Preparation Of Pd-based Bimetallic Catalysts And Their Catalytic Performances In The Semi-hydrogenation Of Alkynols

Semi-hydrogenation of alkynols to alkenols is one of the most important and fundamental reactions in fine chemical industry.The chemoselective semihydrogenation of alkynols still remains a challenge owing to the facile overreduction of alkenols to undesired alkyl alcohols.Lindlar catalyst（Pd/Ca CO₃ treated with Pb salts and quinoline）has been widely used industrially but suffers from serious drawbacks including the requirement of a toxic lead salt,the addition of large amount of quinoline to suppress the over-hydrogenation of the product alkenols,which significantly restricts it from wider and new applications.Recently,metal organic frameworks（MOFs）-derived materials have attracted much attention due to the fact that the size,morphology,structure,and other characteristics of pristine MOFs can be partially inherited by virtue of rational design and synthesis.Based on the properties of PS@ZIF-8 and MIL-68（In）,in this thesis,Pd Zn and Pd In bimetallic catalysts were prepared by optimizing the synthesis conditions.The catalysts were systematically characterized by X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and N₂ adsportion isomtherms,and their catalytic performances were evaluated in the selective semihydrogenation of alkynols.The main results were summarized as follows:（1）Pd Zn intermetallic nanoparticles supported on the nitrogen-doped Zn O/carbon hollow spheres（Pd Zn/NCHS@Zn O）as an efficient semihydorgenation catalyst was developed by a conventional wet impregnation and subsequent H₂ reduction method.The prepared Pd Zn/NCHS@Zn O exhibited an excellent catalytic activity and selectivity for the semihydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol.Under mild conditions（45 ^oC,1 atm）,the Pd Zn/NCHS@Zn O catalyst showed a much higher selectivity for 2-methyl-3-buten-2-ol compared to the Pd nanoparticles and Pd Zn/Zn O catalysts.This is mainly due to the electron modulation effect of metal Zn to Pd atom.Moreover,our catalyst was also highly efficient for the semihydrogenation of dehydrolinalool to hydrolinalool,that is a building molecule for the production of vitamin E.This Pd Zn/NCHS@Zn O could be repeatedly used for seven cycles without any significant decrease in activity and selectivity,demonstring its excellent stability.（2）A 0.4%Pd/In-C catalyst was produced by annealing a sacrifice template MIL-68（In）at high temperature and an inert atmosphere,followed by wet impregnation of Pd precursor and subsequent H₂ reduction.Under the condition of 30 ^oC,1 atm of hydrogen pressure,and molar ratio of substrate to Pd being 2100,the 0.4%Pd/In-C catalyst delivered a 99% conversion and a 96%selectivity for the desired alkenol within a duration of 255 min.Moreover,Pd nanoparticles encaged within a MOF MIL-68（In）,Pd@MIL-68（In）,was successfully prepared via one pot direct construction of the MOF framework,cooperative in situ metal precursor incorporation followed by on-site moderate solvothermal process.The composition,structure and morphology of the prepared catalyst were characterized,and their catalytic performance was subsequently investigated in the selective semihydrogenation of 2-methyl-3-butyn-2-ol.At mild reaction conditions（30 ^oC,1 atm of hydrogen pressure）,the Pd@MIL-68（In）bimetallic catalyst was able to achieve 99%conversion of 2-methyl-3-butyn-2-ol in a short time（240 min）and with a 96%selectivity for 2-methyl-3-buten-2-ol.Recycling experiments demonstrated that the 0.4%Pd/In-C and Pd@MIL-68（In）catalysts could be reused for several cycles without significant decrease in activity or selectivity.