Ni_2(OEt)_2/SiO_2催化二氧化碳与丙烯直接合成甲基丙烯酸的研究  

Catalytic Behaviour of Ni_2(OEt)_2/SiO_2 Catalyst for Direct Synthesis of Methacrylic Acid from Carbon Dioxide and Propylene

作　　者：程庆彦[1] 钟顺和[1] 

机构地区：[1]天津大学化工学院一碳化学与化工国家重点实验室,天津300072

出　　处：《催化学报》2003年第7期558-562,共5页

基　　金：国家重大基础研究前期研究专项资助项目 (2 0 0 1CCA0 36 0 0 ) ;国家自然科学基金资助项目 (2 0 0 76 0 35 )

摘　　要：采用表面改性法制备了负载型Ni2 (OEt) 2 /SiO2 双核金属乙氧基配合物催化剂 ,利用示差量热、红外光谱和微反技术对催化剂的表面结构、热稳定性、化学吸附性质和催化活性进行了研究 .结果表明 ,负载型双核金属乙氧基配合物Ni2 (OEt) 2 /SiO2 中的Ni2 + 与载体SiO2 表面的O2 -以双齿配位形式键合 ;二氧化碳在催化剂表面存在桥式吸附态和碳酸单乙酯基物种两种吸附态 ,丙烯则只有一种分子吸附态 ;在适宜的反应条件下 ,二氧化碳和丙烯在Ni2 (OEt) 2 /SiO2 催化剂上的反应产物主要是甲基丙烯酸 .根据实验结果 ,提出了二氧化碳和丙烯在Ni2 (OEt) 2 /SiO2 催化剂表面的反应机理 ,反应物分子共吸附于催化剂表面同一活性单元上 ,羧酸根和丙烯解离吸附态的形成是反应顺利进行的关键步骤 .The supported dinuclear bridged Ni 2(OEt) 2/SiO 2 catalyst for direct synthesis of methacrylic acid from CO 2 and C 3H 6 was prepared by surface modification and ion-exchange method. The surface structure, thermal stability, chemisorption and catalytic performance of the catalyst were investigated by titration method, infrared spectroscopy, differential scanning calorimetry and micro-reactor evaluation techniques. The Ni 2+ bonded with surface O 2- of SiO 2 support in bidentate fashion and the bis-μ-OC 2H 5 bridged structure Ni 2(OEt) 2 formed between the two metal ions. The bridged bis-μ-OC 2H 5 was decomposed at 534 K and 566 K. CO 2 can be chemisorbed on the catalyst in two kinds of states, bridged adsorption state and monoethyl carbonate species. The bridged adsorption state can be transformed into monoethyl carbonate species at higher temperature. C 3H 6 can be chemisorbed on the catalyst only in one kind of state, molecular adsorption state. The influence of reaction temperature, reaction pressure and gas space velocity on the synthesis of methacrylic acid from CO 2 and C 3H 6 was investigated. The Ni 2(OEt) 2/SiO 2 catalyst has higher C 3H 6 conversion and 100% of selectivity for methacrylic acid under appropriate reaction conditions: n(CO 2)/ n(C 3H 6)=2, SV= 1*!500 h -1, p=0.5 MPa, T=443 K. The reaction mechanism for synthesis of methacrylic acid from CO 2 and C 3H 6 on the Ni 2(OEt) 2/SiO 2 catalyst was proposed based on the experimental results. The reactivity is determined by CO 2 and C 3H 6 co-adsorded on the same active center of the catalyst as well as COOH and C 3H 6 in dissociated adsorption state.

关 键 词：二氧化碳 丙烯 甲基丙烯酸 二氧化硅 镍配合物 负载型催化剂 

分 类 号：O643.3[理学—物理化学]