Co-Mn oxides supported on hierarchical macro-mesoporous silica for CO and VOCs oxidation

The hierarchical macro-mesoporous silica (MMS) was used for a first time as a support for catalysts for oxidation reactions. The macro-mesoporous silica was synthesized by the emulsions templating mechanism and modified separately or simultaneously using cobalt and manganese oxides. The obtained materials were characterized by different physicochemical methods and tested in the oxidation of CO and n-hexane combustion reactions. The modification of the MMS materials does not change significantly the mesopores characteristics; however, its pores are partially blocked by the oxides. For Co-MM sample agglomerates consisting of Co3O4 with average size of 100−150 nm and small spherical aggregates, encapsulated in the mesopores are formed. The amorphous manganese oxide preferentially fills up the mesopores in Mn-MM sample. Mixed oxide Co-Mn phases situated in the mesoporous network are formed in the bi-component Co-Mn samples. No significant change is observed either in the texture, or in the structural features of the catalysts after reaction. The highest catalytic activity for Co-MM sample in CO and n-hexane oxidation is related to the predomination of Co3+ species on the surface of Co3O4 and the more accessible oxide particles located outside the mesopores. The encapsulation of mixed Co-Mn oxides particles in the pores of the macro-mesoporous silica is responsible for a lower catalytic activity in comparison with that of the mono-component cobalt sample

Co3O4-MnOx oxides supported on SBA-15 for CO and VOCs oxidation

International audienceMono-and bi-component cobalt and manganese samples were prepared by ''twosolvent'' technique using SBA-15 as a support. The obtained materials were characterized by SAXS (Small angle X-Ray scattering), N2 adsorption-desorption, X-ray diffraction, TEM (Transmission Electron Microscopy), X-ray photoelectron spectroscopy (XPS), TPR (Temperature-programmed reduction) and O2-TPD (Oxygen Temperature-programmed desorption). The catalytic properties were tested in the complete oxidation of propane, nhexane, and carbon monoxide. The modification of the SBA-15 materials with Co, Mn or simultaneously with both cobalt and manganese does not change significantly the mesoporous structure, however its pores are partially blocked by the oxides, resulting in the decrease in the specific surface area and in the pore volume. In the case of mono component Co-SBA-15, the clusters of Co3O4 are on the surface and they are partially located inside the pore system of SBA-15 while for Mn-SBA-15 sample, the oxide phases preferentially fill up the channels of SBA-15 forming nanowires. The mixed oxide nanowires are formed in the channels of CoMn-SBA-15 material along with small nanoparticles, aggregated outside of the channels. The mesoporous structure and morphology of SBA-15, type of oxide phases and the size of the oxide particles remain almost unchanged after tests in reaction of complete nhexane oxidation and this is valid for all studied samples. The observed resistance towards agglomeration can be attributed to the mesoporous structure. On the other hand, after reaction the surface concentration of different cobalt and manganese species undergoes significant changes, except for the sample with equimolar Co:Mn ratio. The most active catalyst among bi-component Co-Mn samples in all studied reactions, is the catalyst where the Co:Mn molar ratio is 1:0.5, which can be explained by the formation of finely divided oxides, thus ensuring highest reducibility and oxygen mobility

Co3O4-MnOx oxides supported on SBA-15 for CO and VOCs oxidation

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