摘要
采用共浸渍和程序升温还原的方法,在不同的温度下氢气还原4h合成了负载量为30%(以WO3计)的WP/γ-Al2O3催化剂。对合成的催化剂进行了XRD、BET、TG和31P-MAS NMR表征。在3.0MPa和633K的反应条件下,对催化剂的咔唑加氢脱氮(HDN)活性进行了评价。结果表明,当还原温度超过1 023K时活性组分WP在载体表面发生聚集。当催化剂还原温度为923K时,在化学位移为2.4×10-5只能检测到与磷酸盐对应的特征峰;当催化剂还原温度为1 023K和低旋转频率时,在化学位移为2.55×10-4处检测到与活性组分WP对应的特征衍射峰,当高旋转频率时,在化学位移为处6.88×10-4处检测到一个特征峰,该特征峰可能与载体和活性组分之间存在的强相互作用而产生的类似—Al—O—W—P结构的物种有关,这对应与XRD谱图中在40.44°存在的衍射峰。TG结果表明,随还原温度的提高,催化剂前体的磷化程度增加。923K合成的催化剂具有相对最高的咔唑HDN活性,其咔唑HDN转化率达到79%。催化剂咔唑HDN途径有三条:比较低的直接氢解脱氮选择性和比较高的加氢脱氮选择性(一个苯环先饱和然后脱氮,两个苯环饱和然后再脱氮),其中第三条途径,即两个苯环饱和再脱氮为主要途径。
A series of WP/Al2O3 catalysts with WO3 loading of 30% were prepared by impregnation and reduced in H2 for 4 h at different temperatures. The catalysts were characterized by XRD, BET, TG and ^31P MAS-NMR. Over these catalysts, the hydrodenitrogenation （HDN） of carbazole was performed at 633 K and 3.0 MPa. The results indicated that the active species of WP was accumulated on the support surface at a reduction temperature above 1 023 K. Only phosphate was detected at the chemical shift of -2.4 × 10^-5 in the catalyst reduced at 923 K. WP species was observed at the chemical shift of 2.55 × 10^-4 with low speed of sample rotation in the catalyst reduced at 1 073 K, while another peak was also detected with the chemical shift of 6.88 × 10^-4 at high speed of sample rotation; this was probably related to a similar structure of--Al--O--W--P owing to the strong interaction of active species with support, which corresponded to the species with the peak at 20 of 40.44° by XRD. The phosphiding degree of catalyst precursor could be improved by increasing reduction temperature. WP/Al2O3 prepared at 923 K exhibited the highest HDN activity with a carbazole HDN conversion of 79%. Three reaction paths of carbazole HDN were derived, which suggested that hydrodenitrogenation was superior to the direct denitrogenation.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
2008年第2期202-207,共6页
Journal of Fuel Chemistry and Technology
基金
National Basic Research Priorities Program of China (G2000048003)
Beijing Natural Science Foundation (2052009)
Science Technology Program of Beijing Municipal Education Commission(KM200510017003)
关键词
磷化钨
还原温度
咔唑
加氢脱氮
反应选择性
phosphide tungsten
reduction temperature
hydrodenitrogenation
carbazole
reaction selectivity
