Construction Of Core Shell Molecular Sieve Catalysts And Study On Their Catalytic Performance For Hydrogen Production By Steam Reforming Of Ethanol

As a clean,efficient and safe secondary energy resource,hydrogen energy is regarded as one of the future ways to solve energy resource problems and environmental crises.Ethanol steam reforming(ESR)have prospect application,and it has become a research emphasis in energy and catalysis fields.The key of catalytic technology is the development of efficient,low energy consumption,high thermal stability catalysts.Cobalt catalysts have good C-C fracture ability,and the price is low,exhibit high activity and selectivity of ethanol reforming.However,the anti-sintering and anti-carbon deposition properties of the catalysts remain to be further improved.In this paper,Beta and Y zeolite with high surface area and three-dimensional 12-ring pore system were chosen as carrier material,Silicalite-1(S-1)zeolite was a shell material.Combining the structural properties of core-shell composite molecular sieve with the catalytic activity characteristics of Cu,Co and Ni,we employed the impregnation and secondary growth method to prepare core shell double-carrier polymetallic catalysts and investigated the relationship between catalyst properties and the catalytic performance.The main research contents and conclusions are as follows:1.A group of xCuyNilOCo-S-1 catalysts supported on nano-S-1 zeolite were prepared by incipient-wetness impregnation method and its application in the reaction of ESR was investigated.Combining various characterization technologies for analysis and discussion with a focus on the structural characterization of the active sites,the effect of different amounts of Cu and Ni phases,catalytic activity and stability.The results show that when the main catalyst Co loading is 10 wt%,the addition of appropriate amounts Cu and Ni,the conversion of ethanol and the selectivity of H2 are obviously improved,and the stability of the catalyst is significantly improved.The 2.5Cu2.5NilOCo-S-1 catalyst exhibited very good catalytic performance and long-term stability.The conversion of ethanol and selectivity of hydrogen of catalyst was remained 100%and 72%,when the reaction time was 30 h,reaction temperature was 500 ℃,the molar ratio of water to ethanol was 6:1.This can be attributed to the doping of Ni enhances the cleavage of the C-C bond,the addition of Cu promotes the cleavage of the O-H bond,promotes the synergistic effect between Ni,Cu and Co,enhances the interaction between the metal and the support,inhibits the sintering of the active component,and reduces the product and carbon generation to improve catalyst stability.2.The xCuyNi-Beta@Co-S-1 core-shell catalysts were constructed with Cu-,Ni-modified Beta core and Co-based Silicalite-1 shell by combining seed induction secondary growth technique and incipient wetness impregnation method.The2.5Cu2.5Ni-Beta@Co-S-1 is a composite with a core of single Si-Beta crystal about 12 μm and a shell with a thickness about 50-80 nm.Compared with the catalytic performance of a single S-1 molecular sieve type catalyst,the 2.5Ni2.5Cu-Beta@Co-S-1 catalyst exhibited the highest selectivity of hydrogen,the lowest selectivity of by-products,the long-term stability and coking-resistance capability.When the molar ratio of water to alcohol was 3:1,500 ℃ for 21 h,there is no obvious inactivation,the conversion of ethanol was 100%,along with a certain amount of H2(72%),CO(4.1%),CH4(4.6%)and CO2(19%)as products.This is mainly attributed to the excellent textural properties.And the Ni,Cu nanoparticles which incorporated into the core-shell micro-composites protected the properties of active phases effectively.Moreover,the "purification effect" of the Co-base shell is conducive to obtaining high-purity hydrogen through a multiple reaction system.3.The core-shell zb2.5Cu2.5Ni-Y@Co-S-1,yw2.5Cu2.5Ni-Y@Co-S-1 and cz2.5Cu2.5Ni-Y@Co-S-1 catalysts were successfully constructed by stepwise synthesis method,in situ method and hard template method,which was further used to correlate their performance in ethanol steam reforming.The zb2.5Cu2.5Ni-Y@Co-S-1 catalyst revealed that the rattle-type structure displayed uniform morphology with diameters of 1.2 μm,the yw2.5Cu2.5Ni-Y@Co-S-1 catalyst particle size is about 2 μm and the cz2.5Cu2.5Ni-Y@Co-S-1 catalyst particle size is about 2.5 μm with high specific surface and good crystallinity.The size of the core is the same,and there is a significant difference in the thickness of the shell.This can be attributed to the fact that the crystallization solution of the Y molecular sieve during the synthesis of the yw2.5Ni2.5Cu-Y@Co-S-1 catalyst can provide partial "nutrients" for the growth of the shell.The presence of carbon during the synthesis of the cz2.5Cu2.5Ni-Y@Co-S-1 catalyst favors the growth of the shell,while the removal of carbon increases the porosity.At the reaction temperature of 450 ℃,the results of catalytic testing,comparisons with the others catalysts,showed that cz2.5Cu2.5Ni-Y@Co-S-1 had high catalytic activity(100%),hydrogen selectivity(69%)and stability for 28 h.This is due to the multiple reaction of the catalyst on the reactant molecules from the core phase to the shell to the core phase,increasing the effective catalytic activity center,and enriching the pore structure in the reaction.The spatial structure plays a buffering role,increases the concentration of reactants in the microenvironment,enhances the interaction between the reactant molecules and the active components,further realizes the catalytic effect of purifying and purifying,and improves the yield of H2 under low temperature conditions.