Preparation Of New Materials Supported Pd-based Catalysts And Application Of Catalytic Performance

A variety of noble metal catalysts including Au?Pt?Ir?Rh and Pd play important roles in catalytic field,recently.Owing to the excellent catalytic activity of the palladium?Pd?-based catalysts,they have been widely used in various reactions such as Suzuki-Miyaura?Heck?oxidation?hydrogenation and dehydrogenation of formic acid.However,homogeneous Pd-based catalysts are difficult to recover and environmental harmful,which limit their industrial applications.Hence,the rational design of heterogeneous Pd-based catalysts is of great significance,which can not only realize the recovering of the catalysts and reduce the cost,but also avoid the leaking of Pd nanoparticles.At present,a variety of materials including activated carbon,organic porous material and metal oxide are demonstrated to be support for Pd nanoparticles.However,most of them exhibit poor catalytic activity.Therefore,it is very important to fabricate new materials that can promote catalytic activity.This dissertation is focus on design and preparation of heterogeneous Pd-based catalysts,which are based on the coordination between Pd?OAc?₂ and-NH₂,and the modification of pyridinic-N and phosphotungstic acid on the electronic structure of Pd nanoparticles.In addition,we also explore the catalytic performance of these heterogeneous Pd-based catalysts in various reactions.The detailed contents are as followed.?1?A facile template-free strategy for the fabrication of organic-inorganic meso-/macro-porous covalent networks was prepared by the combination of the aminopropyl-polyhedral oligomeric silsesquioxanes with terephthalic aldehyde through schiff base chemistry reaction.The different molar ratio of aminopropyl-polyhedral oligomeric silsesquioxanes and terephthalic aldehyde on the material structure and morphology was studied.The obtained materials were fully characterized by CHN elemental analysis,FT-IR,BET,TGA,SEM,EDS,TEM,ICP-AES and XPS.Its catalytic performance for the Suzuki-Miyaura reaction of bromobenzene and phenylboronic acid under water and ethanol as mixed solvent and room temperature conditions was investigated,along with comparisons to various counterparts.The resulting heterogeneous Pd?OAc?₂ catalyst?Pd/POSS-TPA_a?exhibited a high yield of 99%and selectivity of 100%for the Suzuky-Miyaura reaction at room temperature with 30 min.The results demonstrated the BET surface areas and the catalytic activity of these catalysts decreased with the increasing of the usage of terephthalic aldehyde.Besides,-NH₂ groups enhance the catalytic activity of active centers.The catalyst?Pd/POSS-TPA_a?can be easily recycled up to five times without significant loss in the conversion and the leaching of Pd?OAc?₂.The excellent performance of Pd/POSS-TPA_a is mostly attributed to the strong coordination between-NH₂ groups and imine linkage in covalent framework and Pd?OAc?₂.Besides,the high surface and porous structure which can enhance the contact between active centers and reaction substrate more easily also show beneficial effects on catalytic activity.?2?A novel palladium?Pd?-supported nitrogen-doped carbon catalyst?Pd@CN?was prepared via polymerization of 1,3,5-triacryloylhexahydro-1,3,5-triazine?TAT?,adsorption of Pd nanoparticles,and followed by pyrolysis treatment which is based on the regulation of pyridinic-N on the electronic structure of Pd nanoparticles.The obtained catalysts were fully characterized by BET,SEM,TEM,EDS,XRD,XPS and ICP-AES.The catalytic performance of different catalysts for hydrogen production and alkene hydrogenation with formic acid as the carrier was investigated under 90 ^oC condition.Catalytic tests demonstrated that Pd@CN shows superior catalytic activity and selectivity toward the hydrogen production and alkene hydrogenation with formic acid as the carrier.Besides,the catalyst presented improved reusability,structure stability and could be reused five runs without finding significant decrease of activity and obvious leaching of Pd species.Such excellent catalytic performance of Pd@CN is mostly attributed to the prominent surface electronic modulation with pyridinic-N in CN,and the strong interaction of pyridinic-N and Pd avoids the leaching of Pd nanoparticles which is crucial to the reuse of the catalyst.?3?Well-defined crystalline palladium nanoparticles anchored on a phosphotungstic acid?PW?-attached Melem porous hybrid?PW/Melem?were prepared by hybridization of phosphotungstic acid palladium salt and Melem,followed by H₂ reduction method.The obtained catalysts were fully characterized by FT-IR,BET,TGA,XRD,SEM,TEM,HR-TEM,ESR,UV-vis,EDS and ICP-AES,and their catalytic activity for dehydrogenation of formic acid was investigated at 50 ^oC.The target catalyst?Pd/PW/Melem?exhibited extremely high catalytic activity and stable recyclability,achieving high turnover frequency?TOF?of 15393 h^-1 at 50 ^oC for complete FA conversion.The in situ developed PW/Melem support offers strong electron interaction between Pd nanoparticles and PW enabling the resultant catalyst Pd/PW/Melem with a significant enhancement of FA dehydrogenation efficiency.The adsorption of basic-NH₂ groups in Melem to formic acid enhance the contact between Pd nanoparticles and formic acid which is responsible for the excellent catalytic performance of Pd/PW/Melem.Besides,the anchoring effect of PW on Pd nanoparticles and porous catalyst framework enable the catalyst reuse five times without significant loss of catalytic activity and active species.