NO Reduction by Propene

The selective catalytic reduction of NO by hydrocarbons over metal oxides, such us perovkite-type oxides, has attracted much attention nowadays as promising alternatives to noble metal-supported catalysts. A representative TWC reaction for the NO reduction by hydrocarbons is the NO + CsHe, which is widely investigated in several perovskites (Table 25.5). 

The NO reduction by CsHs was recently studied on a series of La(Co, Mn, Fe)i j,(Cu, Pd)Os perovskites with high surface area and nanozised crystal domains [74,76]. An enhanced performance (100% NO conversion, 77% N2 yield) was achieved at 600 °C over LaFeo.8Cuo.2O3 under a dry feed stream, which was only slightly decreased in the presence of 10% water vapor. In a similar manner, Cu-substituted LaCoi- Cu Os [77] or LaMni, ,CU c03 [78] composites have also shown enhanced performance in this reaction. The better performance of Cu-substituted samples was attributed to the facility in the formation of adsorbed nitrate species via NO oxidation in addition to the intrinsic reactivity of Cu toward NO activation. 

Pd-substituted LaFeo.65Coo.3Pdo.05O3 perovskites were recently examined for NO reduction by propene in the presence of oxygen [80]. For comparison purposes, Pd/LaFeo.65Coo.3503-supported catalysts were investigated. Both composites exhibited remarkable NO conversion at low O2 concentrations, which however is exacerbated upon increasing O2. 

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Figure 4.32. Volcano type behaviour. Effect of Uwr on the rates of C02, N2> N20 formation and on the selectivity to N2 during NO reduction by propene on Pt/p"-Al20j.98,99 Reprinted from ref. 98 with permission from Elsevier Science.

Figure 4.51. Transient effect of a constant applied current on the rates of C02, N2 and N20 production, on NO conversion (XN0) and on catalyst potential (Uwr) during NO reduction by propene in presence of gaseous 02 on Rh/YSZ.70 Reprinted with permission from Elsevier Science.

In the case of NO reduction by propene, the only detectable reaction products were CO2, N2, N2O and H2O. The overall mass balance was found to close within 5% as observed by a combination of GC and mass spectroscopic analyses. Figure 3 shows the effect of varying the catalyst potential on the rate of production of CO2, N2, N2O and on the selectivity towards nitrogen formation, Sn2- As can be seen from this figure, both the CO2 and N2... 

Table 1 Activites for NO Reduction by Propene over Au/AljO, Catalysts. ...

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... 

Sarellas A., Niakolas D., Bourikas K., Vakros J., and Kordulis C. 2006. The influence of the preparation method and the Co loading on the structure and activity of cobalt oxide/y-alumina catalysts for NO reduction by propene. J. Colloid. Interf. Sci. 295 165-72. 

Figure 18. Reversibility of vapor deactivation for LaFeo,8Cuo,203 during NO reduction by propene in the presence of oxygen [81], Conditions 3000 ppmNO, 3000 ppm C3FI6, 1% O2, 0 or 10% H2O, 600 °C, 50,000 h. ...

Haneda, M Kintaichi, Y Hamada, H. Enhanced activity of metal oxide-doped Ga203-AI2O3 for NO reduction by propene, Catal. Today, 1999, Volume 54, Issue 4, 391-400. 

Figure 11 NO reduction by propene with Pt/Na showing promotion of rate and N2 selectivity within a certain window of catalyst potential.

The NO reduction by propene required in general higher reaction temperatures than NO reduction by H2 or CO. NO was totally converted to N2 (100% selectivity) at 260-280°C by all the three catalysts, the 1% Pd/Al203 showing a somewhat higher activity than 1% RU/AI2O3 and 1% Pd-Ru/Al203 catalysts at lower temperatures. 

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. 

Yentekakis, I.V., Konsolakis, M., Lambert, R.M., Macleod, N and Nalbantian, L. (1999) Extraordinarily effective promotion by sodium in emission control catalysis NO reduction by propene over Na-promoted Pt/y-AbOs- Appl. Catal. B, 22, 123-133. 

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