Vanadium-loaded carbon-based monoliths for the on-board NO reduction: Experimental study of operating conditions

Selective catalytic reduction (SCR) with NH3 and most probably with urea is unanimously regarded as one of the most promising technologies for the abatement of NOx on-board. For this application at low temperatures, carbon-based monolithic catalysts have been prepared using a blend of polymers on cordierite monoliths, doped with two different vanadium compounds and two different loadings (3 and 5%). The active phase precursors were either the ashes of a petroleum coke (PCA) or a commercial NH4VO3. An experimental design was carried out to study the reduction of NO emissions, the selectivity towards N2 and the release of ammonia-slip in the outlet reactor gasses. Both primary measures (temperature, gas space velocity per hour (GSVH) and the molar ratio of NH3/NO) as well as secondary SNR influences were evaluated using a 23 factorial design for the two types of catalysts. Polinomial modellings were deducted from statistical analysis of the experiments, and a good agreement between models and measured data was obtained. The evaluation showed that the temperature is the variable which has a greater influence on all the response variables studied. Spatial velocity shows approximately an equal importance on NO conversion and selectivity towards N2 whereas the molar ratio of NH3/NO is only an important factor in the interaction to other parameters. Catalysts prepared using PCA have similar catalytic behaviour than those prepared with NH4VO3. Although they show a slightly lower catalytic activity, similar selectivity towards N2 and higher values of ammonia-slip.The physical–chemical features of the catalysts, analysed by N2 physisorption, ammonia adsorption and temperature programme desorption have a close relation with the catalysts behaviour. The physical–chemical features are of key importance for achieving a considerable catalytic activity. The values of apparent activation energy calculated for the catalysts presented in this paper were similar to other carbon-based catalysts and smaller than the ones corresponding to TiO2-supported systems.