Design And Synthesis Of Hierarchically Porous Composite Catalysts Based On UiO-66 And The Study Of Catalytic Hydrogenation Performance

Metal-organic frameworks（MOFs）,as a class of porous materials,possess uniform pores,large surface area and diverse commponents,and have been used in various research areas.Among these applications,their catalytic performances have received great attention.However,most of MOFs show microporous structure,the mass transfer of reaction is constrained in these micropores,which is unfavorable for the catalytic performance.To improve the mass transfer,introducing mesopores and macropores into the MOFs to construct the hierarchical MOFs has been regarded as an efficient route.In addition,the hydrogenation reaction is among the important chemical reactions,and nearly 1/4 of reaction involve the hydrogenation step.Thus,the aim of this subject is to construct efficient hydrogenation catalysts using the hierarchical MOFs.UIO-66,a classic MOFs,has the composition of Zr₆O₄（OH）₄（BDC）₆.Due to the strong coordination bonds between the Zr（IV）and the carboxylate ligands,UiO-66exhibits high thermal,chemical and mechanical stability.Therefore,UiO-66 was chosen to design and prepare the efficient hydrogenation catalysts in this study.The specific works are presented as follows:（1）Biomass can not only be an ideal resource to replace traditional fossil energy,but also can be converted into a series of valuable chemicals,which is deeply loved by people.Transition metal phosphide,especially Ni₂P,is a very stable hydrogenation catalyst for biomass conversion.At the same time,the hierarchical MOFs are widely sought after for their abundant and ordered pore channels and excellent mass transfer performance.Therefore,it is of great significance to prepare highly efficient hydrogenation catalyst for biomass conversion by loading Ni₂P on hierarchical MOFs MOFs.However,the studies about metal phosphide MOF composites are still rate,due to the harsh preparation conditions for metal phosphide.In this work,hierarchical UiO-66（HP-UiO-66）was prepared by using the regulator of acetic acid.Then the HP-UiO-66 and Ni（NO₃）₂·6H₂O were mixed via ball milling.Subsequently,the mixture was treated under N₂ at 300 ^oC with sodium hypophosphate as phosphorus source.The final composite was examined by the XRD,BET,XPS and TEM,the results revealed the successful preparation of HP-UiO-66 supported Ni₂P catalyst（HP-Ni₂P-UiO-66）.This loading approach was simple,rapid and didn’t use any solvent,meeting the philosophy of green preparation.In addition,the furfural selective hydrogenation was performed on the HP-Ni₂P-UiO-66.It showed an excellent hydrogenation performance,the conversion of furfural was>95%and the selectivity of cyclopentanone was>95%,under the conditions of 150°C,0.5 MPa H₂ pressure and 10 h.（2）The supported noble metal catalysts are efficiency for the hydrogenation.To prepare the hierarchical MOFs supported noble metal catalysts,the general strategy includes the pre-synthesis of hierarchical MOFs and the loading of noble metal.In this work,we notice that the H₂ spillover is often happened in the supported noble metal catalysts,which can significantly lower the reduction temperatures of redox supports.This means that using the H₂ spillover could reduce the MOFs and destroy their coordination bonds,it may result in defects in MOFs and create hierarchical MOFs.With this in mind,a UiO-66 supported Pd catalyst（Pd-UiO-66）was prepared by using the immersion method with Na BH₄ as the reduction reagent.Then the prepared Pd-UiO-66 catalyst was treated in H₂ atmosphere at different temperature.The obtained composite was characterized by XRD,BET,XPS and TGA,suggesting the successful preparation of hierarchical UiO-66 supported Pd catalyst（HP-Pd-UiO-66）.Finally,the synthesized HP-Pd-UiO-66 catalyst was applied to the hydrogenation of acetophenone.It showed a good hydrogenation activity,the hydrogenation conversion of acetophenone was>99%under the conditions of 60°C,0.5 MPa H₂ and 5 h,which was better than that of Pd-UiO-66.Moreover,the H₂ spillover strategy can also be used to prepare the hierarchical MOF-808 and HKUST-1 supported Pd catalyst.This work provides a new route to prepare hierarchical MOFs.