화학공학소재연구정보센터
Journal of Catalysis, Vol.172, No.2, 391-405, 1997
The influence of the chromium content on the physicochemical properties and the catalytic behavior of CrOx/TiO2 catalysts for the selective catalytic reduction of nitric oxide by ammonia at relatively high temperatures
Chromia on titania catalysts containing chromium loading ranged from 0 up to 8 mol% Cr have been prepared and calcined at high temperature (500 degrees C). These catalysts have been tested for the selective catalytic reduction of NO by NH3 in excess of O-2 at relatively high reaction temperatures (250-450 degrees C). The physicochemical properties of the prepared samples have been investigated by specific surface area and pore volume measurements, X-ray powder analysis, UV-visible diffuse reflectance spectroscopy, laser-Raman microscopy, X-ray photoelectron spectroscopy, analytical electron microscopy, and temperature programmed reduction experiments. The best catalytic performance has been found for the catalyst containing the lowest amount of active phase (2 mol% Cr). The relatively high catalytic performance of this catalyst has been attributed to the isolated Cr-(vi) surface species strongly interacting with the anatase surface. In fact the physicochemical characterization mentioned above showed that these species are predominant at this low Cr-loading. Increase in the Cr-loading has been found to favor the formation of badly dispersed chromia phases with lower oxidation states. Besides the title reaction, the direct oxidation of NH3 by O-2 and the reaction of NH3 with NO producing N2O take also place at intermediate reaction temperatures (250-350 degrees C). At elevated reaction temperatures (400-450 degrees C) the direct oxidation of NH3 was found to be significant.