COMPARATIVE ANALYSIS ON MONOLITHIC DENOX CATALYSTS

Abstract

Catalysts based on the Vanadia-Titania system are widely used for the abatement of pollutants, particularly nitrogen oxides (NOx), in the exhaust gases of industrial plants. Their mechanism of operation is based on the catalytic reduction reaction of nitrogen oxides with ammonia (SCR). In this paper, two commercial catalysts based on the V-W-Ti system of very similar nominal composition were compared. The two samples were analyzed in the fresh state and after a period of operation in a waste-gas plant of a waste-to-energy plant. The materials were first characterized from the chemicalstructural point of view through instrumental techniques such as X-ray fluorescence (XRF), X-ray diffractometry (XRD), IR spectroscopy (FT-IR), SEM scanning electron microscopy observations with analysis EDS, measurement of pore size and specific surface area through nitrogen adsorption/ desorption and BET technique. Subsequently, the catalytic properties of the new and used catalysts in the NH3-SCR reaction were evaluated. The results of the analyzes showed that the samples are both made of a titanium matrix in the form of anatase, reinforced with glass fibers, used as a support for the active phases based on V and W. The percentages of vanadium are practically the same for both systems, while the tungsten percentage is very different. The specific surface also has very similar values for the two fresh catalysts. The tests of catalytic activity, on the other hand, have given very different results, particularly for one of the two catalysts, the performance decays much faster than the other. The kinetic measurements show that the decay is not due to a specific surface decrease, due to the presence of precipitates, but to a difference in initial activity between the two catalysts, linked to the different tungsten content.