Preparation And Catalytic Properties Of UiO-66 Supported Pt Catalysts

Metal-organic frameworks(MOFs),constructed by metals(metal clusters)and organic ligands,have been considered as a promising class of porous materials.Due to the high porosity,designability and clear structures,MOFs have received great attention in catalysis field.Among the MOF-based catalysts,lots of efforts have been endeavored to develop MOF supported metal catalysts(M/MOFs),owing to their excellent catalytic performance.However,compared to the metal oxide supported metal catalysts,the understanding of M/MOFs is still not enough.In addition,the preparation of MOFs is always carried under the solvothermal conditions.The use of organic solvents increases the production cost of MOFs and causes harmful to environment,which limits the applications of MOFs.Thus,the following works were conducted in this dissertation:(1)Two Pt/UiO-66 catalysts were prepared by impregnation method combined with NaBH4 and H2 reduction,and their catalytic performance for CO oxidation was studied.The influence of reduction method on the structure of the catalyst was analyzed,and the relationship between structure and catalytic performance was clarified.With the reduction of NaBH4 and H2,the obtained Pt/UiO-66 catalysts both contain highly dispersed Pt NP and show high CO oxidation catalytic activity.For the CO oxidation durability test,Pt/UiO-66-NaBH4 exhibits better durability than Pt/UiO-66-H2.The structural analysis shows that the better durability of Pt/UiO-66-NaBH4 is due to its stable structure.Moreover,the stable structure also gives Pt/UiO-66-NaBH4 good water and CO2 tolerance in CO oxidation.In contrast,significant damage to the porous structure and oxidation of Pt species are observed in Pt/UiO-66-H2 during the durability test.In combination with in-situ DRIFTS analysis,the oxidation of Pt species is considered to be the main reason for the poor durability of Pt/UiO-66-H2,rather than the destruction of the porous structure and the formation of carbonate species during the CO oxidation process.In addition,the in-situ DRITFS was used to study the CO oxidation mechanism on the two Pt/UiO-66 catalysts.The results show that Pt/UiO-66-NaBH4 and Pt/UiO-66-H2 follow the Langmuir-Hinshelwood and Mars-van Krevelen mechanisms,respectively.(2)Considering the problemes of solvothermal prepration,we developed a new solvent-free route to prepared UiO-66.In this strategy,the environment-friendly NH4Cl was employed as the template or assistant reagent and mixed with ZrOCl2(H2O)8 and terephthalic acid by simple ball milling.Then,the mixture was transferred to a stainless-steel autoclave and kept at 180? for 24 h to prepare the UiO-66.Compared to the solvothermal preparation,the solvent-free method is simple and environmental-friendly.The structural analysis reveals that the prepared UiO-66 shows a hierarchical porosity and its BET surface area(1491 m2 g-1)is comparable to that of UiO-66 prepared by solvothermal method.In addition,the prepared UiO-66 was used to support Pt nanoparticles(Pt/UiO-66-SF)and applied to catalyze the hydrogenation levulinic acid to ?-valerolactone in aqueous.The results reveal that Pt/UiO-66-SF shows an excellent catalytic performance,the yield of y-valerolactone is approximately 100%in 4 MPa H2 at 110? for 45 min,which is comparable to that of solvothermal prepared UiO-66 supported Pt catalyst.