WO3增强RuO2/ZrO2表面酸性及其NH3选择性催化氧化性能研究

WO3 enhanced surface acidity of RuO2/ZrO2 and its performance in selective catalytic oxidation of NH3

以氨的选择性催化氧化为主要研究对象,设计制备了RuO2/ZrO2催化剂和一系列不同含量WO3改性的RuO2/ZrO2催化剂。其中,RuO2/ZrO2催化剂显示出优异的催化活性和较差的N2选择性。引入5%或10%的WO3之后RuO2/ZrO2催化剂的活性不变,但是高温N2选择性显著提高,NH3在225℃实现完全转化。然而,当WO3的含量上升至15%和20%时,RuO2/ZrO2催化剂的催化活性稍微有所下降,且相比于RuO2/10%WO3-ZrO2、RuO215%WO3-ZrO2和RuO2/20%WO3-ZrO2催化剂的高温氮气选择性也没有进一步提升,因此,可以判断WO3的最佳含量为10%。此外,通过BET分析发现,WO3的加入能够改变催化剂的微观结构,对应的比表面积随着WO3含量的增加而增大。通过XRD、H2-TPR和XPS表征可知,WO3的引入能够改变ZrO2的晶型结构,使催化剂的稳定性增加,通过原位红外分析可知,WO3的引入使催化剂的表面酸性位点增加,较多的表面酸性位点有利于氨物种的吸附,能够抑制氨与氧气发生快速反应,避免形成较多副产物,是氮气选择性提高的关键所在。

In this paper,RuO2/ZrO2 catalyst and WO3 doped RuO2/WO3-ZrO2 catalysts with different WO3 loadings were designed and prepared for selective catalytic oxidation of ammonia.Among the catalysts,RuO2/ZrO2 catalyst exhibits excellent catalytic activity but poor N2 selectivity.It is worth noting that the activity of RuO2/ZrO2 catalyst remains unchanged after 5%or 10%WO3 doping,while the N2 selectivity at high temperature is significantly improved,and NH3 is completely transformed at 225℃.However,when WO3 content rises to 15%and 20%,the catalytic activity of RuO2/ZrO2 catalyst decreases slightly,while N2 selectivity is not further improved at high temperature.Therefore,it can be judged that the optimal WO3 content is 10%.In addition,it is found that WO3 doping can change the microstructure of the catalyst and the corresponding specific surface area increases with the increase of WO3 content through BET analysis.XRD,H2-TPR and XPS show that WO3 doping can change the crystal structure of ZrO2,increase the stability of the catalyst.According to the DRIFT spectra results,as WO3 is doped into the catalyst,the amount of surface acid sites on the catalyst increase.More surface acid sites can facilitate the adsorption of ammonia species,inhibit the rapid reaction between ammonia and oxygen,and avoid formation of more by-products,which are the key factors to improve the N2 selectivity.