氟改性对不同钨物种在催化剂载体上分散及其加氢脱硫性能的影响

EFFECT OF FLUORINE MODIFICATION ON DISPERSION OF DIFFERENT TUNGSTEN SPECIES ON SUPPORT AND HYDRODESULFURIZATION PERFORMANCE

为了探究改变载体表面结构性质对催化剂的金属物种分散以及加氢脱硫活性的影响,分别将偏钨酸铵和磷钨酸负载在Al2O3和F-Al2O3载体上制备相应的催化剂。XRD、IR、N2吸附-脱附、XPS和TEM等表征结果发现:氟改性可显著降低氧化铝载体表面的羟基数量和载体的等电点;与偏钨酸铵溶液相比,磷钨酸溶液的pH相对较低,更有利于磷钨酸根阴离子在载体表面吸附。氧化态和硫化态催化剂上存在着一些与载体紧密键合、分散较好的钨物种,可抑制Al2O3在水热条件下变成(拟)薄水铝石,但不能避免氟与氧化铝生成氟化铝。采用磷钨酸和氟改性氧化铝匹配制备的催化剂因钨物种能够被较充分地硫化并形成更多片晶较短、层数适中的WS2,从而表现出较高的4,6-二甲基二苯并噻吩加氢脱硫活性。

To study the effect of support surface properties on the dispersion of metal species and hydrodesulfurization performance,ammonium metatungstate and tunstophosphoric acid were loaded on Al 2O 3 and F-Al 2O 3,respectively,to prepare corresponding catalysts.The samples were characterized by XRD,IR,N 2 physisorption,XPS and TEM techniques.The characterization results showed that fluorine modification notably decreased the amounts of hydroxyl groups on alumina support and lowered the isoelectric point of support;compared with that of ammonium metatungstate solution,the pH value of tunstophosphoric acid solution was lower,which favors the adsorption of tunstophosphoric acid anions on the support.On the oxidic or sulfided catalysts,the presence of closely-bonded and well-dispersed tungsten species on support impeded the formation of(pseudo-)boehmite under hydrothermal conditions,but could not avoid the formation of aluminum fluoride by reaction of fluoride and alumina.The catalyst prepared by matching tunstophosphoric acid and F-Al 2O 3 exhibited better HDS activity for 4,6-DMDBT than the other catalysts,due to higher degree of W sulfidation and more shorter WS 2 slabs with proper stacking number.