NOX removal

E., and Forzatti, P. (2006) Monolithic catalysts for NOx removal from stationary sources, in Structured Catalysts and Reactors, 2nd edn. Chapter 6 (eds A. Cybulski and J.A. Moulijn), CRC Taylor Francis, Boca Raton, p. 171. 

Previous surface science studies showed that Rh is essential for NOx removal over TWC because NO dissociates more readily on metallic Rh than on Pt and Pd sites [26-28]. Nevertheless, the efficiency of Rh to selectively transform NO into N2 is restricted below the light-off temperature with a predominant formation of N20. Future practical developments are closely related to a better understanding of the formation and on the transformation of N20 over noble metals during the cold start engine. Such an aspect is still challenging over TWC and particularly under lean conditions since the extent in NO conversion is usually significantly lowered. 

Higher concentration of C3H6 and especially higher temperature increase NO removal, but have little effect on NOx removal. 

Another reaction mechanism for NOx removal in the presence of propylene, described in Dorai and Kushner [87] suggests as first step the following reactions of C3H6 with O atoms ... 

Dors et al. [49] investigated NOx removal in a hybrid system consisting in a d.c. corona discharge and a molecular sieve placed inside the plasma region. In the corona discharge, all NO converted was oxidized to N02, so the removal rate of NOx was zero. 

Takaki, K., Shimizu, M., Mukaigawa, S. et al. (2004) Effect of Electrode Shape in Dielectric Barrier Discharge Plasma Reactor for NOx Removal, IEEE Trans. PI. Sci. 32, 32-8. 

Jani, M.A., Takaki, K. and Fujiwara, T. (1999) Streamer polarity dependence of NOx removal by dielectric barrier discharge with a multipoint-to-plane geometry, J. Phys. D Appl. Phys. 32, 2560-7. 

Mok, Y.S., Dors, M. and Mizerazcyk, J. (2004) Effect of reaction temperature on NOx removal and formation of ammonium nitrate in nonthermal plasma process combined with selective catalytic reduction, IEEE Trans. Plasma Sci. 32, 799-807. 

Namihira, T., Tsukamoto, S., Wang, D. (2000) Improvement of NOx removal efficiency using short-width pulsed power, IEEE Trans. PI. Sci. 28, 434-42. 

Dors, M., Mizeraczyk, J. and Nichipor, G.V. (2004) Influence of ammonia on NOx removal in corona discharge-molecular sieve hybrid system,./. Adv. Oxid. Technol. 7, 142-4. 

Dors, M. and Mizeraczyk, J. (2004) NOx removal from a flue gas in a corona discharge-catalyst hybrid system. Catal. Today 89, 127-33. 

Ighigeanu, D., Martin, D., Zissulescu, E. et al. (2005) S02 and NOx removal by electron beam and electrical discharge induced non-thermal plasmas, Vacuum 77, 493-500. 

Orlandini, I. and Riedel, U. Numerical simulation of NOx-removal by pulsed corona discharges - the effect of ethene, AIAA Paper 2000-0720. 

Eichwald, O., Guntoro, N.A., Yousfi, M. et cd. (2002) Chemical kinetics with electrical and gas dynamics modelization for NOx removal in an air corona discharge,./. Phys. D Appl. Phys. 35, 439-50. 

Filimonova, E.A., Kim, Y.H., Hong, S.H. et al. (2002) Multiparametric investigation on NOx removal from simulated diesel exhaust with hydrocarbons by pulsed corona discharge, J. Phys. D Appl. Phys. 35, 2795-807. 

Lee, Y.H., Chung, J.W., Choi, Y.R. et al. (2004) NOx removal characteristics in plasma plus catalyst hybrid process, Plasma Chem. Plasma Process 24, 137-54. 

The typical steps for a gas cleanup system aim at particulate removal, sulfur removal, and NOx removal. This is achieved as follows ... 

SOx and NOx removal Combination of steam/water washing and removing the sulfur compounds for recovery of sulfur as a salable product... 

NSR is very attractive method for NOx removal by storing NOx under lean conditions and then reducing the stored NOx to N2 under rich excursions by engine operation this technology is also referred as a lean NOx trap. In this chapter, NSR catalyst and the mechanism for NOx reduction is described. 

Fig. 32. NOx removal performance of several Zr02-Ti02 catalysts after the sulfur aging test.

Ti02 addition to the NSR catalysts leads to an improvement of SOx resistance of the catalyst. Ti02 is an acidic material, and sulfates on Ti02 are less stable than that on alumina. Fience, Ti02 promotes the decomposition and removal of sulfates in reducing conditions. Also, Zr02 2 mixed oxide as a support for -compounds improves the NOx removal activity. 

These catalysts contained promoters to minimize S02 oxidation. Second-generation systems are based on a combined oxidation catalyst and particulate trap to remove HC and CO, and to alleviate particulate emissions on a continuous basis. The next phase will be the development of advanced catalysts for NOx removal under oxidizing conditions. Low or zero sulfur diesel fuel will be an advantage in overall system development. 

Table 8.5 Photocatalytic activity of several kinds of materials for NOx removal. ([NO], 3.8 ppm relative humidity, 50%)...

Figure 1 shows the non linear dependence of 03 production efficiency on NOx and non methane hydrocarbon (NMHC) levels. The 03 production efficiency is defined as the number of 03 molecules produced per molecule of NOx removed from the atmosphere. This non linear behavior of chemistry in the atmosphere reflects the occurrence of catalytic cycles. It implies the consideration of the spatial variability of short-lived 03 precursors which present important concentration gradients between continental and oceanic areas. 

A key factor in limiting the ozone formation in the atmosphere is the efficiency of NOx removal from the atmosphere. Several reactions participate in the removal in the atmosphere, but in most of the troposphere NOx is removed by the reaction of N02 with OH ... 

Selective Catalytic Reduction. Selective catalytic reduction (SCR) is widely used in Japan and Europe to control NO emissions (1). SCR converts the NO in an oxygen-containing exhaust stream to molecular N2 and H20 using ammonia as the reducing agent in the presence of a catalyst. NOx removals of 90% are achievable. The primary variable is temperature, which depends on catalyst type (38). The principal components of an SCR... 

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