| It is known that the volatile organic compounds(VOCs)can cause pronounced damage to the atmospheric environment and the human body.Therefore,how to effectively eliminate VOCs has aroused great attention worldwide.The catalytic combustion is the most effective way to eliminate VOCs.Employing noble metals can improve the low-temperature activity of catalyst.Because of their high price,it cannot be widely used in practical industrial applications.The transition metal oxides show the advantages of low cost and high stability.Loading a small amount of noble metals on the transition metal oxides can not only improve the catalytic activity but also decrease the cost.Morphologically controllable synthesis,element doping,and noble metal loading are common approaches to improve catalyst performance,but the elemental doping in the regularly shaped oxide is rare.Due to different size of metal ions,the formed M-O bond will vary to some extent,leading to local lattice distortion and highly active sites.It is challenging to dope the substrates meanwhile maintain the original facet structure.This thesis focuses on the controllable synthesis of morphologically uniform Co3O4 hexagonal substrate(h-Co3O4),Fe/Mn/Cu elemental doping of h-Co3O4,as well as Pd loading on the distinct substrates.The received materials are applied for toluene catalytic combustion reaction.The following conclusions were derived:1.The Co3O4 hexagonal sheet(h-Co3O4)prepared by hydrothermal method mainly exposes(112)facet.The synthesis process does not use any organic solvent and surfactant.The process is environmental-friendly and free of toxic by-products.The Pd entities of 2-3 nm are successfully loaded on the h-Co3O4 substrate with uniform dispersion,mainly in the form of PdO.Compared to commercial samples,h-Co3O4 and Pd/h-Co3O4 exhibit superior performance of toluene catalytic combustion.Morphological control of the substrate and noble metal loading can greatly enhance the catalytic activity.2.The Fe3O4 and Co3O4 share the spinel structure(AB2O4)characteristics.The Co3O4 hexagonal substrate is doped with Fe in different proportions.A series of morphologically uniform Fe-doped hexagonal substrates(h-FexCo3-xO4,x=0.09,0.14,0.18,0.27)are successfully synthesized.Among them,h-Fe0.14Co2.86O4 outperforms Pd/h-Co3O4 in activity,and Pd/h-Fe0.14Co2.86O4 is the most active among the catalyst serial.3.The Mn3O4 and Co3O4 share the spinel structure(AB2O4)characteristics.The Co3O4 hexagonal substrate is doped with Mn in different proportions.A series of regularly shaped and Mn-doped hexagonal substrates(h-MnxCo3-xO4,x=0.09,0.14,0.18,0.27)are synthesized accordingly.h-Mn0.18Co2.82O4 is close to Pd/h-Fe0.i4Co2.86O4 in activity,and Pd/h-Mn0.18Co2.82O4 is the most active among the series of catalysts.4.Because of the good catalytic combustion performance,a series of regularly shaped and Cu-doped hexagonal substrates(h-CuxCo3-xOn,x=0.09,0.18,0.27)are synthesized.The activity of h-Cu0.18Co2.82On is between that of h-Mn0.18Co2.82O4 and h-Fe0.14Co2.86O4.Pd/h-Cu0.18Co2.82On is found to be the most active in the catalyst serial.5.Various characterizations have been conducted to investigate the surface morphology of sample,the dispersion state and particle size of supported Pd entities,the reduction behavior and reactivity of oxygen species,and the oxidation state and relative content of surface elements.The results indicate that the catalytic performance is highly dependent on the surface vacancy of catalyst and the closely associated oxygen adspecies and its concentration.The oxidation state and surface distribution of Co cations together with the form,oxidation state,and distribution of the doped elements show significant impact on the richness and reactivity of surface oxygen species,and further on the catalytic activity. |
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