Study On Preparation And Properties Of Vanadia-base Catalysts Of Reducing NO

Selective Catalytic Reduction of NO has attracted much attention and significant effort has been made to enhance the properties of existing catalysts. However, the synthesis of catalyst with high efficiency still remains one of the difficult tasks. Especially, in the synthesis of novel catalyst, only a limited success has been achieved to enhance the properties and selective efficiency.The current work presents the modification effect of silica sol modified cordierite carrier, and optimal process was obtained. The results showed that the BET surface area of resulting carrier was largely increased from 0.92 m²/g to 46.47 m²/g, and the surface area of resulting carrier was significantly enhanced by the addition of Pore-Expanding Agent (Hexamethylenetetramine, HMTM) and the using of Microwave Heating Method. The BET surface area of resulting carrier was further increased to 72.13 m²/g under optimized experimental conditions that the coating solution was prepared by mixing of one-quarter volume of HMTM solution (3M) and three quarters of silica sol. Carrier was immersed under microwave, followed by drying at 110℃and calcination at 400℃.Vanadia-base Catalysts were prepared by the loading of Vanadium, Tungsten and Molybdenum Oxides on the surface of modified carriers, and the effects of reaction conditions and component on the abilities of reducing NO into N₂ were investigated in home-made reactor wherein NO and N₂ were used as the gas model and Urea were treated as reductant. Based on the experiments, 79.68% NO conversion efficiency can be achieved in our experiment during temperature between 350-400℃. The conversion rate of NO was higher when the reaction decreased as the increment of space velocity. The optimal activity of the catalyst was found when the flow rate of Urea was set to 0.3 mL/L which is near the excellent ammonia to nitrogen ratio. The activity of catalyst increased when the loading of Vanadium Oxide increased and the desirable loaded amount was 2 wt%. BET results indicated V-W-O/SiO₂/CC displayed largest pore diameter which has the advantages of speeded inner diffusion and increased diffusion rate to cause an increasement of molecule into pore and finally improved the performance of the catalyst. XRD and energy sperctrum results reveal that the introduction of Tungsten Oxide significantly increased the uniformity as well as the loading of Vanadium Oxide on the surface of modified cordierite, which finally enhanced the activity of the catalyst. However, the reduced reactivity was observed when the second addition of Molybdenum Oxide. This is attributed to the active centre (Vanadium Oxide) was completely covered or entrapped by the Molybdenum Oxide, resulting in the isolation from reaction gases. XPS experiment also indicate that Vanadium Oxide could be easily formed when Vanadium was loaded on the surface of SiO₂..