Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcin...Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction （XRD）,Raman spectroscopy and X-ray photoelectron spectroscopy （XPS）,among which X-ray diffraction （XRD） was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 （hematite） was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction （TPR） and in situ XRD,which showed the influence of the preparation method.The surface area （BET）,particle size （Rietveld refinement）,as well as surface Ni/Fe atomic ratio （XPS） and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.展开更多
Here, we report on the synthesis of PEG-Mn_3O_4 nanocomposite(NP's) via a hydrothermal route by using Mn(acac)2, ethanol, NH3 and PEG-400. The crystalline phase was identified as Mn_3O_4. The crystallite size of t...Here, we report on the synthesis of PEG-Mn_3O_4 nanocomposite(NP's) via a hydrothermal route by using Mn(acac)2, ethanol, NH3 and PEG-400. The crystalline phase was identified as Mn_3O_4. The crystallite size of the PEG-Mn_3O_4 nanocomposite was calculated as 12±5 nm from X-ray line profile fitting and the average particle size from TEM was obtained as 200 nm. This reveals polycrystalline character of Mn_3O_4 NP's. The interaction between PEG-400 and the Mn_3O_4 NP's was investigated by FTIR. Temperature independent AC conductivity of PEG-Mn_3O_4 nanocomposite beyond 20 k Hz provides a strong evidence of ionic conduction through the structure. The conductivity and permittivity measurements strongly depend on the secondary thermal transition of nanocomposite beyond 100. Above that temperature, Mn_3O_4 particles may interact with each other yielding a percolated path that will facilitate the conduction. On the other hand, the relatively lower activation energy(Ea=0.172 e V) for relaxation process suggests that polymer segmental motions of PEG and electrons hopping between Mn2+and Mn3+may be coupled in the sample below 100. Room temperature magnetization curve of the sample does not reach to a saturation, which indicates the superparamagnetic character of the particles. As the temperature increases, the frequency at which(ε′′) reaches a maximum shifted towards higher frequencies. The maximum peak was observed at 1.4 k Hz for 20 while the maximum was detected at 23.2 k Hz for 90.展开更多
The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of ...The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.展开更多
Peony-like spinel Li4Ti5O12 was synthesized via calcination of precursor at the temperature of 400 ℃, and the precursor was prepared through a hydrothermal process in which the reaction of hydrous titanium oxide with...Peony-like spinel Li4Ti5O12 was synthesized via calcination of precursor at the temperature of 400 ℃, and the precursor was prepared through a hydrothermal process in which the reaction of hydrous titanium oxide with lith- ium hydroxide was conducted at 180 ℃. The as-prepared product was investigated by SEM, TEM and XRD, re- spectively. As anode material for lithium ion battery, the Li4Ti5O12 obtained was also characterized by galvanostatic tests and cyclic voltammetry measurements. It is found that the peony-like Li4Ti5O12 exhibited high rate capability of 119.7 mAh·g ^-1 at 10 C and good capacity retention of 113.8 mAh·g ^-1 after 100 cycles at 5 C, and these results indicate the peony-like Li4Ti5O12 has promising applications for lithium ion batteries with high performance.展开更多
Li x Mn 2O 4 spinels were prepared by in situ redox precipitation hydrothermal synthesis method, and characterized by XRD, BET, TGA, TEM and SEM etc. , and the effects of many factors on the properties of as prepared ...Li x Mn 2O 4 spinels were prepared by in situ redox precipitation hydrothermal synthesis method, and characterized by XRD, BET, TGA, TEM and SEM etc. , and the effects of many factors on the properties of as prepared Li x Mn 2O 4 samples were investigated. The results demonstrated that Li x Mn 2O 4 spinels can be synthesized under milder conditions by in situ redox precipitation hydrothermal synthesis method. Li x Mn 2O 4 spinels are cubic and symmetrical, and have a better stability at less than 700 ℃, their surface areas and particle sizes were strongly affected by crystallization temperature and time, pH value, calcination temperature and time. The optimal conditions of Li x Mn 2O 4 synthesis were determined as follows: the alkalinity(pH value) was 9; the crystallization temperature and time were more than 240 ℃ and 48 h, respectively; the calcination temperature and time were between 700-750 ℃ and 6-12 h, respectively; the molar ratio of Li to Mn was less than 1.2/2.展开更多
文摘Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction （XRD）,Raman spectroscopy and X-ray photoelectron spectroscopy （XPS）,among which X-ray diffraction （XRD） was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 （hematite） was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction （TPR） and in situ XRD,which showed the influence of the preparation method.The surface area （BET）,particle size （Rietveld refinement）,as well as surface Ni/Fe atomic ratio （XPS） and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.
基金the Fatih University,Research Project Foundation(Contract No.:P50020902-2)Turkish Ministry of Industry and TUBITAK(Contract No.:110T487)for financial support of this study
文摘Here, we report on the synthesis of PEG-Mn_3O_4 nanocomposite(NP's) via a hydrothermal route by using Mn(acac)2, ethanol, NH3 and PEG-400. The crystalline phase was identified as Mn_3O_4. The crystallite size of the PEG-Mn_3O_4 nanocomposite was calculated as 12±5 nm from X-ray line profile fitting and the average particle size from TEM was obtained as 200 nm. This reveals polycrystalline character of Mn_3O_4 NP's. The interaction between PEG-400 and the Mn_3O_4 NP's was investigated by FTIR. Temperature independent AC conductivity of PEG-Mn_3O_4 nanocomposite beyond 20 k Hz provides a strong evidence of ionic conduction through the structure. The conductivity and permittivity measurements strongly depend on the secondary thermal transition of nanocomposite beyond 100. Above that temperature, Mn_3O_4 particles may interact with each other yielding a percolated path that will facilitate the conduction. On the other hand, the relatively lower activation energy(Ea=0.172 e V) for relaxation process suggests that polymer segmental motions of PEG and electrons hopping between Mn2+and Mn3+may be coupled in the sample below 100. Room temperature magnetization curve of the sample does not reach to a saturation, which indicates the superparamagnetic character of the particles. As the temperature increases, the frequency at which(ε′′) reaches a maximum shifted towards higher frequencies. The maximum peak was observed at 1.4 k Hz for 20 while the maximum was detected at 23.2 k Hz for 90.
基金Project(2008AA031205)supported by the National High-tech Research and Development Program of China
文摘The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.
文摘Peony-like spinel Li4Ti5O12 was synthesized via calcination of precursor at the temperature of 400 ℃, and the precursor was prepared through a hydrothermal process in which the reaction of hydrous titanium oxide with lith- ium hydroxide was conducted at 180 ℃. The as-prepared product was investigated by SEM, TEM and XRD, re- spectively. As anode material for lithium ion battery, the Li4Ti5O12 obtained was also characterized by galvanostatic tests and cyclic voltammetry measurements. It is found that the peony-like Li4Ti5O12 exhibited high rate capability of 119.7 mAh·g ^-1 at 10 C and good capacity retention of 113.8 mAh·g ^-1 after 100 cycles at 5 C, and these results indicate the peony-like Li4Ti5O12 has promising applications for lithium ion batteries with high performance.
文摘Li x Mn 2O 4 spinels were prepared by in situ redox precipitation hydrothermal synthesis method, and characterized by XRD, BET, TGA, TEM and SEM etc. , and the effects of many factors on the properties of as prepared Li x Mn 2O 4 samples were investigated. The results demonstrated that Li x Mn 2O 4 spinels can be synthesized under milder conditions by in situ redox precipitation hydrothermal synthesis method. Li x Mn 2O 4 spinels are cubic and symmetrical, and have a better stability at less than 700 ℃, their surface areas and particle sizes were strongly affected by crystallization temperature and time, pH value, calcination temperature and time. The optimal conditions of Li x Mn 2O 4 synthesis were determined as follows: the alkalinity(pH value) was 9; the crystallization temperature and time were more than 240 ℃ and 48 h, respectively; the calcination temperature and time were between 700-750 ℃ and 6-12 h, respectively; the molar ratio of Li to Mn was less than 1.2/2.
