Preparation Of Nitrogen Doped Mesoporous Carbon Supported Transition Metal Nanoparticles And Its Application In Hydrogenation

The introduction of nitrogen heteroatoms or groups in mesoporous carbon could effectively improve the structure and properties of carbon materials,promote the dispersion and stability of the supported transition metal nanoparticles?NPs?,and thus could have favorable impacts on the final catalytic performance of catalysts.In this paper,four nitrogen-doped mesoporous carbon supported transition metal NPs catalysts were designed and synthesized by using different preparation methods,and were applied in different hydrogenation reactions with good catalytic hydrogenation results.?i?The as made rod-like nitrogen-doped ordered mesoporous carbon precursors?as-NOMCs?were prepared through a facial aqueous soft-template self-assembly route in one-pot.After calcination at 800 ^oC under a nitrogen atmosphere,NOMCs with large specific surface area(⁴19 m² g^-1),high pore volume(⁰.33 cm³ g^-1),rich nitrogen content?5.4 wt%?and highly ordered mesostructure were obtained.When rod-like NOMCs were used as the catalyst supports,Pd NPs could be well dispersed on the surface and in the mesopores of the supports?Pd/NOMCs?,possibly owing to the interaction between the Pd NPs and the doped N atoms.Compared with other Pd supported catalysts,Pd/NOMCs exhibited higher catalytic performance for the hydrodechlorination of chlorophenols under mild conditions.?ii?The mesoporous hollow carbon spheres doped with both Fe and N,denoted as Fe-N/C,were prepared using a series of synthetic procedures and silica spheres as the hard templates.Fe-N/C was used as catalyst support to load Pd NPs,and Pd/Fe-N/C was obtained.Under mild reaction conditions?298 K,H₂ 1 atm?,Pd/Fe-N/C showed good catalytic effect for selective hydrogenation of phenylacetylene in liquid phase.A high selectivity towards styrene?higher than 96.2%?was achieved with the total conversion of phenylacetylene within 80 min.The synergistic effects of doped N and Fe with Pd might be important factors on improving the catalytic performance.In addition,the Pd/Fe-N/C could be easily recovered by centrifugation and could still maintain relatively good catalytic activity and selectivity.?iii?Nitrogen doped mesoporous carbon?NC?was prepared by calcining a mixture of melamine and activated carbon at high temperature in an inert atmosphere.NC was used as a catalyst carrier to support iron series element M?M=Fe,Co or Ni?and Pd NPs,and thus Pd-M/NC catalysts were prepared.When applied for the semihydrogenation of phenylacetylene,experimental results showed that the Pd-M/NC exhibited relatively good catalytic performance when the Pd/M content mass ratio was approximately 1:1.The selectivity of styrene could be maintained at a relatively good level even with the prolongation of reaction time.The good catalytic effect of Pd-M/NC may be attributed to the modification of Pd by iron elements and the doping of N,and the possible synergistic effects among them.Through detailed characterization and comparative test of different catalysts,it was found that the modification of Pd by iron series element M and the doping of N had good impacts on the catalytic performance.Moreover,the catalyst could maintain its catalytic activity and selectivity in the recycle process.?iv?Different Co-Ag?n?-MOFs were prepared by introducing Ag into Co based MOFs during the growing process.Then followed the carbothermal reduction process without any additional procedures,we synthesized a series of Co-Ag?n?@NCs.The self-supported catalysts exhibited excellent and stable catalytic effect for the chemoselective hydrogenation of halogenated nitrobenzenes without obvious dehalogenation.Because the Co-Ag bimetal alloy NPs were well-dispersed and protected by the mesoporous nitrogen doped carbon from aggregation and leaching.Besides,either hydrazine hydrate?N₂H₄?H₂O,generate byproducts N₂ and H₂O?or H₂could be used as green reducing agent to provide hydrogen sources.And when the Co/Ag content ratio was about 1:1,the Co-Ag?1:1?@NC showed the best catalytic performance.Moreover,the Co-Ag?1:1?@NC could be efficiently recovered by using an external magnetic force and reused without obvious decrease of catalytic activity.