Porous cryptomelane-type octahedral molecular sieve(OMS-2)with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC)catalytic elimination.However,complete...Porous cryptomelane-type octahedral molecular sieve(OMS-2)with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC)catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the physicochemical properties of which were extensively characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HR-TEM),B runauer-Emmett-Teller(BET)method,X-ray fluorescence(XRF),X-ray photoelectron spectroscopy(XPS),temperature programmed reduction of H2(H2-TPR),Raman,In situ diffused reflectance infrared Fourier transform spectra(DRIFTS),and density functional theory(DFT)calculations.Results show that the total conversion of toluene can be achieved at 207℃ over PdCe2 with apparent activation energy as low as 62.6 kJ/mol.The strong synergistic effect between Pd and Ce remarkably boosts the catalytic activity of OMS-2,attributed to the abundant Mn^(3+)-O bands and active surface oxygen species.DFT results reveal that oxygen vacancy can be formed over PdCe2 much easily than that of Pd/OMS-2 and Ce/OMS-2 with the oxygen vacancy formation energy of2.42,2.83 and 2.68 eV,respectively.Simply increasing the Pd content cannot promote the catalytic activity although PdO is a critical active center in toluene oxidation.Oxygen vacancy attributed to the integrative effect of Pd,Ce and Mn species plays a promine nt role over prepared catalysts in toluene activation process.The findings reported in this work showed new insights into the designing of highly efficient OMS-2catalysts for VOC deep oxidation by tuning oxygen vacancy concentration.展开更多
Mg-doped manganese oxide octahedral molecular sieve(Mg-OMS-2)catalysts were prepared by hydrothermal method.The photothermal degradation performance of these catalysts for formaldehyde(HCHO)in batch system and continu...Mg-doped manganese oxide octahedral molecular sieve(Mg-OMS-2)catalysts were prepared by hydrothermal method.The photothermal degradation performance of these catalysts for formaldehyde(HCHO)in batch system and continuous system was investigated.The light absorption of OMS-2 was increased by Mg-doped,especially for near infrared light,which promoted surface temperature reach a maximum of 214.8℃ under xenon irradiation.At this temperature,the reinforced surface lattice oxygen and oxygen vacancy that formed by lattice distortion via Mg-doped were activated.The best HCHO elimination efficiency was achieved over Mg_(0.2)/OMS-2 catalyst with Mg^(2+)/Mn^(2+)=1/5,which could reduce HCHO from 250 ppm to 10 ppm within 20 min.The in situ DRIFTS was also carried out to monitor the changes in the content of reaction intermediates and analyze the degradation paths of HCHO.It was found the HCHO was attacked by formed·OH and·O^(2-) to generate formate species and carbonate species,and finally transformed to CO_(2) and H_(2)O.This photothermal catalytic oxidation process exhibited a high efficiency purification of HCHO without the help of extra energy consumption.展开更多
The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South China. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical...The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South China. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical and structural features of the XTM supergene oxide manganese ore. The MnO2 content was over 90%, K2O more than 3%, and water from 2.2%-3.1% which is similar to one in zeolite. The cell parameters of the cryptomelane were given as a0 = 0.9974 nm, b0 = 0.2863 nm, c0 = 0.9693 nm and β91.47(. There was a larger pseduotetragonal tunnel in the natural cryptomelane that was formed by [MnO6] octahedral double chains with aperture of 0.462×0.466 nm2, filled with K cations resulting in some Mn3+ substituting for Mn4+ to balance the negative charges of structure. The finding is important not only for prospecting manganese resources in South China, but also in application of octahedral molecular sieve of natural cryptomelane as that developed in the tetragonal molecular sieve of natural zeolite over the past century. The XTM cryptomelane (OMS-2) may be the real mineral of the active octahedral molecular sieve in nature.展开更多
OMS-2 nanorod catalysts were synthesized by a hydrothermal redox reaction method using Mn SO4（OMS-2-SO4） and Mn（CH3COO）2（OMS-2-AC） as precursors. SO4^2--doped OMS-2-AC catalysts with different SO4^2-concentratio...OMS-2 nanorod catalysts were synthesized by a hydrothermal redox reaction method using Mn SO4（OMS-2-SO4） and Mn（CH3COO）2（OMS-2-AC） as precursors. SO4^2--doped OMS-2-AC catalysts with different SO4^2-concentrations were prepared next by adding（NH4）2SO4solution into OMS-2-AC samples to investigate the effect of the anion SO4^2-on the OMS-2-AC catalyst. All catalysts were then tested for the catalytic oxidation of ethanol. The OMS-2-SO4 catalyst synthesized demonstrated much better activity than OMS-2-AC. The SO4^2-doping greatly influenced the activity of the OMS-2-AC catalyst, with a dramatic promotion of activity for suitable concentration of SO4^2-（SO4/catalyst = 0.5% W/W）. The samples were characterized by X-ray diffraction（XRD）, field emission scanning electron microscopy（FE-SEM）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）,inductively coupled plasma optical emission spectroscopy（ICP-OES）, NH3-TPD and H2-TPR techniques. The results showed that the presence of a suitable amount of SO4^2-species in the OMS-2-AC catalyst could decrease the Mn–O bond strength and also enhance the lattice oxygen and acid site concentrations, which then effectively promoted the catalytic activity of OMS-2-AC toward ethanol oxidation. Thus it was confirmed that the better catalytic performance of OMS-2-SO4 compared to OMS-2-AC is due to the presence of some residual SO4^2-species in OMS-2-SO4 samples.展开更多
基金Project supported by the National Natural Science Foundation of China(21876139,21922606,21407062)the Excellent Youth Foundation of Hubei Province of China(2019CFA078)+1 种基金Outstanding Youth Science and Technology Innovation Team Project for Colleges and Universities of Hubei Province(T2021036)the Hubei Provincial Natural Science Foundation of China(2019CFB578).
文摘Porous cryptomelane-type octahedral molecular sieve(OMS-2)with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC)catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the physicochemical properties of which were extensively characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HR-TEM),B runauer-Emmett-Teller(BET)method,X-ray fluorescence(XRF),X-ray photoelectron spectroscopy(XPS),temperature programmed reduction of H2(H2-TPR),Raman,In situ diffused reflectance infrared Fourier transform spectra(DRIFTS),and density functional theory(DFT)calculations.Results show that the total conversion of toluene can be achieved at 207℃ over PdCe2 with apparent activation energy as low as 62.6 kJ/mol.The strong synergistic effect between Pd and Ce remarkably boosts the catalytic activity of OMS-2,attributed to the abundant Mn^(3+)-O bands and active surface oxygen species.DFT results reveal that oxygen vacancy can be formed over PdCe2 much easily than that of Pd/OMS-2 and Ce/OMS-2 with the oxygen vacancy formation energy of2.42,2.83 and 2.68 eV,respectively.Simply increasing the Pd content cannot promote the catalytic activity although PdO is a critical active center in toluene oxidation.Oxygen vacancy attributed to the integrative effect of Pd,Ce and Mn species plays a promine nt role over prepared catalysts in toluene activation process.The findings reported in this work showed new insights into the designing of highly efficient OMS-2catalysts for VOC deep oxidation by tuning oxygen vacancy concentration.
基金financially supported from the Natural Science Foundation of China(No.51908491)the Ministry of Science and Technology Project of China(No.2017YFE0127400)the Zhejiang Provincial Natural Science Foundation of China(No.LY20B070001)。
文摘Mg-doped manganese oxide octahedral molecular sieve(Mg-OMS-2)catalysts were prepared by hydrothermal method.The photothermal degradation performance of these catalysts for formaldehyde(HCHO)in batch system and continuous system was investigated.The light absorption of OMS-2 was increased by Mg-doped,especially for near infrared light,which promoted surface temperature reach a maximum of 214.8℃ under xenon irradiation.At this temperature,the reinforced surface lattice oxygen and oxygen vacancy that formed by lattice distortion via Mg-doped were activated.The best HCHO elimination efficiency was achieved over Mg_(0.2)/OMS-2 catalyst with Mg^(2+)/Mn^(2+)=1/5,which could reduce HCHO from 250 ppm to 10 ppm within 20 min.The in situ DRIFTS was also carried out to monitor the changes in the content of reaction intermediates and analyze the degradation paths of HCHO.It was found the HCHO was attacked by formed·OH and·O^(2-) to generate formate species and carbonate species,and finally transformed to CO_(2) and H_(2)O.This photothermal catalytic oxidation process exhibited a high efficiency purification of HCHO without the help of extra energy consumption.
基金This work was supported by the National Key Basic Research Program(Grant No.2001CCA02400)the National Natural Science Foundation of China(Grant No.49972017).
文摘The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South China. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical and structural features of the XTM supergene oxide manganese ore. The MnO2 content was over 90%, K2O more than 3%, and water from 2.2%-3.1% which is similar to one in zeolite. The cell parameters of the cryptomelane were given as a0 = 0.9974 nm, b0 = 0.2863 nm, c0 = 0.9693 nm and β91.47(. There was a larger pseduotetragonal tunnel in the natural cryptomelane that was formed by [MnO6] octahedral double chains with aperture of 0.462×0.466 nm2, filled with K cations resulting in some Mn3+ substituting for Mn4+ to balance the negative charges of structure. The finding is important not only for prospecting manganese resources in South China, but also in application of octahedral molecular sieve of natural cryptomelane as that developed in the tetragonal molecular sieve of natural zeolite over the past century. The XTM cryptomelane (OMS-2) may be the real mineral of the active octahedral molecular sieve in nature.
基金financially supported by the National Natural Science Foundation of China (No. 21422706)the Program of the Ministry of Science and Technology of China (No. 2012AA062702)
文摘OMS-2 nanorod catalysts were synthesized by a hydrothermal redox reaction method using Mn SO4（OMS-2-SO4） and Mn（CH3COO）2（OMS-2-AC） as precursors. SO4^2--doped OMS-2-AC catalysts with different SO4^2-concentrations were prepared next by adding（NH4）2SO4solution into OMS-2-AC samples to investigate the effect of the anion SO4^2-on the OMS-2-AC catalyst. All catalysts were then tested for the catalytic oxidation of ethanol. The OMS-2-SO4 catalyst synthesized demonstrated much better activity than OMS-2-AC. The SO4^2-doping greatly influenced the activity of the OMS-2-AC catalyst, with a dramatic promotion of activity for suitable concentration of SO4^2-（SO4/catalyst = 0.5% W/W）. The samples were characterized by X-ray diffraction（XRD）, field emission scanning electron microscopy（FE-SEM）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）,inductively coupled plasma optical emission spectroscopy（ICP-OES）, NH3-TPD and H2-TPR techniques. The results showed that the presence of a suitable amount of SO4^2-species in the OMS-2-AC catalyst could decrease the Mn–O bond strength and also enhance the lattice oxygen and acid site concentrations, which then effectively promoted the catalytic activity of OMS-2-AC toward ethanol oxidation. Thus it was confirmed that the better catalytic performance of OMS-2-SO4 compared to OMS-2-AC is due to the presence of some residual SO4^2-species in OMS-2-SO4 samples.
