| Removal of NOX of the flue gas is currently a hot issue in the field of environmental protection at home and abroad. Selective catalytic reduction (SCR) is the most effective and widely used method in NOX desorption of flue gas. Honeycomb V2O5/TiO2catalysts have been running in denitriflcation of industrial flue gas for many years. However, the operating temperature of such catalysts must be above350℃. Long time exposure in high temperature environment could lead to active component sintering on the catalyst surface, resulting in the increase of catalyst particles size and the decrease of surface area, which eventually decrease the catalyst activity. Granular Mn-Ce catalyst has higher denitrification activity in the temperature range of100-400, but the catalyst particles accumulation will lead to the increase of pressure drop in the reactor and dust blocking problems, which is not beneficial to the catalyst application. For the above reasons, the research and development of low-temperature (<200℃) monolithic SCR catalyst has important economic and practical significance. Cordierite honeycomb ceramic used as carrier for catalytic NOX desorption has become a hot topic because of honeycomb catalyst’s low thermal expansion coefficient and resistance to thermal shock. In this paper, cordierite honeycomb ceramic and TiO2are utilized as the support. Monolithic Mn-Ce/TiO2/CC catalysts are prepared by combined sol-gel and impregnation methods. The preparation methods of the TiO2coating were optimized. Synthesis parameters on catalyst and performance of the monolith honeycomb denitration catalyst were studied. Main conclusions of this article are as follows:(1) The relationship between loading rate of titanium coating and the sol aging time, the surfactant, the dipping time, the coating frequency as well as the pretreatment mode of carrier are intimate. The prepared manner of TiO2coating is:ceramic honeycomb were pretreated by25～28%aqueous ammonia for2h, gelation time of titanium sol is72h, using PVA as surfactant, and impregnated at room temperature for30min. The expulsion rate of prepared titanium coating is less than1.5%.(2) Dry titanium sol was calcined for4h at450℃, with the heating rate of1℃/min, then furnace cooling to room temperature. Single crystalline structure of anatase TiO2with uniform particle and smaller particles size can be prepared. These characteristics of titanium coating lay the foundation as catalyst carrier. Titanium coating is flat and smooth in5000magnification. (3) The SCR activity of Mn-Ce/TiO2/CC samples at low temperature is of great difference with the difference of impregnation sequence of active ingredient. NO conversion rate of Mn-Ce/TiO2/CC catalyst which prepared by co-impregnation method is more than80%at100℃and conversion completely when the temperature reach to120℃.(4) The activity of TiO2-coated catalyst is significantly better than the uncoated catalyst. Samples that loaded with12%TiO2coating have the best catalytic effects. NO conversion rate remained at more than90%under the conditions of a space velocity of3000h-2at low temperature (80～180℃). Conversion rate of NO can reach to nearly100%at a reaction temperature of120℃.(5) There are abundant cracks on the surface of Mn-Ce/TiO2/CC catalyst. Main component on the catalyst surface is anatase TiO2. Crystallinity of Mn and Ce was low and active components were highly dispersed on the catalyst surface.(6) Compared with the single manganese catalyst Mn/TiO2/CC, after Ce doping, the specific surface area and pore volume of the catalyst were improved to some extent, and the aperture was correspondingly decreased, which shows that the addition of Ce can reduce the specific surface area loss, pore volume loss and hole collapse of catalyst in the process of calcination. This will be conducive to the full contact of the reaction gas and catalyst surface active sites, thus increase the rate of reaction. |
