WO_(3)/TiO_(2)催化剂活性组分W对SO_(2)的氧化特性

Oxidation characteristics of WO_(3)/TiO_(2) catalyst active component W for SO_(2)

采用超声浸渍法制备了不同W负载量的WO_(3)/TiO_(2)催化剂,研究了W负载量、温度及SO_(2)浓度对催化剂表面SO_(2)氧化过程的影响。结果表明,催化剂表面SO_(2)氧化率随W负载量及温度的升高而增大,当W负载量由1%增至7%时,SO_(2)氧化率由0.034%升高至0.210%;而当温度由280℃升高至400℃时,SO_(2)氧化率由0.043%升高至0.240%。通过N_(2)吸附、XRD、Raman、NH_(3)-TPD、H_(2)-TPR及XPS等方法对催化剂样品进行表征。结果表明,活性组分W的增加会导致WO_(x)增加,该结构能够减弱催化剂表面Brønsted酸性位点强度,增强SO_(2)在催化剂表面的吸附,同时导致催化剂表面吸附氧(O_(α))增多,促进SO_(2)氧化;针对W负载量5%的催化剂原位红外试验结果表明,通入SO_(2)后会与催化剂表面W—O—W结构反应形成HSO_(4)^(-),同时将W^(6+)还原为W^(5+)。反应过程中,O_(2)并不直接氧化SO_(2),而是与中间产物反应重新生成W—O—W,使得W^(5+)再次氧化为W^(6+);另外,O_(2)会促进HSO_(4)^(-)向吸附态的SO_(3)转化,促进SO_(3)在催化剂表面的脱附。

A series of WO_(3)/TiO_(2) catalysts with different W loading were prepared by impregnation method,and the effects of W loading,temperature and SO_(2) concentration on the SO_(2) oxidation process on the catalysts were investigated.The results show that the SO_(2) oxidation rate on the catalyst surface increases with the increase of W loading and temperature.The SO_(2) oxidation rate increases from 0.034%to 0.210%when the W loading is increased from 1%to 7%,and the SO_(2) oxidation rate increases from 0.043%to 0.240%when the tempera⁃ture is increased from 280℃to 400℃.N_(2) adsorption,X-ray diffraction(XRD),Raman analysis(Raman),NH_(3) programmed tempera⁃ture(NH_(3)-TPD),H_(2) programmed temperature(H_(2)-TPD),X-ray photoelectron spectroscopy(XPS)were used to characterize catalyst properties.The results illustrate that the increase of W leads to the increase of WO_(x),which can weaken the strength of Brønsted acid site and enhance the adsorption of SO_(2).The oxygen(O_(α))adsorbed on the catalyst increases considerably upon the content of W loading,which is not beneficial to reducing the oxidation of SO_(2).The in-situ FTIR results of 5%W loading show that SO_(2) will react with the W—O—W structure and be oxidized to HSO_(4)^(-),and W^(6+)will be reduced to W^(5+) after the introduction of SO_(2).During the reaction,O_(2) does not directly oxidize SO_(2),but reacts with intermediate products to regenerate W—O—W,which makes W^(5+)oxidized to W^(6+) again.In addi⁃tion,O_(2) promotes the conversion of HSO_(4)^(-) to adsorbed SO_(3),while promoting the desorption of SO_(3) on the catalyst surface.