浸液pH值对铂催化剂反应性能和表面性质的影响

本文研究浸液pH值对铂催化剂性能的影响。用烷烃连续流动反应技术以及TPR、XPS、DRS和IR等手段表征催化剂表面性质因强酸处理产生的变化。结果表明:浸液pH值显著影响催化剂的反应性能。随浸液酸度增加,正己烷异构化和芳构化选择性呈线性增大,但却不影响铂的脱氢性能;并且酸度增加导致催化剂酸性(异丙苯裂解活性)下降和高温(>300℃)吸氢中心增加。测试数据也表明,酸处理导致载体表面性质发生了较大变化,氧化态铂物种与载体相互作用增强,部分铂变得较难还原。上述现象归因于在酸性条件下,酸解生成的Al~(3+)离子的再吸附,以及催化剂表面铂簇团短程有序结构的形成和非零价铂的存在。

THE EFFECT OF pH VALUE OF IMPREGNATING SOLUTION ON THE PERFORMANCE AND THE SURFACE STRUCTURE OF SUPPORTED Pt CATALYST

The effect of pH value of impregnating solution on the performance and the surface structure of supported Pt catalyst was studied fwith reactions of hydrocarbons, TPR, XPS, DRS and IR. The results indicated that as the solution acidity increased, the activity for cumene cracking was suppressed, the selectivities of isomerization and aromatization of n-hexane increased linearly, and H_2 uptake at higher temperature went up also, while the activity for cyclohexane dehydrogenation hardly changed. These results showed also that strong acid treatmemt significantly changed the support surface structure, and intensified the interaction between oxidized Pt species and the support, so that part of the Pt became resistant to reduction by H_2.The results above could be attributed to the re-adsorption of Al~(3+) ions from dissolving of A1_2O_3 by the strong acid, and to the fomation of non-zero valent platinum, as well as to the short-range ordered structure in Pt clusters on the surface of the catalyst.