甲苯、甲醇苯环烷基化ZSM5沸石催化剂的吸附量热研究  

MICROCALORIMETRIC ADSORPTION STUDY OF ZSM5 ZEOLITE CATALYSTS FOR RING ALKYLATION OF TOLUENE WITH METHANOL

作　　者：王文月[1] 沈俭一[1] 葛欣[1] 

机构地区：[1]南京大学化学系

出　　处：《燃料化学学报》1998年第4期303-306,共4页Journal of Fuel Chemistry and Technology

基　　金：国家自然科学基金

摘　　要：研究了甲苯、甲醇在一系列ＺＳＭ５沸石催化剂上生成二甲苯的烷基化反应。以ＮＨ３为探针分子，用微分吸附量热法表征了这些催化剂的酸性，并与催化活性关联。结果发现，ＨＺＳＭ５沸石上既有强酸位，又有弱酸位，反应产物为热力学平衡组成的二甲苯异构体。浸渍了镁之后，强酸位被中和（对ＭｇＺＳＭ５（２），吸附热位于１３４～８０ｋＪ／ｍｏｌ之间），弱酸位吸附热和样品单位面积上的吸附覆盖度几乎没变。ＭｇＺＳＭ５（２）沸石上的对二甲苯产率为１４．１％，其选择性达到１００％。ＰＺＳＭ５沸石上的弱酸位和大部分强酸位都被中和，对二甲苯的产率较低（６．０％），但选择性也达到１００％。可见，催化剂的强酸性并不有利于甲苯甲醇烷基化反应的高对位选择性。更重要的是中和沸石外表面的强酸位以抑制初级产物在其上进一步发生次级异构化反应。The alkylation of toluene with methanol over several ZSM5 zeolites impregnated with Mg(AcO)_2 and H_3PO_4, respectively, was studied The catalytic reactivities of these catalysts were correlated to their acidities, as determined by microcalorimetric adsorption of NH 3 It was found that HZSM5 possesses some strong acid sites (￣1 15μmol/m 2) corresponding to the adsorption heat of 163￣120kJ/mol and a large amount of weak acid sites with heat around 60kJ/mol, while NaZSM5 only possesses weak acid sites Accordingly, the HZSM5 gives equilibrium composition of xylene isomers, while NaZSM5 shows very low catalytic activity Introduction of magnesium neutralizes the strong acid sites but may not affect acid sites with weaker strength on HZSM5 The conversion of toluene on MgZSM5(2) is about 14 1% with 100% paraselectivity However, introduction of phosphorus may decrease the strength of acid sites at both external surface and internal channels in HZSM5, resulting in the decreased conversion of toluene (6 0%) and increased selectivity to paraxylene (about 100%) It may be concluded that the strong acid sites may not be favorable for the high paraselectivity, and it is more important to neutralize the strong acid sites on the external surface to inhibit the subsequent isomerization of the primary products produced

关 键 词：ZSM-5沸石 催化剂 吸附量热 甲苯 甲醇 烷基化 

分 类 号：O643.36[理学—物理化学]