载体硅烷化改性对W/MCM-22催化剂上甲烷脱氢芳构化反应性能的影响

Effect of Silanization on Catalytic Performance of W/MCM-22 for Dehydro-aromatization of Methane

用正硅酸乙脂（TEOS）和三甲基氯硅烷（TMCS）为硅烷化试剂，分别对MCM-22分子筛进行表面改性处理．考察其对所担载W／MCM-22基催化剂上甲烷脱氢芳构化（DHAM）反应性能的影响，结果表明．TEOS或TMCS对MCM-22分子筛载体的硅烷化处理主要导致分子筛外表面最强和最弱的表面酸性位被消去．分子筛孔道内的B酸位（芳构化中心）几不受影响；在DHAM反应化学上表现为：CH4转化率大体持平，但芳烃选择性明显上升，催化剂的结焦／积碳速率有所减缓．单程操作寿命明显延长．在经硅烷化处理的8％W-0．6％Zn／MCM-22催化剂上，苯选择性最高达73．1C％（相应甲烷转化率为15．3％），是未经硅烷化处理相应参比样（61.3C％）的～1．2倍．单程操作寿命从300min延长至470min（就同等芳烃产率水平而言）；类似的结果在Mo促进的W／MCM-22体系上也观察到．经硅烷化改性催化剂上可溶性积炭主要是分子量较低（在200～400范围）的饱和脂肪烃聚合物，而未经硅烷化处理参比样的可溶性积炭分子量多在500以上．

With tetraethyl-orthosilicate （TEOS） and trimethylchlorosilane （TMCS） as silanizing agents, MCM-22 zeolite-support was modified by the silanization using the chemical vapor-treatment or the solution graft method. The effect of silanization of MCM-22 on dehydro-aromatization of CH4 in absence of O2 over W/MCM-22 based catalysts was investigated. The results of the reaction activity assay and the spectroscopic characterization of the catalyst systems indicated that the silanization of MCM-22 zeolite-support led mainly to selective elimination of the strongest and the most weak acidic sites at the external surface of MCM-22, while the Bron- sted acidic sites at the internal surface of the zeolite channel were almost uninfluenced, with the corresponding reaction-chemical behaviors in little change in methane conversion but marked enhancement of the selectivity to aromatic hydrocarbons （benzene and toluene） ,and the alleviation of coke deposltion,as well as the improvement of the durability of the catalyst. Over a silanized 8% W-0.6% Zn/MCM-22 catalyst,73.1 C% selectivity of benzene formation （at 15.3% conversion of CH4 ） could be achieved in the initial 2.5 h of reaction under reaction condition of 0. 1 MPa, 1 073 K,GHSV： 1 500 mL（STP）·h^-1,（g·catal.）^-1 , which was- 1.2 times that （61.3 C% ） of the unsilanized counterpart. The duration of single-pass operation of the catalyst was prolonged to 470 min from the original 300 min, and the CH2Cl2-soluble coke deposits were mainly a series of polymer of saturated aliphatic hydrocarbons with molecular weight in range of 200-400.