Study On The Characteristics Of CH₄ Synergistic Cerium-based Thermochemical Circulating Water For Hydrogen Production

Solar thermochemical cycle splitting H₂O based on ceria-based oxide allows for effective storing of solar radiation while producing renewable fuel.The extreme high reduction temperature(1400°C)and low partial oxygen pressure(below 1×10^-5 bar)of the reduction step,however,are disadvantages of this cycle.The addition of CH₄ to ceria-based oxide appears to be a promising way for enhancing reactivity.In order to enhance the efficiency of CH₄ synergizing with ceria-based oxide thermochemical H₂O splitting for hydrogen,this study uses CeO₂ as the carrier and adds Ni portion on the basis of Zr⁴⁺doping.From the establishment of the system of CH₄ synergizing with ceria-based oxide thermochemical H₂O splitting for hydrogen to the physical and chemical properties of ceria-based under Zr⁴⁺doping and Ni loading,and the reaction characteristics of the thermochemical H₂O splitting,this paper employs the method of theoretical analysis and experimental study.The results obtained are summarized as follow:(1)Thermodynamics of CH₄ synergizing with CeO₂ thermochemical H₂O splitting for hydrogen was analyzed using the principle of minimizing Gibbs free energy,and the feasibility and benefits of CH₄ synergizing with CeO₂ reduction were confirmed;thermodynamic model of CH₄ synergizing with CeO₂ thermochemical H₂O splitting system was built and carried out under various reaction conditions to simulate the distribution of product components.The results show that the reaction conditions are900-1000°C isothermal cycle at normal pressure,with a molar ratio of CH₄/CeO₂ of0.45 and a molar ratio of H₂O/CeO₂ of 0.5.(2)Cerium-zirconium oxide Ce_1-xZr_xO₂(x=0-0.4)were synthesized by co-precipitating Zr⁴⁺into CeO₂.Ce_1-xZr_xO₂ were characterized in terms of its physical and chemical properties.And the reaction characteristics and stability of the Ce_1-xZr_xO₂were investigated in a fixed bed reactor at 900°C.The results show that Zr⁴⁺doping induces lattice distortion of CeO₂,prevents CeO₂ sintering,facilitates the production of oxygen defects,and increases the function and migration potential of adsorbed molecular oxygen on the surface and internal lattice oxygen.The reactivity of Ce_1-xZr_xO₂ is much higher than that of CeO₂.As the mole content of Zr doped increases,the reactivity increases at first,then decreases.The best concentration Zr⁴⁺dopant is 20molar percent,with 1.18 mmol/g of H₂ production and H₂/CO molar ratio similar to 2.During 60-cycle reaction,Ce_0.8Zr_0.2O₂ redox ability remains stable.(3)The immersion approach was used to load Ni on Ce_0.8Zr_0.2O₂(C8Z2)to prepare supported m Ni/C8Z2(m=0-0.09 percent).According to physical and chemical characterization and fixed-bed reactivity tests,Ni extends the pore structure,increases active sites,and improves surface adsorption molecular oxygen and internal lattice oxygen migration ability;m Ni/C8Z2 reactivity increases first and then decreases with increasing Ni loading;0.05Ni/C8Z2 owns the best reactivity,and the amount of H₂produced is 1.57 mmol/g.0.05Ni/C8Z2 redox ability remains stable after 60 cycles.