Preparation And Performance Of Highly Efficient Transition Metal Catalysts For Ammonia Decomposition And Propylene Oxidation Reaction

It is well known that transition metal catalysts have excellent physical and chemical properties.Their energy levels contain unpaired electrons,which can be paired with the s/p electrons of the adsorbate,and are susceptible to chemisorption.Moreover,the preparation process of the transition metal catalyst is simple.So transition metal catalyst has a high cost performance and is widely used in many catalytic reactions,such as ammonia decomposition and propene oxidation.The products of NH3 decomposition are pollution-free gas,which do not contain catalytic poisons.Therefore,with the increasing demand for COx-free H2 to supply proton exchange membrane fuel cells,NH3 decomposition reaction has drawn a considerable attention.In this reaction,the catalyst is very important.Transition metal catalysts are cheap,earth-abundant and also exhibit good performance for the reaction.Among many catalysts,molybdenum nitride(Mo2N)is considered to be an ideal catalyst for replacing precious metals,due to their low cost and competitive activities in many hydrogen-related rections.However,there are few reports on bulk Mo2N catalysts which exibit high ammonia decomposition catalytic activity and stability.In addition,the in-depth research work on the structure and catalytic performance of Mo2N catalysts were still insufficient.On the other hand,transition metal catalysts also have significant advantages in catalyzing the oxidation of propene to acrolein.Acrolein is an important organic synthesis intermediate,and it is extremely important in the fine chemical,pharmaceutical and food industries.Among many preparation methods,the partial oxidation of propene method has become the most widely used method because of its atom economy,no pollution to environment.Therefore,this method is of both fundamental and practical importance.At present,much research interest has been attracted to the development of different type of catalyst system for the formation of acrolein,including Ag-based catalyst,Au-based catalyst,and Cu-based catalyst.Among them,as a promising candidate for selective oxidation process,Cu-based catalyst have taken advantages of rich reserves,low cost and high reactivity for activation and conversion of propene for acrolein product.In this thesis,we choose the transition metal(Mo.?Cu)catalysts as the research object.The Mo2N catalyst and the Cu-based catalyst were prepared by a simple method for ammonia decomposition and propene oxidation,respectively.Our aim is to establish the dependence of catalytic activity and stability on the relative synthesis conditions,test conditions and microstructures.It could be further guide the synthesis of catalysts and be helpful to expand the application of transition metal catalysts on other heterogeneous catalysis reactions.The main contents and experimental results of the work are as follows:1.In this work,Mo2N catalysts for ammonia decomposition were successfully synthesized via temperature programmed nitridation of MoO3.A series of characterizations such as XRD,BET and TEM were used to characterize the MoO3 precursors and Mo2N catalysts.The optimal conditions for the synthesis of MoO3 precursors were obtained by using the orthogonal experimental method.Furthermore,were performed to reveal that Mo2N catalyst has good NH3 adsorption ability and facilitate the dissociation adsorption of N2.Moreover,the morphology and structure of Mo2N catalysts well maintained after the reaction.Therefore,our Mo2N catalysts showed very high activity and stability.2.In this work,a series of Cu-WO3 catalysts were synthesized by deposition-precipitation(DP)method to explore the catalytic performance in the selective oxidation of propene to acrolein.The experimental conditions were optimized by orthogonal experiment.We found that when the reaction temperature was 300 ?.,the pretreatment gas was H2,the pH=8 10Cu-WO3 catalyst exhibited best catalytic performance.Compared with the catalyst prepared by the impregnation method and the photodeposition method,the Cu-WO3 catalyst prepared by the DP method exhibited higher propene conversion and acrolein selectivity.At the same time,the Cu-WO3 catalyst exhibited higher acrolein yield than the reported Cu-based catalysts.