Preparation Of Microporous Membrane Coated Pd/Al₂O₃ Core-shell Catalyst And Its Catalytic Performances

Core-shell catalyst encapsulated with microporous membrane exhibits many special characteristics. For example, it can control the products distribution and enhance selectivity for desired products; meanwhile,the microporous membrane is a great help to minimize probability of deactivation of active sites through inhibiting the contact between poisons and metals,thus improving the stability of catalyst.Thispaper mainly studied about the core-shell catalysts encapsulated withmolecular sieve membrane possessing micropores and Metal Orgaic Frameworks（MOFs）,respectively. First,different synthesis methods were taken into consideration and parameters such as crystallization time,synthetic temperature and number of synthetic circle were investigated deliberately. Then the selective hydrogenation of olefins was employed to evaluate the catalytic performance of the resulted membrane encapsulated catalysts. At last, effects of molecular sieve membrane and MOFs membrane on the catalytic performance were discussed and the method of further optimizing the performance of the resulted catalysts are suggested.（1）silicalite-1 membrane encapsulatedPd/Al₂O₃scatalysts were designed and synthesized,with a thickness of 1 ?2 rnn, the membrane shows highselectivity for desired products and is resistant to sulfur-containing poison. Results of scanning electron microscope（SEM）showed that integrated and defect-free silica-1 membrane was formed onthe surfaceof Pd/Al203 catalystthrough secondary grouth method. Moreover, crystallite size and thickness of this microporous membrane could be adjusted by regulating crystallization time, synthetic temperature and number of synthetic circle. Compared with conventional catalysts, the Pd/AI2O3@silical-1 catalyst showed an excellentselectivity for desired product, but longer time was needed to achieve 100% convention of 1-hexene.In particularly,the catalyst with a crystallization time of 48 h exhibited the best performance for over it, 1-hexene conversion is as high as 100%, while conversion of cyclooctene is not detected, especially, with the existence of 2 wt% sulfur-containing poison, 96 % conversion of 1-hexene can still be obtained,38% higher than conversion over Pd/A^Oscatalyst under the same condition.（2）ZnO nano particles were first introduced to the surface of Pd/A^Os catalyst and then used as active sites for the formation of ZIF-8 membrane. The integrity of ZIF-8 shell was tested through the selective hydrogenation of olefins with different kinetic diameters.Results of SEM showed that ZnO introduced firstly could trigger the formation of ZIF-8 membrane and is usefial in enhancing the interaction between the layer of ZIF-8 membrane and the Fd/AhO^ core. Furttiermore, tiiis catalyst showed outstanding selectivity for olefinswith different kinetic diameters,excellent resistance tosxdfur-containing poison and leaching of Pd metal.（3） Benzothiazole was used as poison to test the anti-poison performance of different core-shell catalysts. The law concerning anti-poison ability and catalytic performance of core-shell catalysts were summarized and the type of materials forming the shell and its thickness were also discussed.