Preparation And Co Catalytic Oxidation Performance Of MOFs-derived Co₃O₄

CO oxidation,as a classical probe reaction,has attracted tremendous attentions in the area of fundamental studies.It also has great importance in practical applications,such as air cleanup,gas sensors for the detection,automotive exhaust gas treatment.It has been reported that noble metals and noble-free catalysts are the main catalysts for CO oxidation.Among them,noble metals usually exhibit high activities for CO oxidation.However,the high cost and limited supply constrain their commercial applications.Thus attention has been focused on searching“noble metal-free”catalysts with excellent catalytic properties.Co₃O₄,one kind of the less-expensive alternatives to the noble metals-based catalysts,has been reported to be one of the most efficient catalysts for carbon monoxide oxidation.The composition and shape effects are the key factors to determine the performance of catalysts.Therefore,it is in high value for searching a way to prepare catalysts with controlled compositions and shapes.Recently,metal organic frameworks,with the advantages of tuned compositions and structures,have been extensively applied in the fabrication of function materials with micro/nano structures,such as metal oxides/sulfides/carbides.In this work,metal formate frameworks were used as precursors for investigating the effects of compositions and structures for the catalytic activities towards CO oxidation of Co₃O₄.In the first work,we propose a facial one-step synthesis of bimetallic formate frameworks?[CH₃NH₃][M?HCOO?₃]?M=Co/Cu??Co/Cu-MFFs??and their derivation of ternary oxides Cu_xCo_3-x-x O₄?x=0,0.5,1,1.5?microcubes.The Cu_xCo_3-xO₄ microcubes are constructed by numerous interconnected nanoparticles with uniform distribution of cobalt and copper species.In addition,the Cu/Co atomic ratio can be controlled exactly through adjusting the compositions of the growth precursor solutions.Owing to its larger specific surface area,stronger reducibility and the synergistic effect of two metal oxide components,the mesoporous Cu_xCo_3-x-x O₄with moderate Cu/Co atomic ratio exhibit better performance for CO oxidation reaction than pure Co₃O₄.In the second work,[NH₄][Co?HCOO?₃] polyhedrons and [CH₃NH₃][Co?HCOO?₃]plates were fabricated through changing the kinds of NH₄⁺and the dropping way of ligands in the preparation of MFFs.After calcinating the prepared MFFs with different shapes,Co₃O₄ polyhedrons and Co₃O₄ plates were obtained.When used as catalysts for CO oxidation,Co₃O₄ plates,attaining 100%CO conversion at 85°C,exhibits superior reactivity compared with Co₃O₄ polyhedrons.In addition,Co₃O₄ plates show a good catalytic stability that remains total CO conversion within 24 hours at 90°C.Its good performance can be ascribed to the larger specific surface areas and the richness of Co³⁺on the surface.In the third work,we investigate the potential of[CH₃NH₃][Co?HCOO?₃]as precursors for the preparation of other functional materials,such as hierarchical ZIF-67 and metal oxides.The results indicate that the[CH₃NH₃][Co?HCOO?₃]is a promising template for fabricating other functional materials with unique structures and shapes.In addition,the[CH₃NH₃][Co?HCOO?₃]derived Co₃O₄ nanosheet exhibits good catalytic performance towards CO oxidation.