NOX conversion

A threshold level of oxygen storage (via bulk PdO) is required to reach Ngh CO/NOx conversion levels in dynamometer sweep tests Pd loading, rather than dispersion or surface area, is the most impoirtant factor affecting oxygen uptakes. 

Figure 5.16. Non-thermal plasma-assisted l)cNOx reaction over alumina alone, according to Baudin [32]. GC/MS analysis of outlet gases at 215°C (488 K) and 25% NOx conversion (Figure 5.14b).

Figure 11.13. Model prediction and validation for % NOx conversion as a function of cycle time and lean fraction (red points are the validation points) for 0.5Pt/7.5Ba/2.5Fe 4 catalyst.

This reaction mechanism was suggested by Djega-Mariadassou et al. and several works have been already developed leading to similar results [18,19,20], The maximum of NOx conversion is 50% at 450 °C. 

This reaction is always in competition with the deNOx reaction, limiting the maximum of NOx conversion to N2. It must be pointed out that, during the TPSR tests performed... 

Once more, the beginning of C02 production matches with the first maximum of N02 desorption, suggesting that methane still reacts with N02. Moreover, at 350°C, a second NO high intense peak is observed, due to the NO2-CH4 reaction (in this temperature range, reaction 2 prevails toward reaction 3). From 390°C on, when all N02 is converted, NO reduction to N2 prevails. At 480 °C, the maximum of NOx conversion to N2 is reached (80% of NOx conversion) and, simultaneously, 85% of CH4 is converted to C02 at 500°C. 

The presence of 0.3 wt.% Pd on Co-HFER (3 wt.%) catalyst results on a very important increase of low-temperature interaction of CH4 with N02, as a consequence of both the presence Pd species (Pd2+ and PdO) and the cobalt oxides redistribution (formation of Co oxo-cations and decrease of cobalt oxide). With bimetallic catalyst, under oxygen excess conditions, an increase of 30 % in the NOx conversion to N2 is attained. 

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