氯化条件对正己烷异构化Pt/Al2O3催化剂性能的影响

采用浸渍法制备了Pt/Al2O3催化剂,在250和300℃下氯化不同时间,得到两个系列的Pt/Al2O3 Cl催化剂。采用BET、NH3 TPD、Py IR等方法表征了制备的催化剂。以正己烷为原料,在反应温度140℃、压力20 MPa、体积空速12 h-1、氢/油摩尔比2的条件下,考察了Pt/Al2O3 Cl催化剂的异构化催化活性和异构产物选择性。结果表明,在相同温度下,氯化时间越长,Pt/Al2O3 Cl的比表面积越小,孔径越大。在250℃氯化时,氯化时间越长,催化剂酸量和氯质量分数越高,催化正己烷异构化活性和异构产物选择性越高;但在300℃氯化时,氯化时间超过1 h,所得Pt/Al2O3 Cl的酸量和氯质量分数下降,催化性能变差。氯化后的Pt/Al2O3 Cl催化剂只有L酸位,经异构化反应评价后催化剂既有L酸又有B酸。300℃氯化1 h最佳,所得Pt/Al2O3 Cl催化正己烷异构化的转化率为8405%,2〖DK〗,2 二甲基丁烷选择性为2654%;连续运行300 h,催化剂活性几乎不改变。

Effect of Chlorination Treatment on Performance of Pt/Al2O3 Catalysts for n-Hexane Isomerization

Pt/Al2O3 catalysts were prepared by impregnation. Two series of Pt/Al2O3 Cl catalysts were obtained from Pt/Al2O3 chloridized at 250℃ and 300℃ for different time, and characterized by BET, NH3 TPD, Py IR techniques. The catalytic activity of Pt/Al2O3 Cl was evaluated by n hexane isomerization under a space velocity of 12 h-1, 140℃, 20 MPa and hydrogen and hexane molar ratio of 2. The results revealed that at the same temperature the longer the chlorination time, the smaller the specific surface area and the larger the pore size of Pt/Al2O3 Cl. The Cl mass fraction, isomerization activity and acid amount of Pt/Al2O3 Cl increased with the increase of chlorination time at 250℃, but decreased as chloridized at 300℃ for more than 1 h. Only Lewis acid sites were detected on fresh Pt/Al2O3 Cl, however, both Lewis and Brnsted acid sites were detected on used one. The catalytic performance of Pt/Al2O3 Cl chloridized at 300℃ for 1 h was the best for n hexane isomerization, with the conversion and 2〖DK〗,2 DMB selectivity were 8405% and 2654%, respectively, and good stability for 300 h continuous operation without any decline.