In this work, ammonia was added to the ion-exchange solution to adjust the pH in the preparation of ion-exchanged CuY by ion-exchange of NaY zeolite with aqueous solution of copper nitrate, and then the ion-exchanged CuY was activated by high temperature calcination. The prepared CuY catalysts exhibited high catalytic activity in the oxidative carbonylation of methanol to dimethyl carbonate. Compared with Cu catalysts prepared by solid-state ion-exchange, precipitation and impregnation, CuY catalysts loaded less Cu and showed good catalytic performance. Based on the characterization of the microstructure of CuY catalysts by XRD, XPS, AES, H2-TPR and elementary analysis, it is shown that by adding ammonia into the ion-exchange solution, the ion-exchanged reaction is promoted, resulting in the increase of the ion-exchanged Cu2+ and the most of Cu2+ in the supercage of CuY catalyst. In the process of calcinating activation of CuY catalysts in inert atmosphere, Cu2+ was auto-reduced to Cu + and ammonia promoted the auto-reduction, which was conducive to the improvement of catalytic activity. The high activating temperature facilitate the auto-reduction progress of Cu2+ to Cu+ located in the supercage of zeolite, Cu+ content in the supercage of zeolite increase more quickly and the catalytic activity of CuY catalysts increase in the meantime. It is concluded that Cu + in the supercage of Y zeolite is the main catalytic active center.%采用硝酸铜溶液和NaY分子筛溶液离子交换制备了CuY催化剂,通过加入氨水提高交换溶液的pH值以及高温焙烧活化,显著提高了该催化剂对甲醇氧化羰基化合成碳酸二甲酯的催化活性,与固相离子交换、沉积和浸渍法制备的催化剂相比,虽然铜的负载量较低,但催化活性较高.通过元素分析、XRD、H2TPR、XPS和Auger电子能谱(Auger electron spectroscopy,AES)等手段对CuY催化剂微观结构的表征结果表明,在Cu(NO3)2离子交换溶液中加入氨水,可促进Cu2+离子交换的进行,提高CuY催化剂的Cu交换量,并且交换的Cu2+主要位于分子筛的超笼中.在惰性气氛中焙烧活化CuY催化剂,Cu2+自还原为Cu+,氨促进了自还原过程的进行,显著提高了催化剂的活性.焙烧活化温度越高,越有利于超笼中Cu2+→Cu+的自还原过程,使超笼中Cu+的含量增加,CuY催化活性增加.进一步的研究结果表明,Y分子筛超笼中的Cu+是主要的催化活性中心.
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