Investigation On Catalytic Combustion Of Cu-based Thin Films Material For Energy And Environmental Applications

In the 21^st century,energy and environment are the two vital issues for the whole world.Fossil fuels will remain the most important energy resource in the future decades,but the combustion of fossil fuel brings about serious environmental problems.Volatile organic compounds（VOCs）and carbon monoxide（CO）,which mainly originated from the combustion of fossil fuels are serious air pollutants that may give rise to deleterious human health and environmental effects.Catalytic combustion of VOCs and CO is one of the most promising technologies for pollutants abatement,which is highly desirable to proceed regarding the low cost,energy savings,safety and environmental friendliness.In this dissertation,aiming at resolving the key problems of catalytic combustion of VOCs and CO,fundamental studies and various design aspects of Cu-based heterogeneous catalysis have been taken into consideration.Furthermore,preparation of novel Cu-based binary and ternary oxides thin film catalysts by pulsed-spray evaporation chemical vapor deposition（PSE-CVD）method,characterization of thin films in terms of morphology,structure and composition,the relationships between physicochemical properties and catalytic performances,catalysts durability,effects of reaction parameters with high gas hour space velocity（GHSV）,catalytic mechanisms,effects of support and CO₂ under realistic condition,reaction kinetics as well as density functional theory（DFT）modeling are discussed in detail.Thus,both process and theoretical bases are supplied for the catalytic combustion aspects of Cu-based thin films in this dissertation.The main achievements and progress of this dissertation are as follows:1)A series of Co-Cu binary oxides thin films dispersed homogenously on an inert support were newly prepared by PSE-CVD for kinetic study of catalytic combustion.The physicochemical properties of the as-prepared thin film were comprehensively characterized.The results disclosed the formation of cubic binary oxides with the amorphous surface.With the progressive introduction of Cu into the Co spinel,the crystallite size tended to increase due to the incorporation of large Cu²⁺ionic radius.Co³⁺,Co²⁺,Cu²⁺,lattice and adsorbed oxygen species were confirmed to co-exist at the surface of the binary oxides thin film.The obtained samples exhibited excellent performance for propene（C₃H₆）oxidation with a high GHSV of 150,000 mL·g^-1·h^-1.The light-off curves shifted towards lower temperature with more Cu incorporation,which was linked to the increase of Co³⁺/Co²⁺,the rearrangement and synergetic effects of Co,Cu and lattice oxygen.The reaction rate increases with the increase of C₃H₆ concentration by following r=1.12*[C₃H₆]^0.27,without reaching the kinetic limitation stage.Moreover,an attractive durability of the binary oxides thin film was observed in the C₃H₆ oxidation during 50 hours.2)Synthesis and catalytic properties of Fe-Cu binary oxides thin films through doping strategy with different Fe/Cu molar ratios via one-step PSE-CVD method were evaluated.Structure analysis of the as-prepared thin film reveals the formation of single-phase delafossite structure.A smooth hollows film surface with an agglomerated crystallite grains was observed.With the introduction of Cu content,Cu⁺was successfully embedded in Fe₂O₃ lattice to form substituted spinel.Also,the ratio of O_Latt/O_Ads and electrical resistivity showed increasing trends.The perceived behavior was ascribed to the progressive incorporation of Cu,which bought structural changes favoring the formation of anionic vacancies and the restraint of oxygen mobility.The catalytic activity was investigated through the complete oxidation of CO with a high GHSV of 184,500 mL·g^-1·h^-1,which is closed to semi-industrial scale.The introduction of a higher amount of Cu shifted the light-off curves toward lower temperatures,due to the high dispersion of Cu and highly active surface oxygen contents observed by characterization.In addition,the influence of the presence of CO₂ in the reaction mixture was studied to evaluate the capability of the as-prepared thin film under realistic reaction conditions.Although the principal inhibitor effect associated with the CO₂,the progressive introduction of CO₂ in the reaction,gave rise to a decrease of the CO conversion.Furthermore,theoretical calculations based on DFT method of CO with CO₂ oxidation over CuFeO₂ delafossite film surface catalyst demonstrated that the existence of CO₂ act as an inhibitor in the CO adsorption process which lead the reaction to a higher temperature.Moreover,the study of kinetics and mechanism of CO oxidation over catalyst surface was performed,then a detailed mechanism and a kinetic model which can simulate the experimental surface reaction results were achieved with a reasonable agreement.3)A novel thin film of Cu-Co-Fe ternary oxides dispersed homogenously on an inert support was prepared by PSE-CVD for catalytic combustion of CO.The physicochemical properties of as-prepared ternary oxides thin film were comprehensively characterized by various techniques.The results disclosed the formation of amorphous structure of ternary oxides with dome-top-shaped morphology which supplied abundant sites for oxygen evolution.Moreover,Co³⁺,Fe³⁺,Cu²⁺,lattice and adsorbed oxygen species were confirmed to co-exist at the surface and provided effectual synergetic effects for the oxidation reaction.The optical bandgap energies （1.5 and 2.05 eV）of as-prepared ternary oxides thin film were lower than their base metal oxide counterparts（2.15-2.18 eV）,which enhanced their reducibility due to easier lattice oxygen mobility.The Cu-Co-Fe ternary oxides thin film revealed attractive performance for CO oxidation and complete conversion was achieved at a much lower temperature about 100-200°C as compared to the reported metal oxides.The superior performance was linked to the formation of lattice and adsorbed oxygen species,synergetic effects of Cu²⁺,Co³⁺and Fe³⁺,high reducibility and excessive oxygen mobility.The ternary oxides thin film exhibited attractive stability and the conversion of CO remained almost constant throughout the 30 hours.4)The effect of inert and active substrates on the catalytic activity and stability of non-crystal Fe-Co-Cu ternary oxides thin film deposited on stainless steel grid mesh （SSGM）and copper grid mesh（CUGM）by PSE-CVD method was investigated for CO oxidation.The Fe-Co-Cu ternary oxides thin film was thoroughly characterized.The obtained results showed that the performance and stability depended on the nature of the interphase between the metal substrate and the deposited ternary oxides thin film.The physicochemical properties disclosed the formation of needle-like shaped morphology,which leading to sufficient contact area for oxygenated species with amorphous structure of ternary oxides and provided abundant sites for oxygen evolution.Moreover,metallic species(Fe³⁺,Co³⁺,Co²⁺and Cu²⁺)and electrophilic oxygenated species(O₂^2-or O^-)were confirmed to co-exist at the surface and offered effectual synergetic effects on oxidation reaction with better reducibility.The open porosity of nano-grains,abundance of surface metallic and mobility of lattice oxygen,thermal and electrical conductivities,high reducibility at low temperature due to low optical bandgap energies played together a crucial role in the catalytic oxidation reaction.The as-prepared ternary oxides thin film exhibited attractive performance towards the total oxidation of CO with a high GHSV of 81,818 mL·g^-1·h^-1.The light-off curves shifted towards lower temperature,when ternary oxides thin film deposited on CUGM and used in the reaction.Therefore,the doping strategy of active substrate （in the absence of any other oxygen promoter and noble metals support）was used to adapt highly active Fe-Co-Cu ternary oxides at low temperature,which could further be an auspicious way to significantly increase the activity of ternary oxides for catalytic combustion applications.In conclusion,this dissertation provides effective and meaningful investigation on the synthesis of Cu-based binary and ternary transition metal oxides（TMOs）thin films by PSE-CVD and their performance towards complete catalytic combustion of VOCs and CO.Because it not only facilities to reduce VOCs and CO emission to the atmosphere,but also reveals economic benefits.Based on the performed experiments,we explore the characterization of thin films,relationships between physicochemical properties and catalytic performances of thin films,effects of reaction parameters on catalytic performances,durability of thin films,reaction kinetics,mechanisms,DFT modeling and effects of CO₂ under realistic conditions.These investigations give the significant promoting effect of Cu-based TMOs thin films on the combustion aspects,especially for reduction of pollutants emission,improvement of combustion efficiency,and development of low temperature oxidation,which shows potential application at an industrial level.