为研究溶液pH值对微晶纤维素(MC)水热炭化进程、水热炭物理化学特性(产率、固碳率、热值、亲水性、芳香性)及表观形貌的影响规律,MC为原料,以反应溶液pH值分别为3.0、4.0、5.0、6.0、7.0、8.0、9.0、10.0、11.0,在220℃,4 h条件下进行...为研究溶液pH值对微晶纤维素(MC)水热炭化进程、水热炭物理化学特性(产率、固碳率、热值、亲水性、芳香性)及表观形貌的影响规律,MC为原料,以反应溶液pH值分别为3.0、4.0、5.0、6.0、7.0、8.0、9.0、10.0、11.0,在220℃,4 h条件下进行水热炭化实验。通过元素分析pH值对水热炭理化特性的影响,并结合范式图综合分析pH值对MC水热炭化反应进程的影响,利用扫描电子显微镜(SEM)观察水热炭表观形貌。结果表明:水热炭产率和固碳率随酸性的增强而减弱,pH值为3.0时,产率及固碳率最小,分别为35.5%、41.82%,热值达到最大,为19.11 MJ/kg,HC3(hydro-char from pH of 3.0)芳香性最好,HC11(hydro-char from pH of 11.0)亲水性最强,碱性和中性水热炭芳香性、亲水性相似,不同pH值条件下的炭化进程均以脱水反应为主;SEM显示酸性水热炭微球粒径随酸性的增强而减小,纤维素在碱性条件下炭微球粒径均匀度较好。展开更多
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
In order to study their synergistic catalytic effects in toluene degradation, CuMn2O4/HTS-1(HTS-1 was a titanium silicon molecular sieve), Cu0.7Mn2Y0.3Ox/HTS-1 and Cu0.7Mn2Ce0.3Ox/HTS-1 catalysts were prepared by the ...In order to study their synergistic catalytic effects in toluene degradation, CuMn2O4/HTS-1(HTS-1 was a titanium silicon molecular sieve), Cu0.7Mn2Y0.3Ox/HTS-1 and Cu0.7Mn2Ce0.3Ox/HTS-1 catalysts were prepared by the impregnation method.The textural properties, redox properties and acidity of the catalysts were characterized by X-ray diffractometer(XRD),transmission electron microscopy(TEM), scanning electron microscopy(SEM), H2 temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS),frustrated total internal reflection(FT-IR), ammonium temperature-programmed desorption(NH3-TPD) and pyridine adsorption internal reflection(Py-IR) measurements.The potential roles of Lewis acid sites(activating dioxygen) were discussed, and the experimental results indicated that the most efficient route for toluene degradation over Cu0.7Mn2Ce0.3Ox/HTS-1(toluene conversion rate of 90%(T99) = 295℃) was ascribed to regulation of the synergistic effects of redox properties(activating molecular toluene) and Lewis acid sites(activating dioxygen).The Mars–Van–Krevelen(MVK) model was adopted to describe the reaction process of toluene oxidation, which gave an in-depth view into the toluene degradation over CuMn2O4/HTS-1, Cu0.7Mn2Y0.3Ox/HTS-1 and Cu0.7Mn2Ce0.3Ox/HTS-1.In addition, the synergistic effects between redox properties and Lewis acid sites were studied in detail.展开更多
CO oxidation at ceria surfaces has been studied for decades,and many efforts have been devoted to understanding the effect of surface reduction on the catalytic activity.In this work,we theoretically studied the CO ox...CO oxidation at ceria surfaces has been studied for decades,and many efforts have been devoted to understanding the effect of surface reduction on the catalytic activity.In this work,we theoretically studied the CO oxidation on the clean and reduced CeO_(2)(111)surfaces using different surface cells to dete rmine the relationships between the reduction degrees and calculated reaction energetics.It is found that the calculated barrier for the direct reaction between CO and surface lattice O drastically decreases with the increase of surface reduction degree.From electronic analysis,we found that the surface reduction can lead to the occurrence of localized electrons at the surface Ce,which affects the charge distribution at surface O.As the result,the surface O becomes more negatively charged and therefore more active in reacting with CO.This work then suggests that the localized 4 f electron reservoir of Ce can act as the"pseudo-anion"at reduced CeO_(2) surfaces to activate surface lattice O for catalytic oxidative reactions.展开更多
文摘为研究溶液pH值对微晶纤维素(MC)水热炭化进程、水热炭物理化学特性(产率、固碳率、热值、亲水性、芳香性)及表观形貌的影响规律,MC为原料,以反应溶液pH值分别为3.0、4.0、5.0、6.0、7.0、8.0、9.0、10.0、11.0,在220℃,4 h条件下进行水热炭化实验。通过元素分析pH值对水热炭理化特性的影响,并结合范式图综合分析pH值对MC水热炭化反应进程的影响,利用扫描电子显微镜(SEM)观察水热炭表观形貌。结果表明:水热炭产率和固碳率随酸性的增强而减弱,pH值为3.0时,产率及固碳率最小,分别为35.5%、41.82%,热值达到最大,为19.11 MJ/kg,HC3(hydro-char from pH of 3.0)芳香性最好,HC11(hydro-char from pH of 11.0)亲水性最强,碱性和中性水热炭芳香性、亲水性相似,不同pH值条件下的炭化进程均以脱水反应为主;SEM显示酸性水热炭微球粒径随酸性的增强而减小,纤维素在碱性条件下炭微球粒径均匀度较好。
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.
基金supported by the Ministry of Education Blue Fire Program(No.CXZJH201717)Shijiazhuang Science and Technology Department(Nos.181240243A and 191240273A).
文摘In order to study their synergistic catalytic effects in toluene degradation, CuMn2O4/HTS-1(HTS-1 was a titanium silicon molecular sieve), Cu0.7Mn2Y0.3Ox/HTS-1 and Cu0.7Mn2Ce0.3Ox/HTS-1 catalysts were prepared by the impregnation method.The textural properties, redox properties and acidity of the catalysts were characterized by X-ray diffractometer(XRD),transmission electron microscopy(TEM), scanning electron microscopy(SEM), H2 temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS),frustrated total internal reflection(FT-IR), ammonium temperature-programmed desorption(NH3-TPD) and pyridine adsorption internal reflection(Py-IR) measurements.The potential roles of Lewis acid sites(activating dioxygen) were discussed, and the experimental results indicated that the most efficient route for toluene degradation over Cu0.7Mn2Ce0.3Ox/HTS-1(toluene conversion rate of 90%(T99) = 295℃) was ascribed to regulation of the synergistic effects of redox properties(activating molecular toluene) and Lewis acid sites(activating dioxygen).The Mars–Van–Krevelen(MVK) model was adopted to describe the reaction process of toluene oxidation, which gave an in-depth view into the toluene degradation over CuMn2O4/HTS-1, Cu0.7Mn2Y0.3Ox/HTS-1 and Cu0.7Mn2Ce0.3Ox/HTS-1.In addition, the synergistic effects between redox properties and Lewis acid sites were studied in detail.
基金financial support from the National Key R&D Program of China(No.2018YFA0208602)National Natural Science Foundation of China(No.21825301)。
文摘CO oxidation at ceria surfaces has been studied for decades,and many efforts have been devoted to understanding the effect of surface reduction on the catalytic activity.In this work,we theoretically studied the CO oxidation on the clean and reduced CeO_(2)(111)surfaces using different surface cells to dete rmine the relationships between the reduction degrees and calculated reaction energetics.It is found that the calculated barrier for the direct reaction between CO and surface lattice O drastically decreases with the increase of surface reduction degree.From electronic analysis,we found that the surface reduction can lead to the occurrence of localized electrons at the surface Ce,which affects the charge distribution at surface O.As the result,the surface O becomes more negatively charged and therefore more active in reacting with CO.This work then suggests that the localized 4 f electron reservoir of Ce can act as the"pseudo-anion"at reduced CeO_(2) surfaces to activate surface lattice O for catalytic oxidative reactions.
