Design,Sythesis And Catalytic Performance Regulation Of Novel Palladium/Carbon Heterogeneous Nanocatalysts

Pd-based catalysts exhibit unparalleled catalytic performance for the cross-coupling,dehydrogenation and other reactions due to their unique coordination properties and excellent catalytic properties.So,the development of efficient and recyclable heterogeneous palladium catalysts has been an important research field.As one of the most promising supports for heterogeneous palladium catalysts,carbon nanomaterials have attracted great attention owing to their low cost and excellent properties.However,traditional carbon materials supported palladium catalysts suffer from poor catalytic activity and selectivity.Therefore,design and developing highly efficient novel palladium/carbon heterogeneous nanocatalysts are of great significance and application prospects.Surface structure and electronic properties of the supports are the key factors affecting the catalytic performance.Herein,carbon nanomaterials derived from petroleum asphalt was modified by heteroatom doping as potential carriers for the construction of outstanding heterogeneous palladium/carbon catalysts.The main research contents are as follows:Firstly,graphene nanoshell(GNS)samples were prepared by using petroleum asphalt as raw carbon materials and Fe₂O₃ as the template.Nitrogen-doped modification of GNS with urea as the nitrogen source,the doped nitrogen contents and species could be altered by varying the calcination temperature.Pd/N-GNS catalyst was synthesized by a wet chemical reduction for the deposition of palladium nanoparticles(Pd NPs),the catalytic performance of the catalyst which was investigated by N-allylation reaction.Experimental results reveal a strong correlation between the Pd/N-GNS catalytic activity and pyridinic N contents.Particularly,the Pd/N-GNS₈₀₀ exhibited superior catalytic performance,reaching a final TOF of 54.4 h^-1,6.0-fold higher than Pd/GNS₈₀₀ without nitrogen modification.The catalyst could also be recycled for fourth times without activity deterioration.Theoretical studies demonstrate the pyridinic N species are beneficial to reduce the size of Pd NPs and promote the adsorption of Pd NPs and reactants,which effectively promoting the catalytic performance.Secondly,GNS was modified with boric acid as boron source under high temperature.By further deposition Pd NPs to the support,Pd/B-GNS catalyst was prepared toward the dehydrogenation of formic acid(FA).The optimum preparation process of Pd/B-GNS was systematically investigated by adjusting different boric acid mass,doping temperatures and palladium deposition temperatures.The optimal catalyst was prepared by mixing 5-fold mass of boric with GNS,which was further calcined at 900^oC for 2 h under N₂ atmosphere and deposition of Pd NPs at 60^oC.Experimental results showed the improvement of anti-deactivation ability for Pd/B-GNS catalyst,which should be attributed to the promoted interactions between support and palladium via boron doping.The Pd/B-GNS catalyst showed excellent FA dehydrogenation performance,producing 43 m L of gas at 50^oC for 10 min,and no significant activity decrease can be observed after 5 cycles.Finally,high contents nitrogen-doped two-dimensional carbon nanosheets(NSAC)were prepared by an in-suit template method using petroleum asphalt as raw materials and g-C₃N₄ as an intermediate template,the nitrogen content and composition of NSAC could be further adjusted by controlling the calcination temperature.The results reveal well-formed NSAC obtained at a mass ratio of 4:1 of dicyandiamide to petroleum asphalt.Experimental results showed that the pyridinic N species in the supports can effectively promote the transfer of electrons from Pd atoms to carriers,resulting in highly dispersed and stable Pd²⁺like species,which showed remarkable catalytic performance and anti-oxidation property.The Pd/NSAC800showed excellent catalytic properties for Suzuki reaction under Ar atmosphere,reaching a final TOF of 2294.4 h^-1 after five cycles.The catalysts even exhibited higher activity and antioxidant ability in ambient atmosphere,delivering a final TOF of 2800 h^-1 after three cycles.