C_5/C_6烷烃异构化Pt/Al_2O_3-Cl催化剂的性能

Performance of Pt/Al_2O_3-Cl catalysts for C_5/C_6 paraffin isomerization

采用浸渍法制备了Pt/Al2O3,在300℃、CCl4氯化1h,制备出Pt/Al2O3-Cl催化剂。采用FT-IR、XRD、TEM、CO-IR、Py-IR和TPD等方法表征了催化剂,并与中温型RISO催化剂的催化性能进行比较。结果表明,在氯化处理过程中氯取代了氧化铝的表面羟基,导致3000∽3800cm-1红外吸收峰强度大幅度减小,但催化剂的晶相不发生改变;氯化使Pt粒子的平均粒径增大,粒径分布变宽,金属分散度降低;氯化后金属Pt主要以＋2价的Pt Cl2的形式出现,其中一部分生成了易升华的Pt Cl2？2Al Cl3,从而导致Pt含量降低;氯化后的催化剂上只有L酸,评价后既有L酸,又有B酸;氯化后的催化剂热稳定不高,随着温度升高,3种类型的氯化物相继脱出;Pt/Al2O3-Cl相对于中温型RISO催化剂表现出较好的异构化性能,正己烷转化率达88.17%,2,2-二甲基丁烷选择性达29.68%,裂化和氢解几乎没有发生。

Pt/Al2O3 catalyst was prepared by impregnation. The Pt/Al2O3-Cl catalyst was derived from Pt/Al2O3,and chlorided by CCl4 at 300℃ for one hour. The characterization techniques,such as FT-IR,XRD,TEM,CO-IR,Py-IR and TPD,were employed. The performance of Pt/Al2O3-Cl catalyst was compared with that of RISO catalyst. The experimental results show that the OH groups are replaced by chorine in the process of chlorination,leading to a great decrease in the range of high wavenumbers（ 3000 — 3800cm-1）. The structure of alumina does not appear modified upon chlorination. The chlorinated Pt/Al2O3 catalyst exhibits a broad particle size distribution with a larger mean particle size,leading to very low metal dispersion. Simultaneously,platinum is oxidized to platinum chloride,which reacts with Al Cl3 to produce the volatile Pt Cl2？2Al Cl3 complex,so a loss of platinum is observed. Only Lewis acid sites are detected on the fresh catalyst. However,both Lewis and Bronsted acid sites are detected on used catalyst. The chlorinated Pt/Al2O3 catalyst is quite unstable,as shown by continuous release of three kinds of Cl species during TPD measurement. The performance of Pt/Al2O3-Cl catalyst is better than that of RISO catalyst. The n-hexane conversion and 2,2-DMB selectivity are 88.17% and 29.68%,respectively. The hydrogenolysis and hydrocracking of hexane are very limited.