Preparation Of Biomass-derived V-based Catalysts And Their Catalytic Oxidation Performances

Catalysts play a very important role in chemical production.According to the literature statistics,about 90%of the chemical reactions are performed in the presence of catalysts.Therefore,the design and development of catalysts with high activity,high selectivity and high stability is a research hotspot in the field of catalysis.In recent years,biomass has attracted more and more attention because of its unique physical and chemical properties.Construction of high-performance heterogeneous catalysts using biomass as precursors has an important industrial application value and academic significance.In this thesis,heterogeneous vanadium-based catalysts V@CN and V-N-C with excellent catalytic performance were prepared by pyrolysis carbonization combined with subsequent acid etching using biomass chitosan as the nitrogen-riched precursor and acetylacetonate oxide(VO(acac)₂)as vavadium metal source,which can effectively improve the nitrogen content and metal dispersion of the developed catalysts.The catalysts were systematically characterized by XRD,TEM,N₂adsorption desorption isotherm,XPS,SEM and HAADF-STEM.The reaction performance of the catalysts was investigated in the selective oxidation of thioethers and the amine-amine and amine-aldehyde oxidation coupling reactions,respectively.The main results are summarized as follows:(1)A biomass-derived carbon material with excellent stability,V@CN-x(x respresent the pyrolysis temperature),was derived by pyrolysis-acid leaching strategy using chitosan as the nitrogen-containing precursor and VO(acac)₂ as the metal precursor,respectively.Under mild reaction conditions,V@CN-700showed a superior catalytic activity compared to the conventional V₂O₅,the VO(acac)₂ homogeneous catalyst and two other vanadium-based catalysts with different pyrolysis temperatures,V@CN-650 and V@CN-850.In addition,the catalytic activity of the V@CN-750 did not decrease significantly after being reused for 8 times,indicating its excellent stability.The excellent catalytic performance of the V@CN-750 is likely originated from the abundant nitrogen dopant and highly dispersed vanadium oxide species within the carbon networks.(2)Based on the experience for the synthesis of V@CN,a heterogeneous vanadium-based catalyst with excellent catalytic activity,V-N-C,was then fabricated by a pyrolysis-acid leaching strategy using chitosan as the sacrificial template,vanadium acetylacetonate as the metal precursor and ZnCl₂ as the activator.The high temperature pyrolysis under N₂ atmosphere resulted in strong coordination between the N species in the support and the metal V,which makes the metal active centre highly dispersed at the atomic level on the N-doped porous carbon skeleton.At the same time,the activation of ZnCl₂ resulted in the V-N-C catalyst with a high specific surface area(1470 m²/g)and pore volume(1.06cm³/g).The highly dispersed active sites and the hierarchically micro-/meso-porous structure render V-N-C better catalytic activity than the commercial V-based catalysts for the amine-amine oxidation coupling reaction.The prepared V-N-C catalysts could be reused for 9 times without any decay in activity,demonstrating its excellent stability.(3)As one of the important nitrogen-containing heterocyclic compounds in organic synthesis,quinazoline compounds display excellent biological and pharmacological activities.Based on the excellent catalytic performance in the oxidative coupling reaction,V-N-C was also applied to the synthesis of2-arylquinazoline compounds by oxidative coupling of amines and aldehydes.As expected,the V-N-C catalyst exhibited excellent catalytic activities.The highly distributed V species in V-N-C make the catalytically active sites fully exposed and thus boosting the reaction.