Co掺杂ZnO/MCM-41分子筛的制备及对异戊醇的催化氧化性能

Preparation of ZnO/Co-MCM-41 Molecular Sieves and Their Catalytic Performance for Isoamyl Alcohol Oxidation

以Co掺杂的介孔分子筛MCM-41为载体,采用等体积浸渍法制备了系列5%ZnO/xCo-MCM-41催化剂,并用于催化分子氧氧化异戊醇合成异戊醛的反应.通过X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、紫外-可见漫反射光谱(UV-Vis DRS)、扫描电子显微镜(SEM)、氨气程序升温脱附(NH3-TPD)、氢气程序升温还原(H2-TPR)和氮气吸附-脱附等手段对样品进行表征,并考察了Co掺杂量对分子筛结构和催化性能的影响.结果表明,随着Co掺杂量的增大,样品的比表面积和孔体积均减小,而其平均孔径呈先增大后减小的趋势.当Co掺杂量为0.05时,5%ZnO/0.05Co-MCM-41仍保持了MCM-41高度有序的六方介孔结构,具有高比表面积(989 m2/g)、较大孔径(2.88 nm)和孔体积(0.88 cm3/g),引入的Co主要以孤立态钴离子[Single-site Co(Ⅱ)]形式存在于MCM-41骨架,MCM-41骨架中的Co可以有效提高ZnO微粒的分散度,适度降低5%ZnO/MCM-41的表面酸性,并大幅度提高5%ZnO/MCM-41的氧化还原性.与5%ZnO/MCM-41相比,5%ZnO/0.05Co-MCM-41可使异戊醛的选择性提高28.3%.

Co-doped MCM-41 supported catalysts 5%ZnO/xCo-MCM-41 were prepared by impregnation method, and applied in the synthesis of isovaleric aldehyde from isoamyl alcohol with dioxygen. The samples were characterized via X-ray diffraction（XRD）, fourier transform-infrared spectroscopy（FTIR）, ultraviolet-visible diffuse reflectance spectroscopy （UV-Vis DRS）, scanning electron microscopy（SEM）, NH-3 temperature programmed desorption（NH-3-TPD）, H-2 temperature programmed reduction（H-2-TPR） and N-2 adsorption-desorption. The effects of Co-doping amount on the structure and catalytic performance of molecular sieves were investigated. The results showed that the specific area and pore volume of samples decreased gradually with the increase of Co-doping amount, while median pore diameter first increased and then decreased. 5% ZnO/Co-MCM-41 molecular sieves still remained ordered hexagonal mesopore structure of MCM-41 and had high speci-fic surface area（989 m^2/g）, pore size（2.88 nm） and larger pore volume（0.88 cm3/g） when Co-doping amount was 0.05. The cobalt introduced into Co-MCM-41 existed mainly as single-site Co（Ⅱ） ions, which improved the effective dispersion of ZnO and moderately reduced the acidity of 5% ZnO/MCM-41 mole-cular sieves. At the same time, it improved the oxidation-reduction potential of 5% ZnO/MCM-41. Compared with 5%ZnO/MCM-41, The selectivity of isovaleric aldehyde increased 28.3% with 5% ZnO/0.05Co-MCM-41.