| Palladium catalyzed carbonylation reaction has the advantages of good selectivity,excellent atom utilization efficiency,etc.Therefore,palladium catalyzed carbonylation reaction is used as an effective method in the industrial to prepare carbonyl-containing compounds.However,the high temperature and pressure are usually required to promote reaction,which need more sophisticated equipments and higher production costs.Besides,the complex ligands are needed to improve the yield and selectivity of reaction,which will increase the cost for production.Thus,it is very meaningful to build a simple and efficient catalytic system.Based on the interaction between light and matter,photocatalysis and photothermal catalysis have attracted the attention of many researchers.Because of the "earth-abundant" nature,special band structure and high physicochemical stability,graphitic carbon nitride(g-C3N4)is widely studied in many fields as a metal-free and visible-light-responsive photocatalyst.In addition,the electronic effect of the ligand will greatly affect the efficiency of the palladium-catalyzed carbonylation reaction.Since g-C3N4 will generate photo-generated electrons under visible light irradiation,it is expected to replace expensive ligandsIn this paper,g-C3N4 was used as the carrier of palladium metal.The bulk g-C3N4(BCN)was stripped to form g-C3N4 nanosheets(ECN)via the thermal exfoliation.Finally,palladium metal was supported on ECN by microwave-assisted deposition to obtain Pd/ECN.The aberration-corrected scanning transmission electron microscopy(AC-STEM)tests showed that palladium metal was dispersed atomically on the ECN.The characteristic peaks of palladium nanoparticles was not detected by X-ray photoelectron spectroscopy(XPS),which further proved that palladium metal was distributed on ECN at the atomic level.It was found that the recombination efficiency of photogenerated carriers of the palladium-supported catalyst decreased significantly by the tests of photoluminescence(PL)spectroscopy and photocurrent-time experiments.In addition,more photogenerated electrons migrated to the catalyst surface to catalyze the carbonylation reaction.Under the light irradiation,the activity of Pd/ECN in palladium catalyzed carbonylation reaction was tested with iodine benzene was used as a substrate.The results indicated that the yield of methyl benzoate was 77%based on Pd/ECN under the light irradiation with a wavelength of ?400 nm,which was higher than that of the homogeneous catalysts and heterogeneous catalysts commonly used in commercialization.The effects of light and thermal on the reaction were also studied under light irradiation with the different wavelength ranges of light.It was found that the carbonylation reaction based on Pd/ECN was carried out by photothermal catalysis.In addition,the carbonylation reaction based on Pd/ECN was universal when some aryl iodides equipped with different substituents were used as the substrates.In order to further expand the role of g-C3N4 in the reaction system,this paper obtained quasi sphere g-C3N4(s-CN)by the reflow of g-C3N4 nanosheets in the isopropanol.Then,the quasi sphere photocatalyst(Pd@s-CN)was prepared by the microwave-assisted deposition.The scanning electron microscope(SEM)was used to characterize the prepared Pd@s-CN catalyst,which proved that quasi sphere photocatalyst was successfully prepared.The results of transmission electron microscopy(TEM)proved that palladium metal was highly dispersed on the catalyst surface.And through the XPS analysis of Pd@s-CN showed that palladium metal mainly existed on the surface and subsurface of s-CN.The PL and UV-vis diffuse reflection spectra(DRS)were used to characterize the Pd@s-CN,which proved that Pd@s-CN catalyst not only significantly reduced the recombination efficiency of photo-generated carriers but also broadened its visible light absorption range.In this experiment,iodobenzene was used as the substrate to study the catalytic performance of Pd@s-CN in carbonylation reaction under the visible light irradiation to form benzoic acid and benzaldehyde.The results showed that the yield of benzoic acid reached 92%based on Pd@s-CN under the light irradiation with a wavelength of ?400 nm,which was higher than that of the homogeneous catalysts and heterogeneous catalysts commonly used in commercialization.The effects of light and thermal on the reaction were also studied under light irradiation with the different wavelength ranges of light.It was found that the carbonylation reaction based on Pd@s-CN was carried out by photocatalytic mechanism.In this study,Pd/ECN and Pd@s-CN were prepared to catalyze the carbonylation reaction via photothermal catalysis and photocatalysis respectively to making full use of visible light and improve the efficiency of the catalytic reaction.Furthermore,g-C3N4 was used to replace expensive ligands in the reaction.The efficiency of the carbonylation reaction was improved by changing the electronic effect of the ligand.This provides a new idea and method for the palladium catalyzed carbonylation reaction. |
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