Catalysts for selective reduction of NOX

G., and Forzatti, P. (1998) Monolithic catalysts for selective reduction of NOx with NH3 from stationary sources, in Structured Catalysts and Reactors, 1st edn. Chapter 5 (eds A. Cybulski and J.A. Moulijn), Marcel Dekker, New York, p. 121 (b) Nova, 1., Beretta,... 

Table 1 Literature-based representative catalysts for selective reduction of NOx by hydrocarbons... 

Table 2 Literature-based hydrocarbons and related compounds for selective reduction of NOx over SCR catalysts Hydrocarbons...

The replacement of vanadia-based catalysts in the reduction of NOx with ammonia is of interest due to the toxicity of vanadium. Tentative investigations on the use of noble metals in the NO + NH3 reaction have been nicely reviewed by Bosch and Janssen [85], More recently, Seker et al. [86] did not completely succeed on Pt/Al203 with a significant formation of N20 according to the temperature and the water composition. Moreover, 25 ppm S02 has a detrimental effect on the selectivity with selectivity towards the oxidation of NH3 into NO enhanced above 300°C. Supported copper-based catalysts have shown to exhibit excellent activity for NOx abatement. Recently Suarez et al and Blanco et al. [87,88] reported high performances of Cu0/Ni0-Al203 monolithic catalysts with NO/NOz = 1 at low temperature. Different oxidic copper species have been previously identified in those catalytic systems with Cu2+, copper aluminate and CuO species [89], Subsequent additions of Ni2+ in octahedral sites of subsurface layers induce a redistribution of Cu2+ with a surface copper enrichment. Such redistribution... 

The conventional selective reduction of NOx for car passengers still competes but the efficient SCR with ammonia on V205/Ti02 for stationary sources is not available for mobile sources due to the toxicity of vanadium and its lower intrinsic activity than that of noble metals, which may imply higher amount of active phase for compensation. As illustrated in Figure 10.9, such a solution does not seem relevant because a subsequent increase in vanadium enhances the formation of undesirable nitrous oxide at low temperature. Presently, various attempts for the replacement of vanadium did not succeed regarding the complete conversion of NO into N2 at low temperature. Suarez et al. [87] who investigated the reduction of NO with NH3 on CuO-supported monolithic catalysts... 

Burch, R., Fornasiero, P. and Southward, B.W.F. (1999) An investigation into the reactivity, deactivation and in situ regeneration of Pt-based catalysts for the selective reduction of NOx under lean burn conditions, J. Catal. 182, 234. 

Table 3 Water tolerance of Fe-exchanged zeolite catalysts for the selective reduction of NOx by HCs... 

Monolithic Catalysts for the Selective Reduction of NOx with NH3 from Stationary Sources... 

It has been shown by Li and Armor [1,2] that the selective reduction of NOx by methane is produced with high selectivity on zeolitic materials interchanged with Co. Even though the presence of zeolites plays an important role by enabling a high dispersion of Co, its disadvantage is that it is very sensitive to the presence of water vapor. The catalyst systems for the SCR of NOx with methane that will have the greatest impact and... 

It is well known that Cu-HZSM5 zeolites are much better catalysts for the direct decomposition of NO than other catalysts based on different zeolites. However, the lack of large differences in the catalytic performances of the two Cu-loaded zeolites investigated must be related to the specific features of the selective reduction of NOx with hydrocarbons, especially in the real conditions of the engine exhaust gas. Moreover the activity exhibited by the H form of ZSM5 and Y zeolites in the selective reduction of NOx [6, 13] requires the role of the transition metal to be understood, in comparison to that played in the direct decomposition of NO [2, 6,14]. 

SELECTIVE REDUCTION OF NOx WITH AMMONIA OVER CERIUM EXCHANGED ZEOLITE CATALYSTS TOWARDS A SOLUTION FOR AN AMMONIA SLIP PROBLEM... 

Obuchi. A. Kaneko, I. Oi, J. Ohi, A. Ogata. A. Bamwenda, G. R. and Kushiyama, S. A partical sacle evaluation of catalysts for the selective reduction of NOx with organic substances using a diesel exhaust Appl. Catai B Environ., 1998, 75,37-47... 

Griinert W, Hayes NW, Joyner RW, Shpiro ES, Siddiqui MRH, Baeva GN (1994) Structure, Chemistry, and Activity of Cu-ZSM-5 Catalysts for the Selective Reduction of NOx in the Presence of Oxygen. J Phys Chem 98 (42) 10832-10846... 

Ever since the first study of metal-exchanged zeolites as new catalysts for selective catalytic reduction (SCR) of NOx with methane in the presence of oxygen was undertaken (Li and Armor, 1993), the simultaneous catalytic removal of NOx and CH4 at the exhaust of lean-bum natural gas engines has remained a challenge. 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

---