| The Pt clusters encapsulated in hybrid core-shell structures exhibit exceptional sizeselective catalysis in hydrogenation reaction for different molecular size olefin by the coupling of the molecular level pores and the catalytic activity of noble metal catalysts.The shell of the core-shell structure catalyst can effectively prevent the contact between the active component of the core and the toxic molecule,prevent the poisoning and deactivation of the catalyst.At the same time,the selectivity of the reaction can be improved due to the screening of the zeolite membrane pores.The multifunctional catalyst combines the advantages of crystal materials,metal materials,nano materials,etc.,and has wide application in the fields of molecular separation,catalytic reaction and sensorsZeolite with uniform topological structure,the molecular level of pore sizes and abundant acid sites and ZIFs with zeolite topology,adjustable aperture,functional diversity,high surface area and high stability and other advantages are widely used in the preparation of porous inorganic membrane.In this paper,the small pore LTA zeolite(diameter: 0.4 nm),SOD(0.3 nm)and zeolitic imidazolate frameworks ZIF-67(0.34 nm)were choosen as the inorganic porous film shell.The small pore opening allows small size molecules to enter but prevent large size molecules from contacting the platinum particles.It is crucial that the pore openings of the cages are sufficiently small to exclude hydrogen sulfide molecules(0.36 nm),the smallest sulfur-containing molecules in the hydro-treating process,while allowing hydrogen molecules(0.289 nm)and atomic hydrogen to diffuse in and out of the cage to produce hydrogen spillover.Our approach combines the concepts of size-selectivity and hydrogen spillover to the design of sulfur-tolerant catalysts.The contents include the preparation of three core-shell catalytic materials,the test selective hydrogenation reaction of olefin molecules,the test of the film integrity and structural stability,and the antipoisoning ability of the catalyst.The results show that the core-shell structure catalysts coated with molecular sieve membranes(LTA@Pt/Al2O3(PAA)and SOD@Pt/Al2O3(PAS))have been successfully synthesized by viscose-hydrothermal method with the thickness of the continuous and compact film were 2.1 μm and 5.3 μm,respectively.For the method of step-by-step,the crystal grow interactively so that the MOFs membrane was uniform and flawless,and the thickness is about 4.3 μm.The hydrogenation selectivity and structural stability of the core-shell catalysts were investigated using the mixture of hexene and cyclohexene as feeds.Using thiophene as the poison probe molecule,the antipoisoning properties of the catalysts were also examined.By comparing the experimental results,it was found that all the three core-shell structure catalysts had hydrogenation selectivity and sulfur resistance to a certain extent,and had higher catalytic activity after four times under the same reaction conditions.The core-shell catalyst coating with SOD membrane has the highest selectivity of hydrogenation and the most excellent antipoisoning ability,especially.Due to the aperture of SOD molecular sieve(0.3 nm)is the smallest among three materials,the uniform arrangement of the pore and the molecular level determines the size of molecular film inside the film.Only when the kinetic diameter of the molecule is smaller than that of the pore size of the membrane can the reactant enter the inner part of the film.In the reaction system,1-hexene which the kinetic diameter is 0.16 nm,can be freely diffused into and out of the membrane shell,and can be hydrogenated under the catalysis of noble metal,while cyclohexene(0.42 nm)and H2S(0.36 nm)were unable to enter the inner core of the pore to contact with the active component of the core to carry out the hydrogenation reaction because of its large molecular size,which the inorganic porous membrane has the most excellent performance of screening. |
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