Study Of Preparation And Properties Of Catalysts Derived From Metal Organic Frameworks

Metal organic frameworks?MOFs?are a class of ordered porous crystallized materials assembled from metal nodes and organic ligands.They are featured by high surface areas,porousness,varied structure and composition.These features enable MOFs to be ideal precursors for the preparation of carbon,metals,metal compounds and their composite materials,which provides a new direction for the development of catalysts.Catalysts are the key to catalytic technology and the development of efficient and economical catalysts is always the focus of research.In this work,Cu-BTC,Ni-BTC and MIL-96 were selected as precursors to prepare metal-based catalysts for hydrogenation.The physicochemical properties,structural characteristics and catalytic properties of MOFs-derived metal catalysts were explored.The main research contents and results are as follows:?1?Selecting Cu-BTC as the precursor to prepare a series of porous carbon-supported copper-nickel bimetallic catalysts?CuNi@C?with the molar ratio of copper to nickel between0 to 2.5.The prepared catalysts were used for the hydrogenation of furfural aqueous phase rearrangement to cyclopentanone.The effect of the molar ratio of copper to nickel was studied in detail.During the pyrolysis process,the organic ligand in the precursor of MOFs has been converted into an amorphous carbon matrix,which makes the catalysts have high stability.The organic ligand also allivates the agglomeration of metal particles during pyrolysis,resulting in uniformly dispersed nanoscale metal particles.And the formed carbon reduces metal ions to metallic state.CuNi_0.5@C has the best catalytic performance with a specific surface area of91.6 m²·g^-1 and an average nickel particle size of 15 nm,99.3%furfural conversion and 96.9%cyclopentanone yield were obtained under 5 MPa initial hydrogen pressure,130°C and 5 h.?2?CuCo/C bimetallic catalyst was prepared by using Cu-BTC as precursor and used for catalytic hydrogenation of furfural to furfuryl alcohol.The impact of pyrolysis temperature and the molar ratio of cobalt to copper in the range of 0 to 0.5 were investigated.The results show that the addition of the second metal cobalt can alleviate the agglomeration of metal particles during the pyrolysis,and the pyrolysis temperature mainly affects the chemical valence and particle size of metal,morphology and structure of the material.CuCo_0.4/C-600 has the best catalytic performance due to the small metal particle size,the synergy between metal copper,cobalt and cobalt oxide,its high specific surface area and porous structure.The yield of furfuryl alcohol can reach 96.4%at 140°C,3 MPa and 1 h.?3?Ni-BTC doped with trace carbon nanotubes?CNTs?was synthesized as precursor,and porous carbon-supported nickel-based catalyst?Ni@C@CNTs?was obtained by pyrolysis.The addition of CNTs effectively alleviates the agglomeration of nickel and initiates the formation of a new phase Ni₃C during pyrolysis.This transition metal carbide has Pt-like properties and thus has excellent catalytic activity for hydrogenation.In catalytic hydrogenation of furfural to tetrahydrofurfuryl alcohol with Ni@C@CNTs,99.1%furfural conversion and 94.7%tetrahydrofurfuryl alcohol yield can be achieved at 120°C,4 MPa,4 h.?4?Ni-C-Al₂O₃,Ni-C/Al₂O₃,Ni-C and Ni/Al₂O₃ catalysts were prepared by different methods with Ni-BTC and?-Al₂O₃ as precursors and used in conversion of furfuryl alcohol to tetrahydrofurfuryl alcohol.The effect of precursor preparation methods was investigated.The in-situ growth method can effectively disperse Ni-BTC on the surface of Al₂O₃,and the combination of Al₂O₃ and Ni-BTC can further reduce the agglomeration of metal elements during pyrolysis.Due to the small active metal nickel particle size?6.9 nm in average?and the modification of the active site by the carbon matrix,Ni-C-Al₂O₃ catalyst can achieve 99.9%furfuryl alcohol conversion and 98.1%tetrahydrofurfuryl alcohol selectivity at 120°C,0.5 h,4 MPa.?5?MIL-96 was used as the precursor of support to obtain a series of Ni/C-Al₂O₃ catalysts with different nickel loading.In catalytic hydrogenation of furfural to furfuryl alcohol,Ni₁₅/C-Al₂O₃ exhibits the best catalytic performance and excellent stability due to its highly dispersed catalytic active sites,appropriate metal loading,and the interaction of active sites with C-Al₂O₃support.The conversion of furfural was 98.7%and the yield of furfuryl alcohol was 92%at160°C,4MPa and 6 h.However,the specific surface area of Ni₁₅/C-Al₂O₃ is only 37 m²·g^-1and the nickel ions are not completely reduced due to the strong interaction with the support.