Synthesisand Catalytic Properties Of Cobalt-based Oxide Nanoarray

Development of structured catalysts （or monolithic catalysts） has beenone of the major achievements in the field of heterogeneous catalysis andchemical reaction engineering recently. Well ordered nanostructured arraywith uniform size and well defined crystal surfaces have promisingapplications in design of novel structured catalysts with high catalytic activity,also are of great importance in the fundamental research of catalysis. Thisdissertation focuses on the studies of cobalt-based oxide nanoarray, regardingthe synthesis and applications in catalysis. With optimization of the synthesisprocess, cobalt-based oxide nanoarray with controlled size and preferentialcrystal surfaces has been fabricated. The catalytic performance of above arraywas performed by probe reactions. The purpose of these studies is toinvestigate the relationship between catalytic activities and microstructures（size/crystal surface） of nanoarray, and to demonstrate the mechanism ofcatalytic process and influencing factors. All these will lead to directionaldesign and synthesis of highly active novel nanoarry structured catalysts,which provides inorganic functional nanomaterials with new solution in the application of catalysis.The details are summarized as follows:Large-scale arrays of hierarchical cobalt iron oxide nanowires withpreferentially exposed reactive crystal planes have been fabricated for use asstructured catalysts, which showed high catalytic activity and excellentcycling stability.. A hydrothermal process involving the formation of a cobaltiron layered double hydroxide （CoFe-LDH） intermediate on an iron substrateenables the subsequent epitaxial growth of cobalt iron hydroxide carbonatenanowires on the LDH nanosheets, and hierarchical cobalt iron oxidenanowire arrays were obtained by subsequent thermal decomposition. Thecobalt iron oxide arrays have a predominance of highly active {11ˉˉ2} planesexposed, and showed high catalytic activity （92.2%conversion） andselectivity （64.6%for benzaldehyde） for styrene oxidation. Furthermore, thecatalysts have excellent recyclability making them a potential material for useas practical structured catalysts.The synthesis of a hierarchical Co₃O₄nanosheet@nanowire arrays（NSWAs） was achieved by facile hydrothermal method and annealingtreatment. The nanosheet@nanowire arrays consists of nickel foam, Co₃O₄nanosheets array and Co₃O₄nanowires array from bottom to top. The growthmechanism of the hierarchical Co₃O₄nanosheet@nanowire arrays was studiedby studying the morphology evolution process upon reaction time. Co₃O₄nanosheets were vertically grown on nickel foam as the secondary structure to form3D framework at nanoscale. Finally, Co₃O₄nanowires grow epitaxiallyalong the nanosheets leads to a three-ordered structure with large surface areaand high porosity. The catalytic performance of Co₃O₄nanosheet@nanowirearrays was performed by styrene oxidation reactions.Co₃O₄nanoarrays with various shapes and sizes on kinds of substrateshave been prepared in hydrothermal synthesis. The influences of concentration,reaction time and temperature on the morphologies of nanoarrays wereinvestigated. SEM and XRD were used to further investigate the crystalstructure and the morphology evolution process upon reaction time.