Investigation Of Coating Technology And Performance Of Vanadia-molybdena-titania Mixed Oxides Catalyst For NO_x Abatement

With the increasing of atmospheric pollution mainly caused by large amounts of NOx stemming from coal-fired flue gas and motor vehicle exhaust emission, and the gradually improving of people’s environmental protection consciousness recently, the technology of selective catalyst reduction atmospheric NOx with NH3 has being a research focus and been widely applied. Particularly, the honeycomb monolithic extrusive V2O5-WO3/Ti O2 catalyst were the most successful application in the field of industrial flue gas denitration. However, such catalyst cost too much for its large amount of catalyst dosage, and show a decline of its monolithic mechanical strength when molybeenum are added to enhance the resistance of arsenic poisoning of catalyst. Cordierite honeycomb ceramics have been used as substrate material of honeycomb coated catalyst and been widely applied in vehicle tail gas treatment possess for its high mechanical strength and low thermal expansion coefficient. While the characteristics of high hole density, limited coating load and low cohesional strength restrict its application in the field of industry waste gas disposal greatly.Regarding the preparation technology of cordierite honeycomb coated catalyst in this research, dip coating method have been employed to initially coating the nano titania sol that possesses characteristics of high solid content and low viscosity onto monolithic large aperture cordierite substrate material channels, which is then followed by the accretion of Mo and V to the coating of a ready-made catalyst by impregnation. Furthermore, ultrasonic treatment, XRD, UV-vis DRS, Raman and XPS etc characterization methods are used to analyze the influence of technology of catalyst preparation including titania coating and active components dipping time, curing temperature, curing time, impregnation liquid concentration, impregnation technology and ratio of V/Mo etc on loading capacity, adhesive strength, morphology, oxidation-reduction ability and catalytic activity etc.① Washcoating and active components show a fast adsorption rate during the dipping coating process, ca. 0.5h achieve saturation adsorption. Total load of washcoating and active species increase with increase of coating times. 80℃ is the best temperature during the solidification process, ca. 1h load of washcoating and active species tend towards stability.② The layer coated onto the cordierite substrate possesses a homogeneous multilayer distribution with few cracking and peeling on the substrate surface, and strong adherence. Catalyst samples illustrate a type IV nitrogen isotherm with abundant mesopores and little macropores, and stabilized structure which are unable significant influenced by coating process.③ The introduction of molybdenum facilitate to inhibit the growth of VOx crystal and promote partial isolated vanadium diffusing into the lattice of Ti O2, further to generating energy binding of the Ti residual electron shifting to high field and V2 p shifting to low field. The induction of molybdenum causes energy binding of V residual electron shifting to high field and Mo3 d shifting to low field.④ The catalyst samples impregnating molybdenum first reveal a priority to improve the dispersion of active species in the catalyst surface, extend the band gap width of VOx, strengthen its redox ability and increase its catalytic performance at high temperature. Compared with multi-step impregnation, co-impregnation method possess more effective inhibition of vanadium crystallization and promote V to bind with Ti O2. All of the catalyst show a strong resistance to sulfur.⑤ Increase of impregnation concentration gives rise to intensifying the crystallinity of active species and developing more species of amorphous active species, reducing the performance of catalyst at high temperature for the reinforced oxidizability while enhancing its low temperature performance. The interactions between supporter and active species decline, energy binding of V2 p, Mo3 d and Ti2 p shift to low field.⑥ Increase of Mo/V ratio restrict the grain growth of VOx and anatase titania, promote the dispersion effect of molybdenum on vanadium and improve its catalyst performance.