Effect of La addition on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation
Effect of La addition on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation
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DOI：
10.1016/j.apcata.2007.07.049
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发表时间：
2007-12
影响因子：
5.5
通讯作者：
Yiwei Zhang;Yuming Zhou;Hui Liu;Yu Wang;Yi Xu;Peicheng Wu
中科院分区：
文献类型：
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作者：
Yiwei Zhang;Yuming Zhou;Hui Liu;Yu Wang;Yi Xu;Peicheng Wu
采用连续浸渍法制备了不同La含量的PtSnNaLa/ZSM-5催化剂，并用X射线衍射仪、氮气吸附、NH3-TPD、FT-IR、TPR、H2-TPD、XPS和TPO等技术对催化剂进行了表征。结果表明，La物种在ZSM-5分子筛的内外表面均有较好的分散。少量La的加入使催化剂的酸性略有下降，催化剂的活性中心趋于稳定，从而提高了催化剂的选择性和稳定性。在La含量为1.4%的PtSnNaLa/ZSM-5催化剂上，催化剂的稳定性达到最佳状态，催化选择性最高。丙烷脱氢反应在590℃下反应80h，丙烯的平均产率约为35.2%，但随着La含量的增加，催化剂上铂的活性中心性质发生明显变化，Lewis酸中心数量增多，从而降低了催化剂的活性和选择性。XPS分析结果表明，La的加入抑制了TiN物种的还原。程序升温氧化(TPO)实验表明，适量的La可以有效地防止催化剂结焦，当La含量过多时，则起到相反的作用。
PtSnNaLa/ZSM-5 catalysts with different amounts of lanthanum were prepared by sequential impregnation method, and characterized by XRD, nitrogen adsorption, NH3-TPD, FT-IR, TPR, H2-TPD, XPS and TPO techniques. It was found that the La species were well dispersed on the internal and external surfaces of ZSM-5 zeolite. With a little addition of La, the catalyst acidity decreased slightly and the active sites of the catalyst were stabilized, which resulted in the increased catalytic selectivity and stability. In PtSnNaLa/ZSM-5 catalyst containing 1.4% La, the stability of catalyst reached the best state and the catalytic selectivity was at the maximum. The average yield of propene was about 35.2% over 80h for the reaction of propane dehydrogenation at 590°C. However, as the La content increased, the character of Pt active sites changed obviously and the amount of Lewis acid sites increased, which in consequence decreased the catalytic activity and selectivity. Results from XPS analysis indicated that the addition of La could inhibit the reduction of tin species. Temperature-programmed oxidation (TPO) experiments showed that suitable loading of La could prevent the catalyst from coking effectively, whereas the opposite effect was observed when the content of La was excess.