两种Keggin型有机-无机混配物的结构及催化消除甲醇的研究

Crystal structure of the two new inorganicorganic hybrid polyoxometalate and catalytic elimination of gaseous methanol

为了寻找高效消除挥发性有机污染物的新材料,克服单纯杂多酸催化剂催化性能低、稳定性差的缺点,采用水热法合成了两种新的具有Keggin型杂多酸骨架的有机-无机混配配合物单晶,分别为(4-C6H7N)2(4-C6H8N)3PW12O40·H2O(配合物1)和(4-C5H7N2)3(PW12O40)·5H2O(配合物2),用X-射线单晶衍射、红外光谱、紫外光谱、差热-热重进行了表征。配合物1和2由1个Keggin型PW12O40阴离子与有机配体4-甲基吡啶或4-氨基吡啶组成,并通过广泛的氢键作用在空间上无限延展形成超分子网络结构。配合物1为单斜晶系,晶胞参数为:a=16.0569(10),b=19.8781(17),c=18.4728(15),α=90.00°,β=98.384(7)°,γ=90.00°。配合物2为单斜晶系,晶胞参数为:a=11.8880(9),b=20.0148(15),c=25.495(2),α=90.00°,β=96.279(5)°,γ=90.00°。在流动催化反应体系中,探讨了该两种配合物催化消除甲醇的能力。体系流速为10 m L/min,甲醇初始质量浓度为3.0 g/m3,配合物1在150℃时对甲醇的消除率达到85.25%,配合物2在140℃对甲醇的消除率达到53.00%。

This paper is aimed at introducing two kinds of new organic-inorganic hybrids,which can be used as the catalysts for catalytic elimination of the gaseous methanol. The two hybrids are synthesized by hydrothermal method and characterized by singlecrystal X-ray diffraction,IR,UV- Vis and TG- DTA. The socalled compound 1 and compound 2 are made from Keggin polyoxoanions and 4-methylpyridine or 4-aminopyridine organic ligands,which tend to display an extended three-dimensional supramolecular network via the hydrogen bonding. In addition,both compound 1 and compound 2 have been crystallized in the monoclinic system. The TG- DTA curves show that they both enjoy high thermal stability with the decomposition temperature over 300 ℃,which helps to provide a theoretical basis for the catalytic testing and measurement of the temperature. We have also managed to use the catalytic elimination of methanol as a model reaction to evaluate the catalytic performance of the two compounds. In proceeding with our research,we have also conducted a catalytic reaction with a continuous-flow fixed-bed micro-reactor,with the reaction temperature being arranged in a range from the room temperature to 200 ℃. We have also been trying to adopt the elimination rate of methanol to evaluate the catalytic activity of the compounds,finding that,as the reaction temperature increases,the elimination rate of methanol tends to rise first and then drop on the condition that the concentration of the reactants keeps constant. When the initial concentration of the methanol is about 3g / m3 in the air and the flow velocity is 10 m L / min,it is possible for the methanol elimination rate to reach 85. 25% at 150 ℃ over compounds 1 and 53. 00% at 140 ℃ over compounds 2. As compared with the pure Keggin-type tungstophosphoric acid,both the catalytic activity and stability of the two compounds can be improved for they are by nature a mesh supra-molecular structure whereas the structure of the tungstophosphoric anion has been stabilized and the organic molecules of the 4-picoline are a 4-aminopyridine enhanced affinity and adsorbability to organic pollutants,which plays an important role in catalytic reaction,so has the catalytic activity increased.