Construction Of Core-shell Type Microreactor And Their Catalytic Performance For Ethanol Steam Reforming

Hydrogen as an ideal clean energy has been widely used in the fields of petrochemical industry,metallurgy,food processing and aerospace.Renewable resources are an efficient and environmentally friendly route for producing hydrogen and has been studied extensively in recent years.In addition to sustainability issues,bioethanol has increased interest for various applications because of the high energy,high H2 yield,low toxicity and safe to handle.Ethanol steam reforming?ESR?is considered a promising technology for producing hydrogen by atom-economy.However,it is well-known that the ESR as an equilibrium reaction has a complex reaction network and derives numerous products,which is strongly affected by the type of catalysts and environmental conditions.Therefore,in order to improve the catalytic performance and reduce energy consumption,the current research focuses on the development of high activity,selectivity and stability catalyst for the efficient ESR reaction.In this thesis,Beta zeolite with high surface area and three-dimensional12-ring pore system was chosen as carrier material.Combined with space advantage of core-shell structure and mechanism of multistage reactor,we employed a variety of synthetic methods to build a series of core-shell structure microreactor and investigated the relationship between catalyst properties and the catalytic performance.The research contents and conclusions are shown as following:1.A group of multi-functional xFey Cu10Ni-Beta catalysts supported on nano-Beta zeolite was prepared by an incipient wetness impregnation method.The xFeyCu10Ni-Beta catalysts were studied using the kinds of characterization technologies with a focus on the structural characterization of the active sites,the effect of different amounts of Cu and Fe phases and understanding the reaction pathway for the catalysts.The 1.5Fe1.5Cu10Ni-Beta catalyst exhibited very good catalytic performance and long-term stability.The activity and selectivity towards different products remained quite constant throughout the 28 h test,such as 100 % conversion of ethanol and 70 % H2 selectivity.The analyses of catalyst by XAFS techniques suggest that the Fe phase,which has a tendency to be enriched on the alloy particle surface,is suitable for acetaldehyde and CH4 reforming.2.The xCu/yFe-Beta@Ni-Beta core-shell catalysts consisting of an all-silica Beta core supporting Cu and Fe and a Ni-based nano-Beta shell were prepared by secondary growth and incipient wetness impregnation method.The2.5Cu2.5Fe-Beta@Ni-Beta is a composite with a core of single Si-Beta crystaland a shell with a thickness about 300-500 nm.And it shows that the high dispersion and uniform diameter of the Ni nano-particles?13.6 nm?are supported on the external surface of the shell Al-Beta.The2.5Cu/2.5Fe-Beta@Ni-Beta catalyst exhibited catalytic performance and long-term stability at 500 °C.The activity and selectivity towards different products remain almost constant in the 8 h test,such as 100 % ethanol conversion and 71 % H2 selectivity.The XANES analysis of the catalysts is shown that the spectra of Ni and Cu matched quite well with metallic Ni and Cu standard.The Fe K-edge spectra showed that the catalysts had characteristic pre-edge absorption of Fe metal and oxide.Compared to Beta zeolite as support,the 2.5Cu/2.5Fe-Beta@Ni-Beta catalyst exhibited excellent catalytic performance.The effect of the nature of the double-support and promotion on adding Ni,Cu and Fe was indicated that the special structural advantages of the core-shell support could give full play to the properties of active phases.3.A hollow spherical Pt@HBS catalyst was successfully fabricated through an organotemplate-free and hard template route.We report a simple method for the preparation of well-dispersed Pt nanoparticles in hollow Pt@HBS to obtain the excellent catalytic performance of the LT-ESR.The physico-chemical properties of the catalysts and catalytic activity of different Pt loadings were analyzed by various characterization methods.The results showed that the Pt@HBS catalyst with complete hollow structure exhibited very uniform in size?1.3 ?m?and uniform thickness of shell about 220 nm.The 2Pt@HBS presentedhigh conversion?98 %?and H2 selectivity?70 %?around the 28 h test.Compared with 2Pt-Beta catalyst,such high-purity hydrogen and low byproducts selectivity of Pt@HBS can be explained by the synergistic effect of the special hollow structure and metal Pt endows the catalysts with high efficiency.Moreover,the existence of the hollow structure is significant for successfully promoting the excellent catalytic performance and high stability during the LT-ESR reaction.4.Constructing the structure of nano-materials is important in the catalytic reaction,since it can address the problem of the increase in undesired products.Combined with the advantages of sacrificial template and hard template method,we developed a resorcinol-formaldehyde?RF?polymer resin layer for assisted synthesis of hollow Pt@NHB catalyst.The Pt@NHB catalyst possessed discrete and spherical hollow structure?500 nm in diameter?with the homogeneous shell thickness of 40 nm.The Pt phase in the beta shell possesses a relatively narrow size range with the most probable size of about 2.5 nm.It had employed a series of LT-ESR catalytic tests to elucidate the catalytic performance of the Pt@NHB,with a focus on the structure-activity relationship and reaction mechanism.The results of steady-state-activity testing,comparisons with those from Pt-beta and Pt-SiO₂ catalysts showed that the Pt@NHB exhibited superior activity,stability and low by-products.At the reaction temperature of 350 oC,the ethanol conversion has been attained about 100 %,along with a certain amount of H2?68.7 %?,CO₂?21.2 %?,CO?3 %?and CH4?7 %?as products.The C-Pt@NHBcatalyst was not good enough for the catalysis of LT-ESR after 12 h,the conversion of ethanol decreased significantly from 98 % to 76 % and the H2 selectivity reduced to 51.7 % at the end of the test.The hindering effect of zeolite shell could effectively improve the concentration of relatively large molecules?i.e.,ethanol and acetaldehyde?in the hollow micro-environment and promote the molecules reacted with Pt active sites to achieve a complete catalytic conversion.Moreover,due to the “purification effect” for the undesired products,the existence of a large number of catalysts in the reaction system can obtain high-purity hydrogen production.5.Combined with the catalytic advantages of core-shell catalyst and hollow catalyst,we designed a rattle-type catalytic material.We describe a novel route for the preparation of CeO₂@Pt-Beta catalyst by seed-directed route with the assistance of RF,a hard template for hollow interlayer.SEM and TEM images of CeO₂@Pt-Beta catalyst revealed that the rattle-type structure displayed uniform morphology with diameters of 1.2-1.5 ?m and the shell with a thickness about80-100 nm.Due to CeO₂ catalytic performance and unique structural advantages?hollow structure and core-shell type?,the CeO₂@Pt-Beta catalyst exhibited excellent catalytic performance in ESR as structured catalysts.The results of catalytic testing,comparisons with those from Pt-Beta catalyst showed that CeO₂@Pt-Beta had high catalytic activity?100 %?,hydrogen selectivity?65 %?and stability.This design opens up new possibilities for constructing rattle-type catalytic material,which will be of great promise for the development of ESRcatalyst.