SiO2@ZIF-67核殼微球應用於二氧化碳環加成反應

Abstract

本研究利用多次重複合成反應成功將有機金屬骨架ZIF-67生長於二氧化矽球形模板上，形成SiO2@ZIF-67核殼材料，藉由改變核殼材料之尺寸大小、添加不同金屬離子或碳化材料等三種方法，探討對於二氧化碳環加成反應之催化活性影響。第一部分探討不同尺寸大小之球型二氧化矽，分別選用直徑大小為1、2、5與10 μm之二氧化矽作為模板，探討在不同尺寸模板下對於MOF含量的影響及二氧化碳耦和反應之差異。由實驗結果得知，直徑1 μm之核殼材料具有最高的活性，與其他催化劑相比可高出一倍的活性，其TOF值達到52 h-1。第二及第三部分為優化催化劑之催化效能。第二部分中，將Cu2+及Fe2+分別於合成過程中摻入，成功在不改變ZIF-67晶相結構，於二氧化矽表面形成雙金屬MOF(SiO2@M-ZIF-67, M = Cu or Fe)，使其同時具有兩種金屬，即為兩種活性位點。在催化反應的結果中，與SiO2@Cu-ZIF-67相比，SiO2@Fe-ZIF-67擁有較高的轉換率為88%。第三部分則是將製備好的SiO2@ZIF-67進行400、500及600 ℃的高溫鍛燒，形成SiO2@quasi-ZIF-67。鍛燒過後，二氧化矽表面的ZIF-67由於熱處理導致金屬及ligand的斷鍵，PXRD的結果表明其與原先的晶體結構完全不同，其中以500 ℃熱處理的SiO2@quasi-ZIF-67-500 ℃在催化實驗中，具有轉換率71%，其TON值高達249 h-1，為原先的六倍之多。關鍵字 : 金屬有機骨架、核殼微球、環加成反應、催化劑、碳化、雙金屬有機骨架

In this study, the metal-organic frameworks ZIF-67 was successfully grown on the silica spherical template to form SiO2@ZIF-67 core-shell material by using multiple synthesis reactions. The catalytic activity of the core-shell material for epoxidation addition reaction was also optimized by changing the synthesis conditions of the core-shell material.In the first part, the different sizes of spherical silica were investigated, and silica with diameters of 1, 2, 5 and 10 μm were chosen as templates to investigate the effect on the MOF content and the difference of CO2 coupling reaction under different sizes of templates. From the experimental results, the core-shell material with a diameter of 1 μm has the highest activity, which can double the activity TOF value up to 52 h-1 compared with other catalysts.The second and third parts are to optimize the catalytic efficiency of the catalysts. In the second part, Cu2+ and Fe2+ were incorporated in the synthesis process to form a bimetallic MOF (SiO2@M-ZIF-67, M=Cu, Fe) onthe silica surface without changing the crystalline structure of ZIF-67. From the experimental results, SiO2@Fe-ZIF-67 has the higher conversion rate of 88 % in the cycloaddition reactionIn the last part, the SiO2@quasi-ZIF-67 was further treated under different carbonization temperatures ranging from 400oC to 600oC. Then, the SiO2@quasi-ZIF-67 was also taken as catalyst for the cycloaddition reaction of carbon dioxide and propylene oxide. The composite SiO2@quasi-ZIF-67-500 °C showed conversion rate of 71 %, has the highest TOF value up to 249 h-1.Keywords : core-shell microspheres, metal–organic framework, cycloaddition reaction, catalysts, carbonization, bimetallic MOF