The Preparation Of Anti-toxic Core-shell Catalytic Materials And Study On Hydrogen Spillover Mechanism

The core-shell catalysts as a kind of multi-functional catalytic materials integrate the inner and outer materials which have complementary advantages.The shell materials can improve the selectivity of the reaction,effectively prevent the contact between toxic molecules and active components,prevent the leaching of active components,thereby improving the catalytic activity and stability of the catalyst.The property of shell materials is vital for core-shell catalysts.Metal organic frameworks materials,which are self-assembled by the coordination of metal clusters and organic ligands,have zeolite topology,adjustable pore size and controllable functional groups;Zeolite molecular sieve nanomaterials have molecular-level channels and homogeneous cavity;New carbon materials have high specific surface area and high stability;Therefore,metal organic frameworks,zeolite molecular sieve,and new carbon materials are ideal for shell materials.The Pt/Al₂O₃@ZIF-67 core-shell catalyst with ZIF-67 zeolite imidazole framework shell membrane was synthesized by layered self-assembly method,and the shell thickness of ZIF-67 can be controlled by impregnation times.Compared with Pt/Al₂O₃ catalyst,Pt/Al₂O₃@ZIF-67 catalyst exhibits excellent hydrogenation selectivity for 1-hexene in alkenes hydrogenation reaction（hexene 0.17 nm,cyclohexene 0.42 nm,cyclooctene 0.55 nm）,due to the special channel size（0.36 nm）of ZIF-67.At the same time,Pt/Al₂O₃@ZIF-67showed good sulfur resistance and stability.The Pt/Al₂O₃@SOD core-shell catalyst（PAS）with SOD shell membrane was synthesized by microwave synthesis,and the shell thickness of SOD shell was 5.3 um.The cages of the SOD are sufficiently small（0.3 nm）to exclude the smallest sulfur-containing molecules（hydrogen sulfide,0.36 nm）,while the kinetic diameter of hydrogen（0.289 nm）is less than the pore size of the sodalite cage,and hydrogen molecules can pass freely through the SOD shell and dissociate into active hydrogen atoms on the active Pt centers.The active hydrogen atoms diffuse out from the shell,then to the active sites of the Co Mo catalyst,where the hydrodesulfurization reaction is performed.As a result,the catalytic activity of the Co Mo was significantly improved due to the hydrogen spillover.At the same time,the hydrogenolysis pathway（DDS）of DBT is promoted due to the hydrogen spillover effect.With the increase of reaction temperature,the S_DDS/HYDvalue increases and the selectivity of DDS increases.At the same conversion rate,the catalytic temperature of PSCM catalyst is 50^oC lower than that of Co Mo catalyst,which has great potential for industrial application.The exxcellent catalytic performance of PSCM catalyst lays a foundation for the application of hydrogen spillover in catalytic field.In order to study the effect of shell conductivity on hydrogen spillover,Pt/Al₂O₃@GO catalyst（PAG）with GO as shell material was synthesized by microwave method.It was found that the catalytic activity of PGCM catalyst was lower than that of PSCM catalyst.At the same time,GO shell can not completely block the poisoning of Pt by H₂S,and the sulfur resistance of PGCM catalyst is weaker than that of PSCM catalyst.The results show that the hydrogen spillover effect of PGCM catalyst is weaker than that of PSCM catalyst,and the conductivity of the shell has no significant effect on the long-distance transfer of active hydrogen from one catalyst to another.