Abstract:

The role of NbO _x in catalytic combustion of vinyl chloride (VC) was studied by preparing Pt/Nb _x /TiO₂. XRD, XPS, H₂-TPR, NH₃-TPD and Py-FT-IR were used to characterize the effects of NbO _x on the catalyst structure, redox and acidity. The activity results presented that the presence of NbO _x significantly promoted reaction activity of Pt/TiO₂, and the T₉₀ was 246℃ over Pt/Nb_0.09/TiO₂ with the molar ratio of Nb/Ti at 0.09 for vinyl chloride catalytic combustion. Compared with unmodified Pt/TiO₂ catalyst, the value of T₉₀ shifted to lower temperature by 69℃. The existence of NbO _x also affected the total concentration and distribution of chlorinated by-products during VC catalytic combustion. The characterization results illustrated that the introduction of NbO _x further increased the interaction between Pt and support (TiO₂) and the concentration of surface active oxygen species on the catalyst surface which promoted the redox ability of the catalyst. The total acid amount decreased with the increase in NbO _x content, especially the Lewis acid amount. Hence, the total acid amount and acid distribution was not the key factor to affect the activity. The redox property at low temperature played an important role in the increase of activity.

Key words: catalyst, oxidation, catalyst support, vinyl chloride, titania, Pt based catalyst, Nb modification

摘要：

通过制备Pt/Nb _x /TiO₂研究了NbO _x 在催化燃烧氯乙烯中的作用；采用XRD、XPS、H₂-TPR、NH₃-TPD与Py-FT-IR表征了NbO _x 对于催化剂组织结构、氧化还原以及酸碱性的影响。负载NbO _x 可促进Pt/TiO₂反应性能的提高，当Nb/Ti摩尔比为0.09时，即Pt/Nb_0.09/TiO₂可在246℃实现90%氯乙烯的转化；与Pt/TiO₂相比，达到相同转化率的温度向低温偏移69℃。NbO _x 也影响了催化燃烧过程中的含氯副产物的总浓度和分布。催化剂表征结果发现NbO _x 的引入可进一步增加Pt与载体（TiO₂）之间的相互作用，提高催化剂的表面活性氧物种的浓度，进而促进了催化剂氧化还原性能的提高。催化剂表面的总酸量随着NbO _x 含量的增加而降低，尤其是表面Lewis酸量。因此，催化剂表面的酸量和酸分布不是决定反应性能的唯一因素，而低温的氧化还原性更有利于催化剂性能的提高。

关键词: 催化剂, 氧化, 催化剂载体, 氯乙烯, 二氧化钛, Pt基催化剂, Nb改性