KF在CO_2和CH_3OH直接合成DMC负载型金属催化剂中作用的研究

Study on Effects of KF in Supported Metal Catalyst for Direct Synthesis of DMC from Carbon Dioxide and Methanol

用表面改性和离子交换法制备了MgSiO载体,在其中加入KF助剂制备了MgSiO-KF载体,用等体积浸渍法制备了负载型金属铜催化剂.利用IR、化学分析技术,对载体和负载型金属催化剂进行了表征;采用微反技术,考察了催化剂催化CO2与CH3OH反应的性能,并着重研究了KF助剂对催化性能的影响.结果表明,MgSiO中Mg与Si之间形成双齿型配位结构,KF中的F可以取代Mg-Si-O中的桥O形成-Mg-F和K-O-Si结构.CO2在Cu位上形成线式和剪式吸附态,在金属位与Lewis酸活性位Mg2+的协同作用下形成卧式吸附态;CH3OH在催化剂上形成分子吸附态和解离吸附态.在催化剂中引入适量助剂KF,可明显提高催化活性.

MgSiO was prepared by surface modification with ion\|exchange method, MgSiO\|KF were prepared by adding KF auxiliary to surface complex oxide. Supported metal Cu catalysts were prepared by incipient wetness technique. The support and supported metal Cu catalysts were characterized by titration method and IR techniques. Reactivity of CO\-2 with CH\-3OH on catalysts and effects of KF auxiliary on reactivity were characterized by microreactor technique. The research results showed that Mg(Ⅱ) ion bonds with the surface of the SiO\-2 support(of Si-O\+-) in bidentate fashion in the MgSiO, and F can substitute the bridge oxygen of Mg-O-Si to form the structure of -Mg-F and K-O-Si ; Carbon dioxide can chemisorb on the metallic sites to form linear and shearing type, and CO\-2 horizontal adsorption state formed on the metallic sites with the cooperation of supports. Molecular and dissociated methanol adsorption states can be found on the surface of catalysts. Adding KF auxiliary to the supports cannot change the adsorption states of CO\-2 and CH\-3OH, but which can promote the formation of CO\-2 horizontal adsorption state and CH\-3OH dissociative adsorption state. Furthermore, the yield of DMC can be improved by adding KF to the surface complex oxides.