采用超声浸渍法制备了不同W负载量的WO3/TiO2催化剂，研究了W负载量、温度及SO2浓度对催化剂表面SO2氧化过程的影响。结果表明，催化剂表面SO2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，SO2氧化率由0.034%升高至0.210%；而当温度由280 ℃升高至400 ℃时，SO2氧化率由0.043%升高至0.240%。通过N2吸附、XRD、Raman、NH3-TPD、H2-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WOx增加，该结构能够减弱催化剂表面Br-nsted酸性位点强度，增强SO2在催化剂表面的吸附，同时导致催化剂表面吸附氧（Oα）增多，促进SO2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SO2后会与催化剂表面W—O—W结构反应形成HSO-4，同时将W6+还原为W5+。反应过程中，O2并不直接氧化SO2，而是与中间产物反应重新生成W—O—W，使得W5+再次氧化为W6+；另外，O2会促进HSO-4向吸附态的SO3转化，促进SO3在催化剂表面的脱附。

A series of WO3/TiO2 catalysts with different W loading were prepared by impregnation method, and the effects of W loading, temperature and SO2 concentration on the SO2 oxidation process on the catalysts were investigated. The results show that the SO2 oxidation rate on the catalyst surface increases with the increase of W loading and temperature. The SO2 oxidation rate increases from 0.034% to 0.210% when the W loading is increased from 1% to 7%, and the SO2 oxidation rate increases from 0.043% to 0.240% when the temperature is increased from 280 ℃ to 400 ℃. N2 adsorption, X-ray diffraction (XRD), Raman analysis (Raman), NH3 programmed temperature (NH3-TPD), H2 programmed temperature (H2-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 WOx, which can weaken the strength of Brnsted acid site and enhance the adsorption of SO2. The oxygen (Oα) adsorbed on the catalyst increases considerably upon the content of W loading, which is not beneficial to reducing the oxidation of SO2. The in-situ FTIR results of 5% W loading show that SO2 will react with the W—O—W structure and be oxidized to HSO-4, and W6+ will be reduced to W5+ after the introduction of SO2. During the reaction, O2 does not directly oxidize SO2, but reacts with intermediate products to regenerate W—O—W, which makes W5+oxidized to W6+again.In addition, O2 promotes the conversion of HSO-4 to adsorbed SO3, while promoting the desorption of SO3 on the catalyst surface.

0 引言

1 试验材料和方法

   1.1 催化剂制备

   1.2 试验系统与方法

   1.3 表征方法

2 试验结果与讨论

   2.1 WO3/TiO2催化剂上SO3生成特性

   2.2 W负载量对催化剂晶相与孔隙结构的影响

   2.3 W负载量对催化剂表面氧化还原特性影响

   2.4 W负载量对催化剂表面活性组分价态转化影响

   2.5 催化剂表面SO2氧化机理分析

3 结论