【摘要】 采用表面改性和离子交换相结合的方法制备了Ni2 (OCH3 ) 2 /SiO2 负载型双核金属甲氧基配合物催化剂 ,利用红外光谱 (IR)、程序升温脱附 (TPD)、程序升温表面反应 (TPSR)和微反技术考察了催化剂的表面结构以及CO2 和CH3 OH的化学吸附和反应性能 .结果表明 :Ni2 (OCH3 ) 2 /SiO2 中Ni2 + 与载体SiO2 表面O2 -以双齿配位形式键合 ,甲氧基以桥基形式联结双金属离子形成双核物种Ni2 (OCH3 ) 2 ;CO2 在催化剂表面存在甲氧碳酸酯基物种和桥式两种吸附态 ,CH3 OH则只有一种分子吸附态 ;在 10 0～ 2 0 0℃条件下 ,CO2 和CH3 OH在催化剂上的反应产物主要是DMC和H2 O ;根据反应结果 ,讨论了催化反应机理 .更多还原

【Abstract】 The supported dinuclear nickel methoxide complex Ni 2(OCH 3) 2/SiO 2 was prepared by surface reaction modification and ion exchange method. Its chemical composition and surface structure were characterized by element analysis and infrared spectroscopy(IR) techniques. The results showed that, in Ni 2(OCH 3) 2/SiO 2, Ni 2+ bonds with surface O 2- of SiO 2 supported in bidentate fashion and bis μ OCH 3 bridged structure Ni 2(OCH 3) 2 was formed between the two metal ions. The chemisorption properties of CO 2 and CH 3OH on the catalyst were studied by chemisorption infrared spectroscopy and chemisorption temperature programmed desorption(TPD) techniques. The experimental results showed that CO 2 chemisorbs on the catalyst as two states: bridged absorption state and methyl carbonate species. At room temperature, the bridged absorption state is formed between Ni 2+ and OCH 3 ligand , in which metal ions adsorb with the O atom and OCH 3 ligand adsorbs with the carbon atom in CO 2. At higher temperature, it transforms to the methyl carbonate species, the amount of which can be increased by formation of the bridged OCH 3. Whilst CH 3OH only forms molecular adsorption states with O atom in CH 3OH adsorbing on Ni 2+ and desorbs molecularly during 110～140℃, the synergic relationship between Ni 2+ and OCH 3 ligand determines the activation process and the adsorption state of CO 2 and CH 3OH. The catalytic reactivity for Ni 2(OCH 3) 2/SiO 2 was characterized by temperature programmed surface reaction mass spectroscopy(TPSR MS) and micro reactor evaluation techniques. The results revealed that CO 2 and CH 3OH could react on Ni 2(OCH 3) 2/SiO 2 with good reactivity and high DMC selectivity. At 100～200℃, reaction products were mainly DMC and H 2O and the reactivity was determined by surface methoxyl carbonate species and CH 3OH in molecular adsorption states. Based on the results above, the activation processes of CO 2 and CH 3OH and the mechanism for DMC synthesis were analyzed theoretically. The formation and amount of methyl carbonate species of CO 2 on Ni 2(OCH 3) 2/SiO 2 control the procedure of the reaction. The methoxylation of intermediate surface hydroxide is necessary to the catalytic circle.更多还原