A Study On Ni-based MOFs: Preparation And The Properties In Catalytic CO Oxidation

Metal-organic frameworks（MOFs）are a kind of crystalline porous materials with high porosity and large specific surface area.which have obtained widespread attention in the catalytic field due to the of high density and uniform active sites,the open channel promoting diffusion of substrate,the high porosity beneficial to the exposure of metal sites,and the easy-functionalized network frameworks.At present,the research about the gas phase CO oxidation catalysis of MOFs usually focuses on the effects of metal clusters or metal nanoparticles on the reaction activity.There are still some problems to be solved in the research of CO catalytic oxidation mechanism.As the diverse types of MOF catalysts have differences in the structures and the reactive sites,the reaction mechanisms are also different.In order to study the relationship between the structure of the catalyst and its catalytic performance,we tested the CO catalytic oxidation activity of different Ni-MOFs materials,and analyzed the differences in their activities through various characterizations.In the first part of this thesis,an organic ligand with two coordination functional groups of pyrazole and carboxylic acid at both ends and an organic ligand with both ends of pyrazole were selected to construct two kinds of reported isostructural Ni-MOFs with different ligand functional groups by coordinating with Ni²⁺.The activity difference of the two catalysts was tested by CO oxidation catalysis reaction,and the detailed analysis of the catalytic difference was conducted by determining the order of reaction and characterizations such as in-situ infrared spectroscopy.This study provides a reference for the influence of the structure of MOFs on the catalytic activity.In the second part,a kind of reported Ni-MOF constructed by a small ligand was pretreated in different atmospheres before CO catalytic oxidation.The CO catalytic oxidation reaction was used to test the difference in the activity of the samples after each atmosphere treatment,and the relationship between the microstructural changes of Ni-MOF and the catalytic activity of CO oxidation was investigated by various characterizations.The research shows that both the ligands and Ni metal clusters of the samples treated with different atmospheres have changed with different degrees,indicating that the microenvironment around the active sites in the MOF has changed after treatment with different atmospheres,and the condition of active sites also was affected at the same time.This work provides a reference for the study of promoting the optimal activity of the material by adjusting the microenvironment around the metal clusters through the pretreatment atmosphere.In the third part,the preliminary exploration of CO selective oxidation and CO₂methanation activity test of Ni-MOFs material was carried out.The test showed that the low CO selectivity and short-term activity for CO2 methanation reaction of the catalysts were the key factor inhibiting the catalytic activity.