Construction Of High Efficiency Catalyst Based On Silica And Their Catalytic Performance For Ethanol Steam Reforming

To date,steam reforming of ethanol(ESR)stands out among various hydrogen production strategies not only for the high H₂yield but also for the less toxic character of the reactant,which can be abundantly derived from biomass sources.Therefore,high-efficiency ESR catalyst with cheap,high-efficiency,good stability has become the focus of research in this field.SiO₂has been reported as a commonest and widely used support materials for ESR reaction due to its high hydrothermal stability,porosity,controllable structure and diverse synthesis methods.However,there are some drawbacks in traditional porous silica materials can not statisfy the requirements of the stable and efficient hydrogen production in ESR reaction,such as low efficiency of active metals and insufficient stability of the catalyst.And realize the efficient utilization of active metals by adjusting the structure of catalyst has become the development direction of ESR catalyst.It is greatly significant to study and prepare efficient catalysts with high catalytic efficiency,good sintering resistance and carbon deposition resistance.In this thesis,porous SiO₂was chosen as carrier material constructing a series of high efficient catalysts according to the drawbacks of traditional porous SiO₂.Combined with the advantages of bimetallic synergistic catalysis,we employed a variety of synthetic methods to build efficient catalyst with high catalytic efficiency,sintering resistance as well as carbon deposition resistance during ESR reaction and investigated the relationship between catalyst properties and the catalytic performance.The research contents and conclusions are shown as following:1.Mesoporous silica with yolk-shell structure(HS)was one-step synthesized by modified St(?)ber method with using PVP and CTAB as dual-templates and TEOS as silicon source.Pt-Pd/HS catalyst was prepared by co-impregnation method using a mixed aqueous solution of Pt and Cu precursor.TEM analysis showed that the Pt-Pd/HS catalyst posses an clear ellipsoidal yolk-shell structure with long axis and short axis size of 200 nm and 100 nm,respectively,while the shell of?10 nm.Compared with the Pt-Pd/SS catalyst,the Pt-Pd/HS catalyst exhibited higher ethanol conversion(99.69%)and hydrogen selectivity(66.95%),and remained stable during the 30 h stability test.The yolk-shell structure with multiple loading surfaces can not only effectively improve the dispersion of active components but also promote the enrichment of reactant molecules to some extent,which could give full play to the synergy between bimetallic active and thus improve the catalytic efficiency.In addition,the thin shell of HS is beneficial for the diffusion and mass transfer of reactants and products and thus improve the catalytic activity.2.Uniform Pt-Cu alloy particles(?50 nm)were synthesized via glycine mediated method,and then multiple Pt-Cu alloy particles were embedded in the mesoporous SiO₂by modified St(?)ber method to prepare a core-shell structure Pt-Cu@MS catalyst for ESR reaction.Structural and morphological analysis shows that the Pt-Cu@MS catalyst(?400 nm)has a uniform dragon fruit-like structure.The channels of the shell could provide efficient channels for mass transfer and ESR reaction.Compared with Pt@MS,Cu@MS and supported Pt-Cu/MS catalysts,it was found that the dragon fruit-like Pt-Cu@MS nanocomposite with optimal Pt/Cu ratio as a promising catalyst exhibited excellent catalytic activity and long-term stability with high H₂selectivity and low by-products for the ESR.The shell of the Pt-Cu@MS catalyst not only make the embedded Pt-Cu alloy nanoparticles easily accessible but also effectively prevent leaching and aggregation of active sites,thus maintain a good catalytic activity during the stability test.3.A facile reverse micelle strategy has adopted to prepare a core@shell structure Ni-Cu@Ca-S nanocatalyst(?14.3 nm)composed of an ultra-small Ni-Cu alloy(?2.8 nm)encapsulated in Ca-functionalized SiO₂nanoparticles.Benefiting from its core@shell structural features and unique components,the Ni-Cu@Ca-S nanocatalyst exhibited superior activity(69.91%H₂selectivity and 99.99%ethanol conversion)and stability compared to reference samples.The regenerated Ni-Cu@Ca-S nanocatalyst showed high stability,maintaining 98.14%ethanol conversion and only 1.98 mg g_cat^-1h^-1in carbon deposition.The high catalytic performance of Ni-Cu@Ca-S is attributed to not only its encapsulated structure,which effectively prevented the sintering of neighboring Ni-Cu alloy nanoparticles,but also to its Ca-functionalized porous SiO₂shell,suppressing the carbon deposition.Moreover,the porous thin shell of Ni-Cu@Ca-S facilitated the mass transfer and diffusion of reactants and products.4.Combined with the unique core-shell structure advantages and the characteristics of the small size of the metal nanoparticles,we reported a strategy to encapsulate Pt-Cu alloy nanoparticles(?3 nm)in a porous SiO₂shell with multiple Ni nanoparticle anchored on the shell as a core-shell structured Pt-Cu@Ni-S nanocatalyst(?14.9 nm)in a reverse micelles system.The porous thin shell of Pt-Cu@Ni-S could facilitate mass transfer and improve the catalytic activity.Compared with other catalysts,the Pt-Cu@Ni-S nanocatalyst exhibited higher ethanol conversion(99.99%),H₂selectivity(70.32%)and an excellent stability with no loss of activity after 50 h of reaction at 450?.The unique core-shell structure could provide a great opportunity to give full play to the catalytic activity of active sites,improve the H₂selectivity and elimination by-products during the ESR reaction.