溶胶-凝胶包埋吡啶羧酸钴及其对甲醇氧化羰化反应的催化性能  

Sol-Gel Entrapped Cobalt Pyridine-Carboxylate and Its Catalytic Performance for Oxidative Carbonylation of Methanol

作　　者：李亚玲[1] 赵继全[1] 郑严 葛凤燕[1] 

机构地区：[1]河北工业大学化工学院,天津300130

出　　处：《催化学报》2002年第5期395-399,共5页

基　　金：河北省自然科学基金资助项目 ( 2 0 0 0 0 8)

摘　　要：以正硅酸乙酯为前驱体 ,采用溶胶 凝胶技术将吡啶羧酸钴包埋进SiO2 基体中 ,于 80℃干燥 12h后得到钴含量为2 8% (Co/Si摩尔比 )的干凝胶催化剂 .采用FT IR和TG DTA方法对包埋催化剂进行了表征 ,考察了成胶过程中的pH和水与正硅酸乙酯的摩尔比 (R)对包埋催化剂的结构及其对甲醇氧化羰化制碳酸二甲酯反应催化性能的影响 .结果表明 ,干凝胶催化剂有较高的比表面积 (32 0～ 45 8m2 / g) .在酸性条件下 ,增大 pH或减小R值可缩短成胶时间 .最佳的包埋条件是pH =4,R =6 ,在此条件下制备的凝胶包埋催化剂的活性最高 ,反应 3h ,甲醇转化率为 5 73% ,略低于均相催化剂上的甲醇转化率 .但凝胶包埋催化剂分离简便 ,且重复使用The sol-gel method has advantages over the immobilization procedures employed in the preparation of heterogeneous catalysts. The physical entrapment of homogeneous transition-metal catalysts into silica sol-gel matrices is a simple procedure which makes it possible to convert a variety of soluble metal compounds into recyclable leach-proof catalysts that are more stable than their homogeneous analogues. In this paper, the sol-gel entrapment of cobalt pyridine-carboxylate Co(pic) 2·4H 2O and synthesis of dimethyl carbonate by oxidative carbonylation of methanol were systematically investigated in order to reveal the relation between the preparative conditions and the physico-chemical and catalytic properties of the xerogels. Co(pic) 2·4H 2O was physically entrapped in SiO 2 sol-gel matrices under mild conditions by the sol-gel method using tetraethoxysilane (TEOS) as the precursor. The xerogels were obtained by conventional drying at 80 ℃ for 12 h and then washed with boiling water. The content of cobalt in water was measured by atom absorption spectroscopy and a corporation degree of cobalt in a sol-gel matrix was found to be 2.8% (Co/Si molar ratio).FT-IR and TG-DTA characterization results showed that Co(pic) 2·4H 2O was entrapped in the three-dimensional network of silica and the decomposition temperature of the xerogel is increased by 15 ℃. N 2 adsorption measurement confirmed that the xerogels have high surface areas of 320 to 458 m 2/g. The gelation time was observed to extend with increasing water/TEOS molar ratio (R) or decreasing pH under acid conditions. The xerogel catalyst prepared at R=6 and pH=4 showed the highest activity for the oxidative carbonylation of methanol to dimethyl carbonate. The methanol conversion reached 5.73% after reaction for 3 h, while the conversion over the homogeneous catalyst Co(pic) 2·4H 2O was 6.53%. The xerogel catalyst could be used for 6 reaction cycles without any loss of activity. This suggested that the entrapment of homogeneous metal complex cataly

关 键 词：催化性能 溶胶-凝胶法 包埋 吡啶羧酸钴 干凝胶 甲醇 氧化羰化 碳酸二甲酯 催化剂 

分 类 号：O643.3[理学—物理化学]