MgO/HZSM-5中MgO分散状态和催化性能的关系

以硝酸镁、醋酸镁为前身物,通过浸渍法制备了不同系列MgO/ HZSM-5催化剂,用XRD、XPS方法研究了MgO在HZSM-5上的分散状态,用NH3-TPD方法考察了催化剂的酸性,用常压连续流动微型反应装置考察MgO/ HZSM-5在甲苯甲醇烷基化反应中的催化性能.发现前身物不同,MgO在HZSM-5上的分散状态也不同,催化剂的活性和选择性与MgO分散状态密切相关.MgO负载量相同时,在以硝酸镁为前身物制备的催化剂中,MgO在HZSM-5内外表面均有分散,催化剂的对位选择性较高,而活性较低；在以醋酸镁为前身物制备的催化剂中,MgO较多分布在HZSM-5外表面,催化剂的活性较高,但选择性较低.使用醋酸镁为前身物,通过二次浸渍和高温水汽处理,适当改变MgO在分子筛表面的分布并使孔道窄化,可在活性降低较少的情况下显著提高催化剂对二甲苯选择性.

Correlations betwween the Disspersion State OD Mgo and Caralytic Behavior of Mgo/HZSM-5

Two series of MgO /HZSM-5catalysts were prepared by impregnating HZSM-5with solution of Mg (NO 3 ) 2 and Mg (CH 3 COO) 2 .The structures of the samples were c haracterized by XRD and XPS,and the a cidi-ty was determined by NH 3 -TPD.The catalytic behavior of MgO /HZSM-5in the reaction of toluene methylation was investigated on a continuous flo w micro-apparatus under atmospheric pressure.It was found that the disp ersion of MgO was related to the precursor of MgO and had an important effect on the behavior of MgO /HZSM-5cata-lyst.MgO disperses both on the internal surface and on the external surfa ce of HZSM-5in the catalysts prepare d with Mg (NO 3 ) 2 as the precursor of MgO,therefore th e para-selectivity of the catalyst i s higher and the activity is lower.However MgO mainly deposits o n the external surface of HZSM-5in th e catalysts prepared with Mg (CH 3 COO) 2 ,and the activity of catalysts is hig her and the para-selectivity is lowe r.By secondary impregnation and hydrothermal treatment MgO /HZSM-5catalyst with relatively high activity and high para-selectivity wa s ob-tained.