In this study,Mn_(3)O_(4) spherical particles(SPs)were synthesized by the sol-gel process,after which they were thermally annealed at 400℃,and comprehensively characterized.X-ray Diffraction(XRD)revealed that Mn_(3)O...In this study,Mn_(3)O_(4) spherical particles(SPs)were synthesized by the sol-gel process,after which they were thermally annealed at 400℃,and comprehensively characterized.X-ray Diffraction(XRD)revealed that Mn_(3)O_(4) exhibited a tetragonal spinel structure,and Fourier transformed infrared(FTIR)spectroscopy identified surfaceadsorbed functional groups.Scanning electron microscopy(SEM)and the specific surface area analyses by Brunauer−Emmett−Teller(BET)revealed a porous,homogeneous surface composed of strongly agglomerated spherical grains with an estimated average particle size of∼35 nm,which corresponded to a large specific surface area of∼81.5 m^(2)/g.X-ray photoelectron spectroscopy(XPS)analysis indicated that Mn_(3)O_(4) was composed of metallic cations(Mn^(4+),Mn^(3)+,and Mn^(2+))and oxygen species(O_(2)−,OH−and CO_(3)^(2−)).The optical bandgap energy is∼2.55 eV.Assessment of the catalytic performance of the Mn_(3)O_(4) SPs indicated T90 conversion of CH4 to CO_(2) and H_(2)O at 398℃ for gas hourly space velocity(GHSV)of 72000 mL^(3) g^(−1) h^(−1).This observed performance can be attributed to the cooperative effects of the smallest spherical grain size with a mesoporous structure,which is responsible for the larger specific surface area and available surface-active oxygenated species.The cooperative effect of the good reducibility,higher ratio of active species(OLat/OAds),and results of density functional theory(DFT)calculations suggested that the total oxidation of CH_(4) over the mesoporous Mn_(3)O_(4) SPs might take place via a two-term process in which both the Langmuir−Hinshelwood and Mars−van Krevelen mechanisms are cooperatively involved.展开更多
基金S.K.acknowledges computing time granted by the Center for Computational Sciences and Simulation(CCSS)the Universität DuisburgEssen and provided on the supercomputer magnitude(DFG grants INST 20876/209-1 FUGG,INST 20876/243-1 FUGG)the Zentrum für Informations-und Mediendienste(ZIM).S.K.gratefully acknowledges the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)for funding 388390466-TRR 247.
文摘In this study,Mn_(3)O_(4) spherical particles(SPs)were synthesized by the sol-gel process,after which they were thermally annealed at 400℃,and comprehensively characterized.X-ray Diffraction(XRD)revealed that Mn_(3)O_(4) exhibited a tetragonal spinel structure,and Fourier transformed infrared(FTIR)spectroscopy identified surfaceadsorbed functional groups.Scanning electron microscopy(SEM)and the specific surface area analyses by Brunauer−Emmett−Teller(BET)revealed a porous,homogeneous surface composed of strongly agglomerated spherical grains with an estimated average particle size of∼35 nm,which corresponded to a large specific surface area of∼81.5 m^(2)/g.X-ray photoelectron spectroscopy(XPS)analysis indicated that Mn_(3)O_(4) was composed of metallic cations(Mn^(4+),Mn^(3)+,and Mn^(2+))and oxygen species(O_(2)−,OH−and CO_(3)^(2−)).The optical bandgap energy is∼2.55 eV.Assessment of the catalytic performance of the Mn_(3)O_(4) SPs indicated T90 conversion of CH4 to CO_(2) and H_(2)O at 398℃ for gas hourly space velocity(GHSV)of 72000 mL^(3) g^(−1) h^(−1).This observed performance can be attributed to the cooperative effects of the smallest spherical grain size with a mesoporous structure,which is responsible for the larger specific surface area and available surface-active oxygenated species.The cooperative effect of the good reducibility,higher ratio of active species(OLat/OAds),and results of density functional theory(DFT)calculations suggested that the total oxidation of CH_(4) over the mesoporous Mn_(3)O_(4) SPs might take place via a two-term process in which both the Langmuir−Hinshelwood and Mars−van Krevelen mechanisms are cooperatively involved.
