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

Abstract

Abstract Selective catalytic reduction (SCR) with NH 3 and most probably with urea is unanimously regarded as one of the most promising technologies for the abatement of NO x 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 NH 4 VO 3 . An experimental design was carried out to study the reduction of NO emissions, the selectivity towards N 2 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 NH 3 /NO) as well as secondary SNR influences were evaluated using a 2 3 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 N 2 whereas the molar ratio of NH 3 /NO is only an important factor in the interaction to other parameters. Catalysts prepared using PCA have similar catalytic behaviour than those prepared with NH 4 VO 3 . Although they show a slightly lower catalytic activity, similar selectivity towards N 2 and higher values of ammonia-slip. The physical–chemical features of the catalysts, analysed by N 2 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 TiO 2 -supported systems.