Mechanistic Investigations On Metal-Support Interaction Of Ni-based Catalysts For Ethanol Steam Reforming

Hydrogen is a clean and efficienct fuel with great potential for various applications.However,most hydrogen in the industry is produced from fossil fuels.The dependence of fossil fuels makes these processes nonrenewable with enormous CO2 emissions.Ethanol can be produced on a large scale by fermentation of a variety of biomass.With the high hydrogen-to-carbon ratio,ethanol is a promising renewable feedstock for hydrogen production.However,Ni-based catalysts for ethanol steam reforming suffer from deactivation due to carbon deposition and sintering of Ni at high temperature.Strong endotherm of steam reforming also exacerbates the energy consumption of hydrogen production via ethanol reforming technology.In this dissertation,a series of efficient and stable nickel-based catalysts are designed and synthesized based on metal-support interaction to inhibit carbon deposition and metal sintering in the ethanol reforming for hydrogen production.Ni nanoparticles are dispersed and stabilized by enhanced metal-support interaction and dynamic equilibrium between ethanol oxidative decomposition and water activation is achieved by the regulation of metal-support interaction.Construction of an ordered mesoporous structure inhibits the migration process of Ni species under high temperature reaction conditions.Ordered mesoporous structure Al2O3 is synthesized by the evaporation-guided self-assembly method.The mesoporous structure enhances interaction between Ni and Al2O3,suppressing the sintering of Ni.Mg O was introduced to adjust the acidity of the support and inhibit the formation of carbon deposition.The ethanol conversion rate keeps stable in 30 h stability test.The influence of Sn addition on catalytic properties of Ni-Ce O2 is studied.With the modification of undercoordinated Ni sites by Sn atoms,Ni Sn surface alloy suppresses the formation of carbon on the surface area of metallic Ni and improves the stability of Ni/Ce O2 catalyst.Moreover,the introduction of Sn tunes the interaction between Ni and Ce O2,which regulates oxygen mobility and the reaction pathway of ethanol steam reforming on the surface of Ni/Ce O2,The ratio of Ni⁰/Ni²⁺sites in the Ni/Ni_xMg1-x O system is adjustable through a stepwise non-equilibrium method.The lattice matching of Ni and Ni_xMg1-x O achieves a high degree of dispersion and stable localization of metallic Ni.Under the synergistic effect of catalysis of C–C bond cleavage on adjacent Ni⁰ sites and activation of*CHx dehydrogenation on Ni²⁺sites,high H2 selectivity and stability can be achieved on the surface of Ni/Ni_xMg1-x O with suitable Ni⁰/Ni²⁺site using ethanol as raw material for hydrogen production.Ni_xMg1-x O solid solution is used as a novel oxygen carrier in the process of ethanol chemical looping steam reforming for hydrogen production by changing Mg²⁺concentration in solid solution to regulate oxygen activity.With the cooperation of bulk oxygen and the catalysis of metal Ni,the solid-solution-type oxygen carrier achieves78.7%hydrogen selectivity with a steam-to-carbon ratio of 1.The solid-solution-type oxygen carrier maintained stable during 30 cycles of autothermal operation.The structure of Ni_xMg1-x O solid solution can be recovered through oxidation regeneration at 600°C.This study provides new ideas for hydrogen production via efficient,stable and energy-saving ethanol reforming technology.