Preparation And Performance Of V₂O₅-WO₃/TiO₂DeNO_x Catalysts With Low Contents Of Vanadium

Nitrogen oxides (NOx) from coal-fired flue gas and automotive exhaust are the mainpollutants which cause acid rain, photochemical smog and ozone depletion. Selective catalyticreduction (SCR) of NO with NH3has been widely researched due to its advantages of highDeNOxefficiency and low secondary pollution. The molding technology of catalysts has beena hot topic for the significance of catalysts to SCR. At present, the development of moldingtechnology of honeycomb DeNOxcatalysts is more and more mature, but the additivesespecially the porogens, which play an important role in the forming process, are rarelyinvestigated. More and more researchers are interested in seeking a suitable porogen toproduce catalysts with good performance and low cost.The molding technology of V2O5-WO3/TiO2DeNOxcatalysts with low contents ofvanadium was studied. First, the PEO and PMMA microspheres were confirmed as compositepore-forming agents to prepare honeycomb DeNOxcatalysts by the traditional moldingtechnology. It was found the existence of micron-grade pores in the wall of catalysts. Then,the content of other additives was studied which facilitate the molding and surface smoothingof the catalysts:3wt.%methycellulose,7wt.%glass fibers,5wt.%stearic acid and5wt.%lactate. Furthermore, the molding process was optimized on the basis of above, the optimumprocessing technology was: the aging time was24hours; dried process was divided two steps:firstly dried at70℃for12hours, and then completely dried at100℃; calcination conditionwas1℃/min up to500℃and preserved5hours.According to the results of characterization, the honeycomb catalysts possess highmechanical strength as well as large porosity. The effect of pressing pressure and additivecontent of PMMA microspheres to mechanical strength and porosity were evaluated byresponse surface methodology, and the significant regression model showed the significantimpact of the pressing pressure and additive content. The pore size distribution obtained frommercury injection apparatus indicated the existence of nano-micro hierarchical pore.The result of activity test showed that the honeycomb catalyst with pore-forming agentspossessed excellent catalytic activity and N2selectivity. The activity reached90%at250℃and nearly100%during300-450℃. The N2selectivity was enhanced compared with that without pore-forming agents at low temperature. Also, the catalysts showed good SO2/H2Odurability, the catalytic activity maintained at95%after inletting SO2and H2O, and recoveredwhen the SO2and H2O were cut off. The impact of H2O and SO2was reversible, this could beattributed to the competitive adsorption of H2O and SO2with NH3. The NH3slip was only0.2-0.3ppm indicating the absence of ammonia leakage. The SO2/SO3oxygenation efficiencywhich was tested by barium perchlorate-throin method was0.622%. These results proposedthat the catalysts could not be deactivated and avoid the corrosion of equipment. Furthermore,the influence of different routes of W-addition on the catalytic activity was investigated. Theactivity of catalysts prepared by dried H40N10O41W12/TiO2was5%-10%higher than that usingWO3/TiO2.