NOX reduction

Chen FI Y and Sachtler W M FI 1998 Activity and durability of Fe/ZSM-5 catalysts for lean burn NOx reduction in the presence of water vapor Catal. Today 42 73-83... 

Figure 3.6.1 (Berty 1979) is a Sankey (1898) diagram, used in power engineering, where the bandwidth is proportional (here qualitatively only) to the flowing masses. This illustrates the calculation results for a rather extreme case of an NOx reduction problem. The case is extreme because the catalyst particle has a dp=0.2mm, i.e., 200 microns. Flow resistance is very high, therefore an L=1 mm deep bend is used only. Per pass concentration drop is still high, Ci-C=1.2ppm, or Dai=0.11. This was tolerated in this case, since it is between 11.2 and 10.00 ppm concentration, and nothing better could have been achieved.

In general, NO and NO2 are mutually beneficial for NOx reduction over the SCR catalysts tested. That is, the presence of NO enhances the NO2 conversion, and vice versa. This results in the synergistic effects of NO and NO2 in the catalytic reduction of NOx with NH3 over CuZSMS, FeZSMS and V20s/Ti02 catalysts. 

One of the most straightforward methods to reduce carbon dioxide emissions is to enhance the fuel efficiency of engines. The three-way catalyst, although very successful at cleaning up automotive exhaust, dictates that engines operate at air-to-fuel ratios of around 14.7 1. Unfortunately, this is not the optimum ratio with respect to fuel efficiency, which is substantially higher under lean-burn conditions at A/F ratios of about 20 1, where the exhaust becomes rich in oxygen and NOx reduction is extremely difficult (Fig. 10.1). 

Kinetic parameters for NOx reduction are summarized in Table 1. It is obvious that the addition of Ir to ln/H-ZSM-5 led to the decrease in reaction orders with respect to NO, CH4, and O2 in the NO-CH4-O2 reaction. The decrease in the order for NO can explain that lr/ln/H-ZSM-5 was effective for the reduction of NO at low concentrations. On the contrary, the reaction orders with respect to NO2, CH4, and O2 in the NO2-CH4-O2 reaction were not significantly changed by the addition of Ir. The retarding effect of CH4... 

Dynamic Behavior of Active Ag Species in NOx Reduction on Ag/Al203 401... 

SCR for heavy-duty vehicles reduces NOx emissions by 80%, HC emissions by 90% and PM emissions by 40% in the EU test cycles, using current diesel fuel (<350 ppm sulphur) [27], Fleet tests with SCR technology show excellent NOx reduction performance for more than 500000 km of truck operation. This experience is based on over 6 000 000 km of accumulated commercial fleet operation [82], The combination of SCR with a pre-oxidation catalyst, a hydrolysis catalyst and an oxidation catalyst enables higher NOx reduction under low-load and low-temperature conditions [83],... 

Figure 6.15. Effect of temperature on stored NOx reduction in H2 (2000 ppm) balance He (total flow 200Ncc/min, catalyst weight 120 mg) over Pt—Ba/Al203 (1/20/100 w/w) catalyst at 200-300-400°C. H2, N2, H20 and NO are outlet concentrations, and H2 is inlet concentration.

Maunula, T., Ahola, J. and Hamada, H. (2000) Reaction Mechanism and Kinetics of NOx Reduction by Propene on CoOx/Alumina Catalysts in Lean Conditions, Appl. Catal. B Environ., 26, 173. 

The NOxTrap can be assimilated to a three-way catalyst7 complemented by a NOz storage function. This system contains two types of precious metals the first one, dedicated to NO, HC and CO oxidation in lean operating mode, will generally consist of platinum or palladium. The second one, dedicated to NOx reduction in rich operating mode, is typically rhodium. Rhodium price spectacularly increases, with a multiplication by three of its value in 2006 (see Figure 7.13)8. 

The OSC materials are able to increase the efficiency by enlarging the operating window of TW catalysts [50,51], NOx reduction in TW catalysts is closely coupled to oxidation reactions since there is a competition between NOx and 02 reaction on the reducers present in the exhaust gases [52], We will first examine the effect of these OSC materials on the oxidation efficiency of TW catalysts. 

Even in absence of the classical Ba component, OSC materials may play a role in the NOx reduction using severely lean/rich conditions. 

Koebel, M., Elsener, M., Krocher, O., et al. (2004) NOx Reduction in the Exhaust of Mobile Heavy-Duty Diesel Engines by Urea-SCR, Topics Catal., 30/31, 43. 

Table 10.2. Summary of the performances of hydrocarbons in NOx reduction over the 1% Pt/Al203 catalyst... 

Presently the catalytic selective NOx reduction by ammonia is efficient and widespread through the world for stationary sources. The remarkable beneficial effect of 02 for the complete reduction of NO into nitrogen is usually observed between 200 and 400°C. However, such a technology is not applicable for mobile sources due to the toxicity of ammonia and vanadium, which composes the active phase in vanadia-titania-based catalysts. Main drawbacks related to storing and handling of ammonia as well as changes in the load composition with subsequent ammonia slip considerably affect the reliability of such a process. On the other hand, the use of urea for heavy-duty vehicles is of interest with the in situ formation of ammonia. 

Denton, P., Giroir-Fendler, A., Schuurman, Y. et al. (2001) A redox pathway for selective NOx reduction stationary and transient experiments performed on a supported Pt catalyst, Appl. Catal. A 220, 141. 

Nova, I., Lietti, L., Castoldi, L. et al. (2006) New insights in the NOx reduction mechanism with H, over Pt-Ba/ y-AFO, lean NO, trap catalysts under near-isothermal conditions, J. Catal. 239, 244. 

Kim, H.H., Takashima, K., Katsura, S. et al. (2001) Low-temperature NOx reduction processes using combined systems of pulsed corona discharge and catalysts, J. Phys. D Appl. Phys. 34, 604-13. 

Rajanikanth, B.S., Srinivasan, A.D. and Ravi, V. (2005) Discharge plasma treatment for NOx reduction from diesel engine exhaust A laboratory investigation, IEEE Trans. Diel. El. Insul. 12, 72-80. 

Kwak, J.H., Szanyi, J. and Peden, C.H.F. (2003) Nonthermal plasma-assisted catalytic NOx reduction over Ba-Y, FAU The effect of catalyst preparation, J. Catal. 220, 291-8. 

Okubo, M., Inoue, M., Kuroki, T. et al. (2005) NOx reduction after treatment system using nitrogen nonthermal plasma desorption, IEEE Trans. Ind. Appl. 41, 891-9. 

Rappe, K.G., Hoard, J.W., Aardahl, C.L. et al. (2004) Combination of low and high temperature catalytic materials to obtain broad temperature coverage for plasma-facilitated NOx reduction, Catal. Today 89, 143-50. 

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