Synthesis And Catalytic Applications Of Functionalized And Hierarchical Pore MOF-based Composites

Catalysis constitutes a key technology for modern processes in the chemical industry.Heterogeneous catalysis as one of the key links has been widely used in practical production.In spite of significant efforts towards technical innovation in related fields in the past century,the development of novel heterogeneous catalysts is still crucial for specialized applications such as in energy-related catalysis and fine chemistry,especially the application of multifunctional catalysts in tandem catalysis.Due to its advantages of periodic unsaturated metal sites and functionalized organic ligands,metal-organic frameworks（MOFs）have been regarded as one of desirable supports for heterogeneous catalysts over the past two decades.However,the application of MOF in heterogeneous catalysis is still limited by the types of active sites and pore structure,so it is of great significance to design and prepare high-performance MOF based catalysts.In this paper,nanocomposite catalysts were designed and prepared by using metal and MOFs composite,through the regulation of metal nanoparticles and the design of hierarchical pore structure,then obtained a series of achievements in heterogeneous catalysis.The detailed research results are as follows:Firstly,we successfully prepared the multifunctional catalyst Pd@MOF-253 with ultrafine and highly dispersed Pd clusters by using the strong metal-support interaction.The strong electron-donating effect between Pd and MOF and the formation mechanism of amorphous Pd nanoclusters were studied by X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）,solid-state nuclear magnetism（NMR）and other characterization methods and theoretical calculations.The catalytic performance of the multifunctional catalyst in the condensation hydrogenation reaction was further studied by comparative experiments（ultralow loading amount（0.14 wt%）,atmospheric temperature and pressure,its catalytic performance was 4.3 times that of Pd@DUT-5）.Then,the ultra-stable bifunctional catalyst of Pd@MIL-101-SO3 H is successfully constructed and applied in the one-pot oxidation-acetalization reaction whose products have been widely utilized as fuel additives,perfumes,pharmaceuticals and polymer chemistry.Through a series of catalytic experiments,we was verified that the Lewis and Bronsted acid sites could cooperate with Pd to activate the substrate.Then effect of abnormal high water adsorption capacity on the reversible reaction was studied.The results showed that the conversion rate of sulfonated Pd@MIL-101-SO3 H was about 1.5 times than that of Pd@MIL-101.More importantly,Pd@MIL-101-SO3 H is recyclable and can be reused for at least 8 times without sacrificing its catalytic activities,absolutely demonstrating its great potential in practical industrial catalysis.Finally,we propose a simple and general strategy to construct hierarchically porous MOFs through the competitive coordination method using Cu（BF4）2 as both functional sites and etching agents.The resulting MOFs have the in-situ formed defect-mesopores and functional sites without sacrificing the structure stability.The formation mechanism of the defect-mesopores has been explained by a combination of XPS,NMR spectroscopy and first-principle calculation method.This synthetic approach is simple and general which not only can be extended to a variety of stable microporous MOFs,but also can enrich MOFs with versatile functional active sites in the meantime.Compared with the original microporous counterparts,the new hierarchical MOFs exhibit superior adsorption for the bulky dye molecules and the conversion of macromolecular substrates in CO₂ reaction is about 2 times.