Ce掺杂对钒钨钛催化剂脱硝性能的影响

Effect of Ce doping on denitrification performance of V-W-Ti catalyst

对钒钨钛(V-W-Ti)催化剂进行Ce掺杂制备了Ce_(x)V_(1)W_(7)/Ti(x%为CeO_(2)负载量,以催化剂总质量计,下同),采用XRD、N_(2)吸附-脱附、SEM、XPS、FTIR对其进行了表征,通过NH_(3)/NO-TPD表征了NH_(3)和NO在催化剂表面的吸附强弱分布,并测试了不同CeO_(2)负载量下催化剂的脱硝性能,经密度泛函理论计算探究了催化剂的失活机理。结果表明,CeO_(2)的负载增加了催化剂表面化学吸附氧的比例和Br?nsted酸性位点,减少了催化剂表面V^(4+)的比例和Lewis酸性位点;适当的CeO_(2)负载量能显著提高V-W-Ti催化剂的中低温活性,但负载量过多会降低催化剂的高温活性,CeO_(2)负载量为1%的钒钨钛催化剂(Ce_(1)V_(1)W_(7)/Ti)表现最佳,其在全温度(200~400℃)段的脱硝活性均优于V-W-Ti,在260℃,空速为6×10^(4) h^(–1)的反应条件下,NO_(x)脱除率从79.01%增至99.19%,在含有H_(2)O、SO_(2)的气氛中,其NO_(x)脱除率从58.33%升至74.55%。Ce的掺杂降低了催化剂表面氧空位的形成能,改变了催化剂表面的酸位强弱,强化了SO_(2)在催化剂表面的吸附,SO_(2)中毒后的催化剂表面会沉积硫酸铵盐,在H_(2)O的协同作用下,Ce掺杂后催化剂表面更易沉积硫酸铵盐,这是催化剂失活的主要原因。

Ce_(x)V_(1)W_(7)/Ti(x% refers to the CeO_(2) loading,based on the total mass of catalyst,the same below)was prepared by Ce doping of vanadium,tungsten and titanium(V-W-Ti) catalyst and characterized by XRD,N_(2) adsorption-desorption,SEM,XPS and FTIR.The adsorption strength distribution of NH_(3) and NO on the catalyst surface was characterized by NH_(3)/NO-TPD.The influence of Ce O_(2) loading on the denitrification performance of the catalyst was investigated,while the deactivation mechanism was analyzed by density functional theory calculation.The results showed that the CeO_(2) loading increased the chemisorbed oxygen ratio and Bronsted acid sites,but decreased the V^(4+) ratio on the catalyst surface and Lewis acid sites,on the catalyst surface.Appropriate CeO_(2) loading could significantly improve the activity of V-W-Ti catalyst at low temperature,while excessive loading reduced the catalyst activity at high temperature.The V-W-Ti catalyst containing 1% CeO_(2 )loading(Ce_(1)V_(1)W_(7)/Ti) showed the best performance,with its denitrification activity much better than that of V-W-Ti at all temperatures(200~400 ℃).Under reaction conditions of 260 ℃ and space velocity 6×10^(4) h^(–1),the NO_(x) removal rate increased from 79.01% to 99.19%.In an atmosphere containing H_(2)O and SO_(2),the NOx removal rate increased from 58.33% to 74.55%.Ce doping reduced the oxygen vacancy formation energy on the catalyst surface,changed the strength of the acid site on the catalyst surface,and strengthened the adsorption of SO_(2) on the catalyst surface.Ammonium sulfate was deposited on the catalyst surface after SO_(2) poisoning.Under the synergistic action of H_(2)O,ammonium sulfate was more likely to be deposited on the catalyst surface after Ce doping,which was the main reason for catalyst deactivation.