负载型双核配合物Cu_2(μ-iOPr)_2/SiO_2的制备与表征及其超临界条件下合成DMC的反应性能

Preparation and Characterization of Cu_2(μ-iOPr)_2/SiO_2 Catalyst and its Reactivity for DMC Synthesis under Supercritical Condition

采用表面改性和离子交换相结合的方法制备了 SiO2 负载的 Cu2(μ-iOPr)2 双核配合物催化剂,用化学分析、IR、TPD-MS 和超临界反应技术考察了催化剂的表面构造及 CO2 和 CH3OH 在催化剂上的化学吸附和超临界条件下的反应性能。结果表明:负载型双核配合物 Cu2(μ-iOPr)2/SiO2中金属离子 Cu2+与载体 SiO2表面 O2-以双齿配位键合,配体以桥基形式连接双金属离子形成双核物种 Cu2(μ-iOPr)2;CO2在催化剂表面存在桥式和异丙氧碳酸酯基两种吸附态,其中异丙氧碳酸酯基吸附态是生成 DMC 的关键物种;CH3OH 在催化剂上只有一种分子吸附态。在适宜的超临界条件(温度 130℃,压力 7.5MPa,催化剂/甲醇=0.05(质量比))下,DMC 的选择性为 100%,甲醇的转化率可达 5%左右。

SiO2 supported binuclear complex, Cu2(μ-OPr)2/SiO2 catalyst was prepared by surface modification and ion-exchange method. Surface structure of the catalyst, chemisorptions and reaction properties of CO2 and CH3OH under supercritical conditions on this catalyst were studied by chemical analysis, IR, TPD-MS and supercritical techniques. The experimental results show that, in the Cu2(μ-iOPr)2/SiO2, copper (II) bonds with the surface O2- of the SiO2 supporter (of Si-O-) in bidentate fashion and bis-μ-iOPr bridged structure Cu2(μ-iOPr)2 is formed between two Cu(II) ions, that CO2 can be chemisorbed on the catalyst as two states: the bridged absorption state or isopropoxy carbonate species, the later is the critical species for DMC synthesis, and the adsorption of CH3OH on the catalyst has molecular adsorption state only. Under proper supercritical condition (reaction temperature 403 K, pressure 7.5 MPa, and catalyst/methanol=0.05 (mass ratio)) XCH3OH is about 5% and the selectivity of DMC reaches 100% when the above catalyst is used.