systems for lowering NOx emissions from diesel and LB engines. A variety of approaches have been proposed for NOx aftertreatment of advanced vehicles including lean NOx catalysts (LNC), NOx storage and reduction (NSR) catalysts, selective catalytic reduction with urea (urea-SCR), and plasma-assisted catalysis (PAC). Lean NOx catalysts are mainly designed to reduce NOx with unburned hydrocarbons already included in the exhaust stream in the presence of O2 but result in... 

S. Y. Chung, MS Thesis, Selective Catalytic Reduction of Nitrogen Oxides by Hydrocarbons over Dealuminated Zeolite Catalysts, Pohang University of Science and Technology, 1997. 

The selective catalytic reduction (SCR) of nitrogen monoxide by hydrocarbons in excess oxygen currently appears to be the best method for the removal of NO from exhaust streams. This is also a key issue in catalytic purification of diesel exhaust gases, but even more complex due to the presence of SOx. 

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. 

The third strategy for minimizing NOx, known as posttreatment, involves removing NOx from the exhaust gases after the NOx has already been formed in the combustion chamber. Two of the most common methods of posttreatment are selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR).7 Wet techniques for posttreatment include oxidation/absorption, oxidation/absorption/reduc-tion, absorption/oxidation, and absorption/reduction. Dry techniques for posttreatment, besides SCR and SNCR, include activated carbon beds, electron beam radiation, and reaction with hydrocarbons. 

Selective Catalytic Reduction of NOx by Hydrocarbons Over Ag/Al203... 

Eranen, K., Lindfors, L.-E., Niemi, A., Elfving, P. and Cider, L. (2000) Influence of hydrocarbons on the selective catalytic reduction of NOx over Ag/Al2Oj -laboratory and engine tests. SAE paper, 012813. 

Lindfors, L.-E., Eranen, K., Klingstedt, F. and Murzin, D.Yu. (2004) Silver/alumina catalyst for selective catalytic reduction of NOx to N2 by hydrocarbons in diesel powered vehicles. Top. Catal., 28, 185-189. 

Breen, J.P. and Burch, R. (2006) A review of the effect of the addition of hydrogen in the selective catalytic reduction of NOx with hydrocarbons on silver catalysts. Top. Catal, 39, 53-58. 

Sazama, P. and Wichterlova, B. (2005) Selective catalytic reduction of NOx by hydrocarbons enhanced by hydrogen peroxide over silver/alumina catalysts. Chem. Commun, 38, 4810-4811. 

Synthesis and properties of new catalytic systems based on zirconium dioxide and pentasils for process of NOx selective catalytic reduction by hydrocarbons... 

Zirconium dioxide and zeolites of pentasil structure are widely used as catalysts and efficient carriers in many heterogeneous reactions, and particularly in the process of selective catalytic reduction of nitrogen oxides by hydrocarbons (SCR-process) [1,2]. Synthesis of new catalytic systems for NOx SCR-process by CnHm is therefore related with searching for their optimum composition and preparation methods to attain maximum activity in this reaction. 

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