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

Abstract

Ni 2 P/SiO 2 was pretreated with a 0.8% H 2 O–99.2% H 2 flow at 303, 514, and 543 K. The Ni 2 P/SiO 2 catalysts before and after treatment were characterized by N 2 adsorption-desorption, X-ray diffraction, inductively coupled plasma atomic emission spectrometry, H 2 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 Ni 2 P crystallite size, the Ni content, and the Ni/P ratio for the Ni 2 P/SiO 2 catalysts before and after treatment. The treatment at 303 K did not decrease the density of exposed Ni sites on Ni 2 P/SiO 2 , 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 Ni 2 P/SiO 2 . Under the conditions of 513 K, the CB space velocity of 3.75 ml/(g·h), and the H 2 /CB molar ratio of 9.0, the initial CB conversions on the treated Ni 2 P/SiO 2 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 Ni 2 P/SiO 2 may be related to a synergism between the Ni sites and the P-OH groups. 在 303, 514 和 543 K 下用 0.8%H 2 O-99.2%H 2 对 Ni 2 P/SiO 2 催化剂进行了水蒸气处理, 利用 N 2 吸附-脱附、X 射线衍射、电感耦合等离子体发射光谱、H 2 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 Ni 2 P/SiO 2 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, Ni 2 P/SiO 2 催化剂的物相及元素组成、Ni 2 P 晶粒大小、比表面积及孔结构没有明显改变. 与未处理和 303 K 处理的 Ni 2 P/SiO 2 催化剂不同, 513 和 543 K 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 513 K, 氯苯空速 3.75 ml/(g·h) 及 H 2 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 Ni 2 P/SiO 2 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. A promoting effect of steam treatment on the activity of Ni 2 P/SiO 2 for hydrodechlorination of chlorobenzene was found. This is probably related to synergism between Ni sites and P-OH groups.