NO Reduction by C3H6 on

The reduction of NO by propene is of great importance in automotive exhaust catalysis. 

As expected, the reaction exhibits pronounced electrochemical promotion behaviour7,25 with a tenfold enhancement in catalytic rate (Fig. 9.17). 

Interestingly as shown in Fig. 9.17 the reaction exhibits pronounced volcano-type behaviour with the rate of N2 production maximized for Uwr=-0.3 V. 

The appearance of volcano type behaviour is perfectly consistent, via Global Rule G3 (Chapter 6), with the kinetic (Fig. 9.18) which show strong competitive adsorption of propene and NO with propene adsorption being stronger on the Na-free surface (Uwr 0 V). Negative Uwr and AO favors the adsorption of electron acceptor NO vs electron donor C3H6 and this is manifest both by the kinetics (Fig. 9.18) and by the observed volcano behaviour (Fig. 9.17). This system is a nice confirmation of Global Rule G3. 

Lambert and coworkers,7 18 25 who were first to study this interesting system, have shown that the nature of the anion (nitrate or carbonate) formed on the catalyst surface in presence ofNa+ plays an important role in the sharpness of the volcano plot obtained upon varying Uwr.- 

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The transition from volcano-type behaviour to electrophobic behaviour upon changing p02 is shown in Fig. 4.31 for the case of CO oxidation on Pt/p -Al203. Another example of volcano-type behaviour is shown in Fig. 4.32 for the case of NO reduction by C3H6 on Pt/ 3"-Al203.98,99... 

C. Pliangos, C. Raptis, T. Badas, and C.G. Vayenas, Electrochemical promotion of NO reduction by C3H6 on Rh/YSZ catalyst-electrodes, Solid State Ionics 136/137, 767-773 (2000). 

Figure 8.61. Transient effect of a constant applied current on the catalytic rates of C02 production, on NO conversion (XN0) and on catalyst potential during NO reduction by C3H6 on Rh/YSZ in presence of gaseous 02.68 Reprinted with permission from Elsevier Science.

Mechanism of NO reduction by Propene We studied the reaction mechanism of NO reduction by C3H6 on Fe-silicate catalyst by means of transient response method in the following manner. First, the reaction was carried out using a mixture of NO, C3H6, and O2 at 573 K (Reaction A). After the N2 formation rate reached the steady-state, the reactant mixture was switched for various components. 

Figure 4.25. Dependence of pco2 and pN2 on the catalyst potential and on the oxygen concentration during NO reduction by C3H6 in presence of 02 on Rh/YSZ.70 Reprinted with permission from Elsevier Science.

Figure 6.4. Examples for the four types of global classical promotion behaviour. Work function increases with the x-axis. (a) Steady-state (low conversion) rates of ethylene oxide (EtO) and C02 production from a mixture of 20 torr of ethylene and 150 torr of 02 for various Cs predosed coverages on Ag(lll) at 563 K19 (b) Rate of water-gas shift reaction over Cu(l 11) as a function of sulphur coverage at 612 K, 26 Torr CO and 10 Torr H202° (c) Effect of sodium loading on NO reduction to N2 by C3H6 on Pd supported on YSZ21 at T=380°C (d) Effect of sodium loading on the rate of NO reduction by CO on Na-promoted 0.5 wt% Rh supported on Ti02(4% W03).22...

Figure 8.62, Effect of temperature on the catalytic rates of C02, N2 and N20 formation and on the corresponding N2 selectivity, for open (unpromoted) and closed (NEMCA) circuit conditions on Rh/YSZ during NO reduction by C3H6.67,68 Reprinted from ref. 68 with permission from Elsevier Science.

Shimizu, K., Kawabata, H., Satsuma, A. and Hattori, T. (1998) Formation and reaction of surface acetate on A1203 during NO reduction by C3H6 Appl. Catal. B Environ., 19, L87-L92. 

The kinetics of NO reduction by C3H6 and by CsHg over Pt/Al203 under lean-bum conditions have been investigated and kinetic models which satisfactorily fit the data have been developed. The state of the Pt surface depends on the relative activities of the reductant and... 

This observation is directly related to the observed dramatic electrochemical promotion of NO reduction by CO and C3H6 in presence of 02 on Rh/YSZ upon electrochemical O2 supply to the Rh catalyst surface (Fig. 2.3 and Chapters 4 and 8). 

Haneda et al. [134,135] studied the formation and reaction of adsorbed species in NO reduction by propene over Ga203-Al203. IR transient reaction technique was employed to examine the reactivity and dynamic behaviour of surface species. The catalyst was first exposed to either C3H6/02/Ar or NO/Oz/Ar at 623 K for a long time to form and accumulate the surface species. The catalyst was further purged with pure Ar and the reaction gas then switched to various gas mixtures. Changes in the intensity of IR bands were measured with time on stream. The main surface species detected by IR during... 

Figure 11. Effect of O2 feed concentration on NO reduction by C3H, over LaCoo gCuo 2O3 [ 19]. Conditions T=450 °C, GHSV=55,000 h , 3000 ppm C3H6, 3000 ppm NO, 0-20,000 ppm O2.

DRIFTS data show the formation of surface NCO" species on catalytic reduction of NO by C3H6 on an Ag-Pd/Al203 surface.467 The IR spectrum of [Ag4Fe2(SCN) 12( 1120)2]2 includes bands from the 32-membered Ag4... 

This paper deals on the influence of the addition of hydrocarbons (C3H6 or C3H8) to CO-NO and CO-NO-O2 mixtures, simulating the composition of the exhaust gas, on the NO reduction by CO performed with different Pd based catalysts. The influence of the addition of CO2 and H2O is briefly mentioned. 

Burch, R. and Watling, T.C. (1998) The effect of sulphur on the reduction of NO by C3H6 and C3H8 over Pt/Al203 under lean-burn conditions, Appl. Catal. B 17, 131. 

Whatever the samples, the NO reduction is strongly inhibited by C3H6 in spite of the reducing character of the reagent mixture. The inhibition is we er with C3Hg than with C3H6 and is mainly observed on Pd/Al203. Such a hydrocarbon inhibition has already mentioned on Pd catalysts by Muraki et al [5]. This effect is clearly explained by carbon deposits whose formation is easier with olefins than with saturated hydrocarbons [10] and an additional treatment with O2 restores the initial activity as shown on table 3. 

Sulfur tolerances of Cu- and H-mordenite zeolite catalysts prepared by ion-exchange were examined in a fixed-bed flow-reactor system. Rates of reduction of NO over HM or CuHM with C2H4 and CuNZA with C3H6 are decreased by SO2 included in the feed gas stream. Surface areas and sulfur contents of the deactivated catalysts, their TGA and TPSR patterns and observations by XPS and Raman suggest the formation of a sulfur species on the catalyst surface in the form of sulfate (SO/ ) which causes the loss of NO removal activity of the catalysts. Data from Cu K-edge absorption spectra suggest sulfur electrostatically interacts with Cu ions on the catalyst surface. 

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