Solvent-free Synthesis Of MO_x/ZIF-8 Catalysts And Their Catalytic Performances

Metal-organic frameworks（MOFs）have been extensively applied to construct heterogeneous catalysts,owing to their advantages of clear structure,abundant uniform pore,large surface area and easily tailorable property.Combining MOFs with other catalysts can not only maintain the merits of each components,but also improve the catalytic performance.However,the preparation of MOFs based catalysts often conducts in solvents,the costly and toxic organic solvents are commonly used in order to better dissolve the ligands,which easily causes environmental pollution and does not conform with the idea of green chemisty and sustainable development.In addition,to prepare the composite catalyst constructed by MOFs and low valent metal,the reduction process is usually needed,which is prone to result in collapse of MOFs’framework.It is not benefit for the synthesis of MOF based catalysts and the study of their structure-performance relationship.Based on the background,this thesis developed a green,simple,solvent-free,in situ H₂ reduction method for the preparation of composite catalyst constructed by MOFs and low valent metal,and the detail works are as follows:（1）ZIF-8 is a typical MOF with zeolite-like structure.And noble metal catalysts have been used to catalyze various reactions due to their outstanding catalytic performance.In this work,Zn（OAc）₂ and Pd（OAc）₂ were mixed by ball milling,and the mixture was calcinated in air to produce the Pd O/Zn O.The as-prepared Pd O/Zn O was mixed with 2-methylimidazole by grinding and heated in H₂,and finally the Pd/ZIF-8 composite catalyst was prepared.The structure of Pd/ZIF-8 was characterized by the XRD,XPS,TGA,H₂-TPR,etc.The results revealed that Zn O in Pd O/Zn O almost converted to ZIF-8,and Pd O was reduced to metallic Pd.This developed method can simply operate,does not need any solvents and additional reduction process,and the lost of Pd can be neglected during the synthesis.The Pd/ZIF-8 was used to catalyze the hydrogenation of styrene,it showed a good hydrogenation performance with>99%conversion at 35 ^oC for 12 h under 1atm H₂.（2）Cu based catalysts are commonly used to catalyze various reactions,especially for the Cu catalysts with low valence.By employing the above-mentioned solvent-free synthesis method,this work tries to prepare composite catalyst constructed by MOF and low valent Cu catalyst.Like the preparation of Pd/ZIF-8,CuO and Zn O were mixed by ball milling,and the as-prepared CuO/Zn O was mixed with 2-methylimidazole by grinding and heated in H₂,and finally the CuO_x/ZIF-8（x<1）composite catalyst was prepared.The structure of as-prepared composite catalyst was characterized by XRD,TGA,XPS,AES,etc.,and the results revealed that the Zn O in CuO/Zn O was nearly converted to ZIF-8,and the Cu²⁺was reduced to Cu⁺and Cu⁰.The prepared CuO_x/ZIF-8 was used to catalyze the C-H oxidation,and it exhibits good oxidation performance.