| In recent years,the excessive combustion of fossil fuels has emitted a large amount of CO2,making the greenhouse effect and global warming increasingly prominent,while the natural resource reserves are limited,the development and utilization of renewable energy has become a global research hotspot.As a clean,efficient and low-carbon secondary energy source,hydrogen energy is widely used in the fields of energy,transportation,and industry.Hydrogen fuel cells are considered to be the most promising way to utilize hydrogen energy,among which proton exchange membrane fuel cells,as the core of fuel cell vehicles,have extremely high requirements for hydrogen purity.The water gas shift(WGS)reaction is an effective method to eliminate residual CO in reforming gas and purify H2,and the high purity hydrogen produced is widely used in hydrogen fuel cells.In addition,the ammonia decomposition to hydrogen reaction can produce high purity hydrogen without COx for the proton exchange membrane fuel cell,which is also of great research importance.Therefore,the exploration of catalysts with high activity and stability for water gas shift and ammonia decomposition reactions is especially critical for the large-scale application of proton exchange membrane fuel cells.This thesis focuses on rare earth oxide-based catalytic materials and investigates the application of these materials as promoters and supports in hydrogen production reactions.Firstly,for ammonia decomposition reaction,the catalytic activity of ammonia decomposition was greatly enhanced by modulating Ru/Al2O3 catalyst with small amount of CeO2 as promoters;for WGS reaction,Sm2O3 was selected as a support and loaded with active metal Ni to obtain excellent performance of water gas shift reaction.In addition,combined with a series of in-situ and ex-situ characterizations,the interaction between rare earth oxides as promoters or supports and the active metals was revealed,and the reasons for the increased activity of catalysts were explained.This provides a new idea for the expansion and application of rare earth oxid-based catalytic materials.The specific research contents of this work are as follows.1.CeO2-x modified Ru/γ-Al2O3 catalysts for ammonia decomposition reactionDeveloping high-performance ammonia decomposition catalysts for preparing COx-free hydrogen shows great practical significance.Herein,CeO2 is used as a promoter to modulate the metal-support interaction to enhance the catalytic performance of Ru/AlO3 catalysts.In this work,we loaded a small amount of CeO2 nanoparticles on the surface of γ-Al2O3 by a facile colloidal deposition method,and further loaded a certain amount of Ru by colloidal deposition method to obtain a series of 1Ru/xCe-10Al(x=0.5,1,or 3)catalysts.We found that the optimized 1Ru/1Ce-10A1 catalyst exhibited excellent activity for the decomposition of ammonia with a very high hydrogen yield of 7,097 mmolH2 gRu-1·min-1 at 450℃.The morphology was characterized by HRTEM,and Ru species were highly dispersed in small clusters of about 1.3 nm before and after the reaction.Furthermore,combined with the H2-TPR and XPS characterization results,due to the interaction between Ru species and partially reduced CeO2-x,the electron density of Ru species was increased,which was conducive to the desorption of N2,and this was the internal reason for the enhanced activity of 1Ru/xCe-10Al catalysts.This work chooses CeO2 as a promoter for support modification,which provides a simple and effective strategy for the design of high-performance ammonia decomposition catalysts.2.Efficient Ni/Sm2O3 catalysts for water gas shift reactionAs an effective method to eliminate CO in reforming gas,water gas shift reaction plays an important role in hydrogen purification of proton exchange membrane fuel cells.In this work,a novel Ni/Sm2O3 catalyst for water gas shift reaction was successfully prepared using rare earth oxide Sm2O3 as support.Firstly,we synthesized Sm2O3 nanoroads by hydrothermal method and and successfully prepared xNi/Sm2O3 catalysts with different Ni loadings by deposition precipitation method.The Ni/Sm2O3 catalysts were used in the WGS reaction for activity evaluation,where the 20Ni/Sm2O3 catalyst showed very high activity and stability,and the reaction rate was 20.6 mmolco·gcat-1·s-1 at 250℃.The results of HRTEM characterization showed that Ni species always existed in the form of small particles after reduction and reaction.Combined with H2-TPR,XPS and a series of infrared characterization,it was confirmed that Niδ+and Ni0 species coexisted,while the Ni0 species was the main active site of WGS reaction catalyzed by Ni/Sm2O3 catalyst.In addition,TPSR as well as kinetic isotope experiments indicated the dissociation of H2O was the decisive step of Ni/Sm2O3 catalyst in WGS reaction.This work provides a new way for the design and preparation of highly efficient rare earth-based WGS reaction catalysts. |
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