Preparation And Catalytic Oxidation Properties Of High-dispersed Metal Oxide Nanocatalysts

Phenol and dihydroxybenzenes?DHB?are very important raw material in chemical industry.At present,phenol is mainly produced by cumene method,which broadly constrained by increaseing raw material prices,energy consumption and environmental pollution.Directly hydroxylation of benzene to phenol by using the environmental oxidant of H₂O₂ has become a research hotspot.At the same time,the technology development of directly hydroxylation of phenol to DHB is also currently research focus.Among them,the preparation of highly efficient catalyst is the most important part in the research work.Therefore,it is of great theoretical and practical significance to design and synthesize catalysts with high activity and selectivity for benzene hydroxylation.In this thesis,a series of highly dispersed transition metal oxide nanocatalysts were prepared and loaded on/in the different substrate materials of SBA-16 mesoporous molecular sieves,reduced graphene oxide?RGO?and graphitic carbon nitride?g-C₃N₄?,by using different synthesis strategies on the basis of the structural characteristics of each support material.The synthesized catalysts were fully characterized by various testing methods.The catalytic properties were evaluated by the benzene hydroxylation and phenol hydroxylation for different catalysts.The relationship between the surface species structure and the activity and selectivity of the catalyst was discussed.Cu-SBA-16 mesoporous catalysts were synthesized by evaporation induced self-assembly?EISA?method.The results of structural characterization and activity test indicated that the Cu species were successfully doped into the ordered SBA-16 silica framework,and the doping amount of Cu showed significant effects on the ordered mesoporous structure and catalytic performance.Among various Cu-SBA-16 catalysts,the Cu-S-0.12 well maintained the ordered mesoporous structure of SBA-16,and exhibited the best catalytic performance.The phenol conversion was up to 51.8%,the selectivity of DHB was 77.8%.The isolated Cu2+ ions and highly dispersed Cu O nanoclusters are the main active species for phenol hydroxylation.The Co-SBA-16 catalysts were also prepared by the EISA method.The results of the synthesis and characterizations confirmed that the introduced Co species existed mainly as tetrahedral Co²⁺ ions and isolated Co?II?O4 species in the silica framework and pore surface of SBA-16.The prepared Co-S-0.12 catalyst showed efficient catalytic activity of benzene hydroxylation,the highest benzene conversion of 29.8% with phenol selectivity of 96.6% was obtained.The effects of calcination temperature on the structure and catalytic activity of Co-S-0.12 as well as the reuse of catalyst were also investigated.The VO_x/RGO composite catalysts were prepared by ethanol solvothermal method using GO as precursor with the assistance of CTAB.The microstructure and morphology of VO_x/RGO catalysts were characterized by various testing technology.The VO_x nanoparticles?²5 nm?were highly dispersed on the RGO sheets.The VO_x/RGO was more efficient than individual RGO and V₂O₅ catalysts.The enhanced catalytic performance may be related to not only the well dispersed VO_x active species,but also the hydrophobic surface and huge ?-electron system of RGO for the adsorption and activation of benzene.The effects of calcination conditions on the structure and catalytic properties of VO_x/RGO composite catalysts have also been investigated.The highest phenol yield of 17.4% with the selectivity of 90% was achieved under the optimized catalytic reaction conditions.The transition metal-doped graphitic carbon nitride?M/g-C₃N₄?catalysts were prepared by one-step thermal polycondensation method using dicyandiamide as the precursor.It was focused on the studies of synthesis and catalytic properties of V/g-C₃N₄ materials for benzene hydroxylation.It was found that the V/g-C₃N₄ catalyst exhibited high selectivity to phenol,and the dopped V amount showed important influence on the structure and catalytic properties of V/g-C₃N₄.Amongst,VCN-0.4 gave the highest phenol yield of 14.5%,and selectivity to phenol was up to 98.5%.It can be contributed to not only the structure of g-C₃N₄ with aromatic C-N heterocyclic and conjugated ?-bond,but also the high dispersion of mixed V5+ and V4+ species in the matrix of porous g-C₃N₄ and the synergy between V species and g-C₃N₄.