The Synthesis And Levulinic Acid Hydrogenation Performance Of Ru Catalysts Supported On Sulfur- /Nitrogen-doped Carbon Nanotubes

Carbon nanomaterials have wide applications in catalysis field due to their peculiar structure and excellent physicochemical properties.Heteroatom dopants endow carbon materials interesting electronic characteristics and surface chemistry.In particular,the S-and N-doped carbons have gained a great deal of attention in the last few years.Heteroatom-doped carbon nanotubes(CNTs)exhibit excellent catalytic performance either as metal-free catalysts or as catalyst supports to achieve high dispersion of nobel metals.In this work,we focus on the metal-support interaction of Ru supported on S-doped and N-doped CNTs and evaluate the catalytic performance of the Ru catalyst to understand the relationship between the structure of metal catalysts and the intrinsic activity of levulinic acid hydrogenation reaction.The main contents are as follows:(1)Sulfur-doped CNTs were prepared by thiophene pyrolysis.By changing the prrolysis temperature and using fluorinated CNTs as support,the content of S can be tuned in the range from 0.7% to 6.5%.Ru catalysts were prepared by a homogeneous oxidative deposition method.It was found that the S dopants reduce the activity of supported Ru catalysts in the hydrogenation of levulinic acid,while enhance the stability during a recycling test for five runs.(2)The interaction between Ru NPs and S functional groups was confirmed by the TEM and XPS.Compared with the ordinary CNTs,the active component Ru showed the characteristic of electron deficiency and the electron transferred from Ru to the sulfur-doped carrier.Because the sulfur doping enhanced the interaction between the metal and the support,Ru NPs had smaller particle size and narrower particle size distribution,thus it could stabilize the Ru NPs and improve the stability of the catalyst.(3)Nitrogen doped CNTs were prepared by pyridine pyrolysis.A series of Ru catalysts were prepared by the homogeneous oxidative deposition method.The interaction between specific nitrogen functional groups and Ru NPs on nitrogen doped carbon nanotubes(N@CNT)was systematically studied.Electrons transferred from N@CNT to Ru,revealed by XPS.There is strong interaction between Ru NPs and pyridine nitrogen,where Ru is preferentially anchored.The intrinsic activity of the hydrogenation reaction of levulinic acid is related to the electronic structure of Ru NPs.The Ru catalyst with electron enriched surface has higher intrinsic activity in the hydrogenation of levulinic acid.