Preparation Of MOFs-based Multifunctional Catalysts And Its Reaction Performance Of CO₂ With Amine/H₂

Nowadays,global CO2 emissions are increasing year by year,and the CO2 content in the environment is rising day by day,which has caused the greenhouse effect to become more and more serious.The need to reduce the CO2 content in the environment is becoming more and more urgent.By means of catalytic conversion,the content of CO2 in the environment can be effectively reduced,and chemical products with added value can be produced at the same time.Among them,the N-methylation reaction of CO2 with amine and H2 is an important type of reaction in organic synthesis.For this heterogeneous and multi-component reaction,finding an efficient multifunctional catalyst is the key.In this paper,an metal-organic framework MOF-808(Zr)was synthesized by the condensation-reflux method.And the nano-Cu was assembled on MOF-808(Zr)by liquid phase impregnation-reduction method.By changing the amount of Cu salt,Cu/MOF-808(Zr)catalysts with Cu loading of lwt%-5wt%were prepared.In order to increase the acidity of the catalyst,Hf is used instead of Zr.Thus,Cu/MOF-808(Hf)catalysts with Cu loading of 1wt%-5wt%were prepared.The morphology and physical and chemical properties of the catalysts were determined by XRD,SEM,HRTEM,XPS,N2 adsorption-desorption,NH3-TPD and CO2-TPD and other characterization methods.The reaction performance of the catalysts was evaluated by the batch reactor(BR),and the reaction conditions of N-methylation were optimized.Among a series of Cu/MOF-808(Zr)catalysts prepared,4wt%Cu/MOF-808(Zr)has the best reaction performance.Under the optimal conditions,4wt%Cu/MOF-808(Zr)can achieve 64.70%aniline conversion and 54.47%N-methylaniline yield.The characterization results show that 1wt-5wt%Cu/MOF-808(Zr)has the same structure as MOF-808(Zr).Among them,the nano-Cu in 4wt%Cu/MOF-808(Zr)is uniformly distributed on the surface of the regular octahedral MOF crystal,and the average particle size of Cu is 7.1 nm.4wt%Cu/MOF-808(Zr)has 1552.9 m2/g BET specific surface area and mesoporous structure.Cu/MOF-808(Zr)has three weak Lewis acidic sites,one weakly basic site and one moderately basic site.4wt%Cu/MOF-808(Zr)still showed good reaction performance after 3 repeated experiments.In order to improve the acidity of the catalyst,Hf was used instead of Zr to prepare Cu/MOF-808(Hf).By optimizing the conditions,3wt%Cu/MOF-808(Hf)has the best reaction performance under the optimal conditions.Under the optimal conditions,3wt%Cu/MOF-808(Hf)can achieve 62.39%aniline conversion and 57.02%N-methylaniline yield.The characterization results show that 1wt-4wt%Cu/MOF-808(Hf)has the same structure as MOF-808(Hf).Cu/MOF-808(Hf)also has three weak Lewis acidic sites,one weakly basic site and one moderately basic site,and its three weak Lewis acidic sites are stronger than MOF-808(Zr).Cu/MOF-808(Hf)still showed good reaction performance after 3 repeated experiments.