摘要
采用表面改性法制备了负载型Sn2 (OMe) 4 /SiO2 双核桥联配合物催化剂 ,用IR ,TPD和微反技术对催化剂的表面结构、化学吸附性质和催化活性进行了研究 .结果表明 ,双核桥联Sn2 (OMe) 4 /SiO2 配合物中存在Sn O Si双齿配位形式 ,甲氧基以桥基形式联结两个Sn4+ 离子 ;CO2 在催化剂表面以桥式吸附态和甲氧碳酸酯基吸附态存在 ,而CH3 OH只以分子吸附态存在 .在反应温度 4 13K ,压力 0 5MPa ,反应空速 15 0 0h-1以及CH3 OH与CO2 的摩尔比为 2～ 2 5的反应条件下 ,CO2 和CH3 OH在Sn2 (OMe) 4 /SiO2 催化剂上生成碳酸二甲酯的选择性达到近 10 0 % .根据实验结果 ,提出了CO2 与CH3 OH在Sn2 (OMe) 4 /SiO2 催化剂表面上的反应机理 ,反应物分子共吸附于催化剂表面同一活性位上及CO2 的甲氧碳酸酯基吸附态的形成是反应顺利进行的关键因素 .
Using carbon dioxide and methanol as the raw materials to synthesize dimethyl carbonate (DMC) is an important reaction in the field of synthetic chemistry for carbon resources utilization and environmental protection. In this paper, the supported binuclear bridged Sn-2(OMe)(4)/SiO2 complex for the direct synthesis of DMC from carbon dioxide and methanol was prepared by SiO2 surface modification method and the chemical composition, the surface structure, the thermal stability, the adsorption properties and the catalytic activity of Sn-2(OMe)(4)/SiO2 were thoroughly investigated by titration method, infrared spectroscopy, thermal decomposition spectroscopy, temperature-programmed desorption, and micro-reactor evaluation techniques. The results showed that bis-mu-OMe bridged structure, Sn-2(OMe)(2), can be formed between the two Sn4+ metal ions and be bonded on the surface of SiO2 by Sn-O-Si bonds to form Sn-2 (OMe)(4)/SiO2; CO2 can be chemisorbed on Sn-2(OMe)(4)/SiO2 catalyst to form bridged adsorption state and methoxy carbonate species, the bridged adsorption state can be transformed into methoxy carbonate species at higher temperature; CH3OH can be chemisorbed on the catalyst to form molecular adsorption state; CO2 and CH3OH can react on Sn-2(OMe)(4)/SiO2 catalyst with good reactivity and DMC selectivity, the reaction products were mainly DMC and H2O with few CO, CH4 and CH2O, under a proper reaction condition (temperature 413 K, pressure 0.5 MPa, SV 1500 h(-1) and CH3OH/ CO2 molar ratio 2similar to2.5), the Sn-2 (OMe)(4)/SiO2 catalyst had almost 100% DMC selectivity; the mechanism for DMC direct synthesis from CO2 and CH3OH on the surface of Sn-2(OMe)(4)/SiO2 was proposed based on the experimental results, the reaction of Co-2 and CH3OH co-adsorbed on the same active center on the surface of Sn-2(OMe)(4)/SiO2 and the formation of methoxy carbonate species of CO2 on the surface of the catalyst were the critical steps for the DMC synthesis.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2002年第6期543-548,共6页
基金
国家自然科学基金项目 (2 0 0 760 3 5 )
