Study On The Catalytic Properties Of Vanadium-based De-no_x Scr Catalyst At Mid-low Temperature

With the increasing attention to the problem of air pollution,the standard of industrial NOx emission is becoming more and more perfect.In recent years,the denitrification of coking flue gas has been widely concerned.Selective catalytic reduction(SCR)denitrification process is a mature industrial technology.However,the commercial SCR catalysts are difficult to be used in the coking flue gas because of the lower temperature and complicated composition.According to the actual situation of the coking flue gas,this study put forward to modify the conventional SCR catalysts to improve the SCR properties at mid-low temperature.According to the element composition of conventional SCR catalysts,a series of V/Ce-Ti catalysts were prepared using impregnation method with the P25 nano titanium dioxide powder as the catalyst support.The SCR properties and SO2 tolerance of the catalysts at mid-low temperature were investigated.The results indicated that the 4V10Ce-Ti catalyst has the highest denitration efficiency(99 percent at 250?).NH3/NO ratio closer to 1,higher O2 concentration and lower space velocity are beneficial for SCR reaction.The preparation method can affect the efficiency of the catalysts.The study on the SO2 tolerance indicated that SO2 can influence the efficiency of the catalyst to a certain extent.The SO2 tolerance of the 4V-Ti and 4V10Ce-Ti catalysts is better than other V/Ce-Ti catalysts at 250?.Furthermore,the vanadium-based catalysts were modified by some other elements.The results indicated that the addition of Br on the 4V-Ti catalyst can increase the efficiency of the catalyst and the best doping ratio of Br during the preparation is 5 percent.The 4V5Br-Ti catalyst tolerates SO2 well because it can maintain a high efficiency for a long time with SO2 on.The precursor of the doped elements will affect the performance of the catalyst.The presence of Ce reduces the SO2 tolerance of the catalyst at 200 ?,and the presence of SO42-also reduces the SO2 tolerance of the catalyst.XRD and BET test results indicated that the addition of V and Ce doesn't significantly change the crystal type of the catalysts,but slightly reduces the specific surface area and average pore diameter of the catalysts.XPS results indicated that the ammonium hydrogen sulfate is generated on the catalyst surface,and the content of V5+ decreases after adding SO2.The above-mentioned factors contribute to the deactivation of the catalysts.The doping of Br can slow down the formation of sulfate.H2-TPR results indicated that there is interaction between V and Ti02 after loading on the carrier.The redox property of the catalyst is improved with the co-existence of V and Ce.The reaction kinetics of the catalyst were investigated by transient and steady-state experiments.The results indicated that the SCR reaction mechanism of 4V5Br-Ti catalyst is that the adsorbed NH3 reacts with gaseous or weakly surface adsorbed NO.On the test conditions,the reaction order of 4V5Br-Ti catalyst with respect to NH3,O2 and NO is 0,0.5 and 1 respectively.The apparent activation energy of 4V5Br-Ti catalyst is 35.4 kJ-mol"1,which is lower than the apparent activation energy of the current commercial vanadium titanium based catalysts.Through the experimental study and mechanism analysis of this paper,the 4V5Br-Ti catalyst has good SCR properties and SO2 tolerance,and it also has potential practical value.