水蒸气处理对Ni_2P/SiO_2催化剂催化氯苯加氢脱氯反应的促进作用

在303,514和543K下用0.8%H2O-99.2%H2对Ni2P/SiO2催化剂进行了水蒸气处理,利用N2吸附-脱附、X射线衍射、电感耦合等离子体发射光谱、H2程序升温脱附及原位漫反射红外光谱等技术对水蒸气处理前后Ni2P/SiO2催化剂的结构进行了表征,并在常压固定床反应器上评价了其催化氯苯加氢脱氯活性.结果表明,经水蒸气处理后,Ni2P/SiO2催化剂的物相及元素组成、Ni2P晶粒大小、比表面积及孔结构没有明显改变.与未处理和303K处理的Ni2P/SiO2催化剂不同,513和543K处理的催化剂表面暴露的Ni中心数量减少,表面P–OH基团数量增多.在513K,氯苯空速3.75ml/(g·h)及H2和氯苯的摩尔比为9.0的反应条件下,经不同温度水蒸气处理的Ni2P/SiO2催化剂上氯苯初始转化率高于93.8%,约是未预处理催化剂的17倍.这可能与金属Ni中心和表面P–OH基团的协同作用有关.

Promotion Effect of Steam Treatment on Activity of Ni2P/SiO2 for Hydrodechlorination of Chlorobenzene

Ni2P/SiO2 was pretreated with a 0.8%H2O-99.2%H2 flow at 303, 514, and 543 K. The Ni2P/SiO2 catalysts before and after treatment were characterized by N2 adsorption-desorption, X-ray diffraction, inductively coupled plasma atomic emission spectrometry, H2 temperature- programmed desorption, and in situ diffuse reflection infrared Fourier transform spectroscopy, and their activities in the hydrodechlorination of chlorobenzene (CB) were tested in a fix-bed reactor. There was no difference in BET specific surface area, pore structure, the Ni2P crystallite size, the Ni content, and the Ni/P ratio for the Ni2P/SiO2 catalysts before and after treatment. The treatment at 303 K did not decrease the density of exposed Ni sites on Ni2P/SiO2, while the treatment at 514 and 543 K led to the decrease of exposed Ni sites and the increase of the P–OH groups on Ni2P/SiO2. Under the conditions of 513 K, the CB space velocity of 3.75 ml/(g·h), and the H2/CB molar ratio of 9.0, the initial CB conversions on the treated Ni2P/SiO2 catalysts exceeded 93.8%, which was much higher than that (5.6%) on the untreated one. The promotion effect of steam treatment on the activity of Ni2P/SiO2 may be related to a synergism between the Ni sites and the P–OH groups.