Preparation Of Noble Metal Nanoclusters Supported On MO₂@CN Derived From NH₂-UiO-66 And Their Catalytic Hydrogenation Performance

Metal-organic frameworks?MOFs?are a class of advanced functional materials formed by self-assembly of metal ions or clusters with organic ligands by coordination.They have been received tremendous attention in the field of heterogeneous catalysis due to their relatively large specific surface area,adjustable pore size,and facile chemical modification.Compared to the conventional catalysts or supports,such as activated carbon and zeolite molecular sieves,the hydrothermal and chemical stabilities of most MOFs are relative low.Considering that MOFs derived materials can partially inherit the properties of parent MOFs,including specific surface area,pore size,morphology,etc.,MOFs materials have been used as sacrificial templates to prepare nanomaterials,such as metal oxides or porous carbons,for energy applications in recent years.However,research on the development of MOFs-derived metal oxide-N-doped porous carbon?CN?as a heterogeneous catalyst support is quite rare.Based-on the features of the composition and structure of hafnium-based?Hf?and zirconium-based?Zr?NH₂-UiO-66 materials,in this master's thesis,we first synthesized MO₂@CN by high-temperature pyrolysis of the parent NH₂-UiO-66?M stands for Hf or Zr?.Subsequently,Ru/HfO₂@CN and Pd/ZrO₂@CN catalysts with high stability were prepared by different methods,and their hydrogenation performance was evaluated in the conversion of biomass-based levulinic acid?LA?to high-value?-valerolactone?GVL?,and 2,3,5-trimethylphenylhydrazine?TMBQ?to a Vitamin E intermediate,2,3,5-trimethylhydroquinone?TMHQ?,respectively.The main results of this master's thesis are summarized as follows:?1?Using the impregnation-reduction method,the Ru nanoclusters were loaded into the support HfO₂@CN derived from NH₂-UiO-66?Hf?to prepare the catalyst Ru/HfO₂@CN,and then it was applied to the liquid-phase hydrogenation of LA to yield GVL.The systematical characterization results indicate that a highly dispersed,nitrogen-doped Ru-based catalyst with porous carbon was prepared while HfO₂ was a mixture of monoclinic and cubic phase.It was found that the LA conversion rate significantly boosted,and a full LA conversion was achieved within a short reaction time of 90 min when Ru/HfO₂@CN was used as the catalyst with H₂O as solvent under a mild reaction condition?80?,1.0 MPa H₂?.And the TOF value could reach1500 h^-1.Moreover,there was no any decay in the activity and selectivity for up to 10consecutive cycles for the developed Ru/HfO₂@CN.In contrast,in the presence of Ru/HfO₂@C?with the support derived from UiO-66?Hf?which without nitrogen-doping?,a much longer reaction time of 180 min was required to reach such a high conversion.The excellent catalytic performance of the Ru/HfO₂@NC catalyst is possibly attributed to the strong acidity of HfO₂ and the anchoring effect of the doped N species on the Ru nanoclusters which promotes the high dispersion and stable existence of Ru.?2?The catalyst precursor Pd@NH₂-UiO-66?Zr?first synthesized by one-pot direct method,and then the target catalyst Pd/ZrO₂@CN was fabricated by pyrolysing the precursor at high temperature in an inert atmosphere.The physicochemical properties of the catalyst was systematically characterized by means of XRD,N₂ adsorption,SEM,TEM,FT-IR,Raman,ICP and XPS techniques and the catalytic performance of Pd/ZrO₂@CN was studied in the hydrogenation of TMBQ to form TMHQ.It was found that the prepared Pd/ZrO₂@CN catalyst could catalyze effectively the hydrogenation of TMBQ to achieve the target product TMHQ with 98%yield as the sole product when the reaction was performed under the reaction condition?110?,1.0 MPa H₂?for 45 min.In addition,the Pd/ZrO₂@CN catalyst also exhibited excellent reusability and no catalyst deactivation occurred even after 5 consecutive cycles.