The Preparation Of Novel La₂Mo₂O₉-based Solid Electrolytes And Its Application In Electrochemical Synthesis Of Ammonia

Synthesis ammonia electrically at atmospheric pressure has received much attention since firstly reported in《SCIENCE》.at 1995 by George Marnllos, which surmount the limit of thermodynamics in traditional Haber method of ammonia synthesis and boost a great leap in the method study of ammonia synthesis.The sticking point of electrically ammonia synthesis is electrolytic conductors, which have excellent electric conductivity and function in low temperature. Based on reviewing their development, these dissertations focuses on lanthanum molybdate -based novel ion conductors, and study their proton conductivity in reduction atmosphere. The parent compound lanthanum molybdate undergoes a phase transition at 580℃and the structural instabilities may limit the prospects of using it in services. Therefore, suppressing this structural transition may be a good way. In this studies, we attempted to dope other metallic elements at La site based on lanthanum molybdate to form solid solution by citrate methods, and the thermal decomposition was characterized by thermal analysis(TG—DTA),from which the optimum calcinations temperature was obtained. The topography was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM).The crystal structure was confirmed by power X-ray diffraction (XRD). Using the sintered complex oxides as solid electrolyte, ionic conduction was systematically studied under different atmosphere. Results show that suitable concentration doping with calcium; strontium; potassium can restrain phase transition, which would enhance the ionic conduction during low temperature and bring down the ionic conduction during high temperature. The doping with rare earth elements can't restrain phase transition, but can depress the temperature of phase transition. Oxide-salt composite electrolytes are a new type of intermediate and low temperature solid state conductors. In order to enhance the ionic conductivity of lanthanum molybdate, two new types of oxide-salt composite electrolytes: lanthanum molybdate-potassium orthophosphate -calcium orthophosphate and lanthanum molybdate-sodium chloride-strontium chloride were prepared by mixing the lanthanum molybdate,phosphates and chlorides. The influence of crystal structure and topography from salt were confirmed by power X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results of ionic conductivity test declare that salt can't restrain phase transition of lanthanum molybdate,but can heighten the ionic conductivity.Ammonia synthesis from nitrogen and hydrogen, at atmospheric pressure using solid-state proton conductors as the electrolytes, has been investigated extensively. Relatively, directly use natural gas to synthesize ammonia is a low-cost and competitive route. In this paper, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in the solid states proton conducting cell reactor by electrochemical methods. At the same time,attempt to synthesize ammonia use natural gas and nitrogen. The optimum temperature and potential factor are studied as the function of rates of ammonia formation. And all of the samples produce ammonia to different degrees. The possible mechanism of ammonia synthesis with the use of solid state proton conductors from natural gas and nitrogen was explored; the component of natural gas and tail gas used in this experiment was determined by gas chromatography analysis, the results show that tail gas contain not only ammonia but also ethane, which boost a great leap in realizing the application of electrically ammonia synthesis in industrial production.There are lots of works to do in synthesizing ammonia at atmospheric pressure with the use of solid state electrolyte in the future. In this paper, problems, possible solutions and future opportunities for further development are given.