CO偶联反应中氧对Pd-Fe/α-Al_2O_3催化剂活性的影响

Influence of Oxygen on Activity of Pd-Fe/α-Al_2O_3 Catalyst for CO Coupling Reaction to Diethyl Oxalate

在CO常压气相催化偶联合成草酸酯反应体系中 ,考察了原料气CO中不同氧杂质含量和不同反应温度对钯系催化剂活性的影响 .结果表明 ,随着氧含量的增加和反应温度的升高 ,CO的转化率和草酸二乙酯 (DEO)的空时收率升高 ,但DEO的选择性下降 ,且有副产物乙酸乙酯生成 ;氧杂质的存在同时加快了CO偶联主副反应速率 .根据实验现象及XPS表征结果探讨了催化剂活性变化规律的机理 ,并考察了在反应温度下无CO偶联反应时氧对钯系催化剂中活性组分钯及助剂铁的氧化作用 .实验结果表明 。

Since 1980's, the new synthesis technology of diethyl oxalate (DEO) by catalytic coupling reaction of CO in gaseous phase under normal pressure has become an important project of C1 chemical technology in the world, because it is an environmental chemical process. In the industrialization production, there is a little impurity O 2 in the raw gas CO. Therefore, the effect of different contents of O 2 (5%～10%) in the raw gas on the activity of Pd Fe/ α Al 2O 3 catalyst for CO coupling reaction to DEO was experimentally investigated in the range of reaction temperature 105～120 ℃. The surface structure of the Pd containing catalyst was studied by XPS. The experimental results showed that the conversion of CO and the space time yield of DEO increased with increasing O 2 concentration and reaction temperature, but the selectivity for DEO decreased, and a new by product, ethyl acetate, was formed in the reaction system with O 2. The O 2, whose concentration was not more than 10% in the reaction system, could not cause the deactivation of the Pd containing catalyst but accelerated simultaneously the main reaction and the side reaction of CO coupling. The reason for O 2 accelerating CO coupling reaction was discussed on the basis of the experimental phenomena and the XPS measurement results for the catalyst. Oxygen, reacting rapidly with NO product of CO coupling reaction, made the decrease in concentration of the adsorbed NO on the catalyst surface, providing a more efficient space field for CO coupling main reaction and side reaction. The oxidation of the active component Pd and the promoter Fe in the catalyst at the reaction temperature by O 2 without CO coupling reaction was also observed. In addition, it was also found that the activity and selectivity of the catalyst can be fully recovered after removing O 2 from the reaction system.