Selective Catalytic Reduction approaches

When NO destmction efficiencies approaching 90% are required, some form of post-combustion technology appHed downstream of the combustion 2one is needed to reduce the NO formed during the combustion process. Three post-combustion NO control technologies are utilized selective catalytic reduction (SCR) nonselective catalytic reduction (NSCR) and selective noncatalytic reduction (SNCR). 

Selective Catalytic Reduction of Nitrogen Oxides The traditional approach to reducing ambient ozone concentrations has been to reduce VOC emissions, an ozone precurssor. In many areas, it has now been recognized that ehmination of persistent exceedances of the National Ambient Air Qnality Standard for ozone may reqnire more attention to reductions in the other ingredients in ozone formation, nitrogen oxides (NOJ. In such areas, ozone concentrations are controlled by NO rather than VOC emissions. 

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),... 

While the development of flue gas clean-up processes has been progressing for many years, a satisfactory process is not yet available. Lime/limestone wet flue gas desulfurization (FGD) scrubber is the most widely used process in the utility industry at present, owing to the fact that it is the most technically developed and generally the most economically attractive. In spite of this, it is expensive and accounts for about 25-35% of the capital and operating costs of a power plant. Techniques for the post combustion control of nitrogen oxides emissions have not been developed as extensively as those for control of sulfur dioxide emissions. Several approaches have been proposed. Among these, ammonia-based selective catalytic reduction (SCR) has received the most attention. But, SCR may not be suitable for U.S. coal-fired power plants because of reliability concerns and other unresolved technical issues (1). These include uncertain catalyst life, water disposal requirements, and the effects of ammonia by-products on plant components downstream from the reactor. The sensitivity of SCR processes to the cost of NH3 is also the subject of some concern. 

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... 

Selective catalytic reduction (SCR) of NOx employing hydrocarbons (HC s) as reduct ants constitutes a promising catalytic approach in dealing with... 

There is an important number of commercial approaches to NO removal, including adsorptive, thermal and catalytic techniques (Armor 1994, Centi and Forzatti 1995, Fritz and Pitchon 1997). In the case of catalytic processes, the elimination of NO can be carried out by direct catalytic decomposition, or by selective catalytic reduction (SCR) using hydrocarbons or ammonia as reductant. Although several catalytic system have been studied, zeolites have been proposed as interesting catalysts for both reactions. 

In order to decrease the number of bricks in the posttreatment exhaust line, some combinations can be found such as integrating catalytic treatment and filtration step. The aim of this single brick is to reduce the overall size of the posttreatment system and to reduce the cost of the final engine. One approach to achieve this goal is to coat the soot filter with a catalyst composition effective for the conversion of NO in innocuous components. With this selective catalytic reduction filtration (SCRF) concept, the catalyzed soot filter assumes two functions removal of the particulate and conversion of the NO species to N2 of the exhaust stream (Scheme 35.6). 

Biological fuel cells have a long history in the literature,but in recent years, they have come to prominence as more conventional fuel cell technologies have approached mass-market acceptance. Driving the recent ascendance of biofuel cells are the aspects of biocatalysis that are unmatched by conventional low-temperature oxidation—reduction catalysts, namely, activity at near-room temperatures and neutral pH and, more importantly, selective catalytic activity. 

A catalytic, enantioselective approach towards the synthesis of polyol chains has recently been reported by Carreira et al. and has been applied in a synthesis of the polyol subunit of amphotericin B (Scheme 5) [13]. Aldol addition of the silyl dienolate 26 to furfural (27) catalyzed by the Tol-BlNAP-CuF -complex (2 mol-%) gives rise to the addition product 28 in 95 % yield and >99 % ee after one recrystallization. Spectroscopic evidence indicates that a copper dienolate is formed in situ from the silyl dienolate 26 and is actually the active nucleophile [14], Standard transformations including a j-yw-selective reduction of the ft-hydroxy ketone by the method of Prasad and the oxidative conversion of the furan ring to the car-... 

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