| As we know, homogeneous processes are characterized by both high catalytic activity and high selectivity. In turn, homogeneous catalysis has been widely applied in many fields. However, a major obstacle in the further exploitation of homogeneous catalysis has been the perceived inability to easily separate the catalysts from the reaction mixture, which prohibits further recycle use of the catalysts. Furthermore, homogeneous catalysis is expensive and toxic to the environment. In order to overcome these problems, immobilization of the homogeneous catalysis to produce recoverable and recyclable catalysts have been intensively studied. In the last few years, lots of the literatures reported the preparations and catalytic performances of different kinds of heterogeneous catalysts.This thesis concentrates on the preparation of palladium-based heterogenous catalysts under the guidance of31P double quantum filtered Solid State NMR (DQF SSNMR). Furthermore, these catalysts were well characterized, showing detail information of catalysts, which explores the relationship between structure and catalytic performance.1) synthesized a Ph2PCH2CH2-functionalized silica support with ordered mesoporous structure, by P123-surfactant directed co-condensation of Ph2PCH2CH2Si(OEt)3and TEOS. This support could immobilize palladium(Ⅱ) organometallic catalysts by coordinating palladium(Ⅱ) ions with the Ph2P-ligand from Pd(COD)Cl2. This heterogenous catalysts have major characteristics of well order structure and high surface area, which provided scientific basis for high catalytic performance. The31P double-quantum filtered (DQ-filtered) method in solid-state NMR suggested that there existed two coordination mode:palladium coordinates with singel phosphorus (called as Pd-1P) and palladium coordinates two phosphorus (called as Pd-2P). We could also measuring the distance between the two phosphoruses bonded to palladium nucleus. This work provided the basis towards the preparation of pure Pd-2P catalysts.2) We produced two samples, one sample according to the method described in (1), called as Pd-PPh2-R-SBA-15-Y, another sample called as Pd-PPh2-R-SBA-15-con. The Pd-PPh2-R-SBA-15-con can be prepared as follows:synthesize the PdCl2[PPh2(CH2)2Si(OCH2CH3)3]2by DPPTS and Pd(COD)Cl2and then co-condense of PdCl2[PPh2(CH2)2Si(OCH2CH3)3]2and TEOS. Result of31P CP/MAS and DQF SSNMR spectra, suggested the co-existence of both the Pd-2P and the Pd-1P models in Pd-PPh2-R-SBA-15-Y and pure Pd-2P model in Pd-PPh2-R-SBA-15-con. XPS spectra suggested more deficient electron of the Pd-PPh2-R-SBA-15-con than the Pd-PPh2-R-SBA-15-Y. Using Suzuki cross-coupling as a probe to characterize the performance of these two catalysts, we found that Pd-PPh2-R-SBA-15-con had better catalytic performance. Thus our work suggested that Pd-2P coordination model results in better catalytic performance.3) A novel heterogenization method to produce recoverable and recyclable catalysts Pd-CP1is proposed, on the basis of the synthesis technique of metal-organic frameworks (MOF). Pd-CP1can be prepared by coordianting Ph2P-ligand with palladium first and then coordinating with zinc ion to form a MOFs-like structure.31P DQF Solid State NMR suggested that Pd-CP1has pure Pd-2P model while XPS suggested a palladium deficient electronic state. ICP also suggested high load of palladium. Using Sonogashiracross-coupling as a probe to characterize the performance, we found that Pd-CP1had good catalytic performance, which arised from Pd-2P model and Pd deficient electronic state.4) Pd-CP1is an amorphous catalysts without well ordered structure. Thus we synthesized a new catalyst Pd-CP2with well ordered structure through the change of the ligand link structure for the MOF.31P DQF Solid State NMR suggested that Pd-CP2has pure Pd-2P model; FESEM/TEM showed that Pd-CP2have ordered structure with the form of nanorods; XPS suggested a palladium deficient electronic state. Using Sonogashiracross-coupling as a probe to characterize the performance, we found that Pd-CP2also had good catalytic performance... |
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