商业V_2O_5-WO_3/TiO_2烟气SCR脱硝催化剂CaSO_4中毒机理研究

基于商业V_2O_5-WO_3/Ti O_2脱硝催化剂,设计了两种模拟Ca SO_4中毒的方法,通过比表面积测定(BET)、X射线衍射(XRD)、程序升温还原(H_2-TPR)、扫描电子显微镜(SEM)、原位漫反射傅里叶变换红外光谱(in situ DRIFTS)等表征技术并结合固定床脱硝性能测试平台,对中毒前后催化剂的微观结构、氧化还原能力及表面性质的变化与脱硝活性进行了对比研究,探索硫酸钙中毒机理。研究表明,Ca SO_4会堵塞催化剂孔径,孔径小于2.7 nm和孔径大于17.8 nm时Ca SO_4的影响更大,从而使催化剂的比表面积和孔体积变小;Ca SO_4中毒会导致Brnsted酸位数量和强度的降低,同时Lewis酸强度也会减弱,从而阻碍了NH_3的吸附,Ca SO_4引起催化剂氧化还原能力的降低。

Mechanism of CaSO4 poisoning commercial V2O5-WO3/TiO2 catalyst for flue gas selective catalytic reduction of NOx with NH3

Based on commercial V₂O₅-WO₃/TiO₂ catalyst,two methods to simulate CaSO₄ poisoning were designed, and the physico-chemical properties of fresh and poisoned catalysts were investigated by BET specific surface area measurement, X-ray diffraction(XRD), H₂ temperature-programmed reduction(H₂-TPR), scanning electron microscope(SEM) and in-situ diffuse reflectance infrared spectrometry (in situ DRIFTS). Meanwhile, the catalytic performance for selective catalytic reduction of NO with NH₃(NH₃-SCR)in a fixed bed was also explored comparatively. SEM results show that CaSO₄ plugs the small hole (pore width smaller than 2.7 nm) and big hole (pore width bigger than 17.8 nm), causing the loss of surface area and pore volume. CaSO₄ could weaken the intensity of both Brnsted acid Sites and Lewis acid sites, particularly the active centers of Brnsted acid sites, which hinders the absorption of NH₃ and reduces the redox abilities.