The hard-to-remove lattice water has been regarded as a significant obstacle impeding the practical use of Prussian blue analogue cathodes for sodium-ion batteries.This work monitored the electrochemical evolution of ...The hard-to-remove lattice water has been regarded as a significant obstacle impeding the practical use of Prussian blue analogue cathodes for sodium-ion batteries.This work monitored the electrochemical evolution of a hydrated monoclinic sodium manganese hexacyanoferrate cathode by solid-state nuclear magnetic resonance(NMR).For the first time,we established a correlation between the chemical shifts of ^(23)Na NMR signals and the presence or absence of lattice water within this cathode.Through this method,we verified the electrochemical dehydration process that coincides with the merging of two redox platforms and a phase transformation in the initial cycles.Furthermore,we discovered that the lattice water is completely removed after several-day cell rest following a single activation cycle.展开更多
It is highly attractive for the catalysts prepared from renewable materials and/or industrial by-products.Herein,lignosulfonate(LS)as the by-product in the papermaking industry was utilized to fabricate Sn-containing ...It is highly attractive for the catalysts prepared from renewable materials and/or industrial by-products.Herein,lignosulfonate(LS)as the by-product in the papermaking industry was utilized to fabricate Sn-containing organic-inorganic complexing catalysts(Sn(x)@LS)by a simple hydrothermal self-assembly process.The fabricated Sn(x)@LS played an excellent performance in the dehydration of xylose into furfural in the carbon tetrachloride(CTC)-water biphasic system,yielding 78.5%furfural at 180℃for 60 min.It was revealed that strong coordination between Sn4+and the phenolic hydroxyl groups of LS created a robust organic-inorganic skeleton(-Ar-O-Sn-O-Ar-),simultaneously generating potent Lewis acidic sites,and sulfonic acid groups of LS acted as Bronsted acidic sites.Gromacs simulations verified that CTC did not form hydrogen bonds with xylose,which may reduce xylose consumption.The CTC phase effectively extracted furfural,thereby preventing its side reactions throughout the entire process.In addition,Sn(x)@LS exhibited excellent cyclic stability in at least five reaction cycles with only a 5.0% decrease in furfural yield.Thus,this work will give a new window for the catalysts prepared from LS as the industrial by-products in the production of platform chemicals,which is a sustainable chemical conversion process.展开更多
Re-crosslinkable preformed particle gel(RPPG)has been considered to be one of the most promising gels for dealing with fracture and void space conduit(VSC)conformance problems.However,the dehydration of RPPG during it...Re-crosslinkable preformed particle gel(RPPG)has been considered to be one of the most promising gels for dealing with fracture and void space conduit(VSC)conformance problems.However,the dehydration of RPPG during its propagation in the fracture-type features and its effect on gel properties remains unclear.This paper investigates the dehydration behavior during RPPG propagating in an open fracture using matrix-free fracture model.Then the results were verified using real fractured sandstone core model.Moreover,the gel properties after extruding a fracture were studied in detail including gel dehydration and gel strength.Results reveal that the RPPG properties changed significantly with increasing propagation distance,which correlated with the gel injection rate.At high gel injection rates,the dehydration and gel strength(Gʹ)decrease with increasing propagation distance.In contrast,the opposite result was found at low injection rates.Based on the study of the different gel injection rates,it is found that dehydration time is another key factor affecting dehydration behavior.Results also indicate that the fracture width affects gel dehydration at different locations.Dehydration was more pronounced at narrow fractures but only in the inlet section,while in the outlet section,RPPG contains more water than the initial condition.This study has profound implications for field applications.It provides new insights into the transport of RPPG in fractures and helps field engineers to optimize the gel injection operations.展开更多
In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.Th...In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.This study revealed that the use of microwave irradiation to dehydrate Sr(OH)_(2)·8H_(2)O is feasible and surprisingly efficient.The effects of this approach on important parameters were investigated using response surface methodology(RSM).The results revealed that the microwave dehydration process follows a linear polynomial model.In addition,compared with the heating time and material thickness,the microwave-assisted dehydration of Sr(OH)_(2)·8H_(2)O is sensitive to the microwave power and not to the material mass.The relative dehydration percentage reached 99.99%when heated in a microwave oven at 950Wfor just 3 min.In contrast,a relative dehydration percentage of 94.6%was reached when heated in an electric furnace at 180℃for 120 min.The XRD spectra also revealed that most of the Sr(OH)_(2)·8H_(2)O transformed into Sr(OH)_(2)after dehydration via microwave irradiation,whereas a significant portion of the Sr(OH)_(2)·H_(2)O remained after conventional electric dehydration.The experimental data were fitted and analyzed via the thin-layer drying dynamics model,and the results indicated that the dehydrating behavior of Sr(OH)_(2)·8H_(2)O could be well described by the Page model.展开更多
Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstr...Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstructure and strength behavior under different dehydration and rehydration degrees using nuclear magnetic resonance(NMR)and unconfined compressive strength tests.The results showed that the proportion of large-volume biopolymer gel within the sample decreased from 91.91%to 38.28%during dehydration,but increased to 90.44%upon rehydration when sample moisture returned to its original level.The NMR images revealed that biopolymer gel evaporated from outside during the dehydration process,causing the dehydrated biopolymer to shrink and form a high-strength glass,which directly enhanced the soil's macroscopic mechanical properties.Upon rehydration,the biopolymer reabsorbed moisture and gradually expanded,leading to weakened connections between soil particles and a decrease in strength.Therefore,even when the moisture content of soil remained constant during the dehydration and rehydration processes,their unconfined compressive strength(UCS)and failure patterns exhibited significant differences.Both the UCS and NMR signal of biopolymer-treated soil decreased after the first dehydration and rehydration cycle,stabilizing gradually after subsequent cycles.展开更多
The single phase La2（CO3）3·3.4H2 O was synthesized by hydrothermal method. The thermal decomposition and intermediates and final solid products of La2（CO3）3·3.4H2O from 30 to 1000 °C were characteri...The single phase La2（CO3）3·3.4H2 O was synthesized by hydrothermal method. The thermal decomposition and intermediates and final solid products of La2（CO3）3·3.4H2O from 30 to 1000 °C were characterized by XRD, FTIR and DTA-TG. The kinetics of dehydration of La2（CO3）3·3.4H2O in the temperature range of 30-366 °C was investigated under non-isothermal conditions. Flynn-Wall-Ozawa and Friedman isoconversion methods were used to calculate the activation energy and analyze the reaction steps; multivariate non-linear regression program was applied to determine the most probable mechanism and the kinetic parameters. The results show that the thermal dehydration of La2（CO3）3·3.4H2O is a kind of three-step competitive reaction, and controlled by an n-order initial reaction followed by n-order competitive reaction（FnFnFn model）. The activation energy matching with the most probable model is close to value obtained by Friedman method. The fitting curves match the original TG-DTG curves very well.展开更多
The chlorophyll fluorescence kinetics of marine red alga Grateloupia turutunt Yamada, green alga Ulva pertusa Kjellm and brown alga Laminaria japonica Aresch during natural sustained dehydration were monitored and inv...The chlorophyll fluorescence kinetics of marine red alga Grateloupia turutunt Yamada, green alga Ulva pertusa Kjellm and brown alga Laminaria japonica Aresch during natural sustained dehydration were monitored and investigated. The pulse amplified modulation (PAM) system was used to analyze the distinct fluorescence parameters during thallus dehydration. Results proved that the fluorescence kinetics of different seaweed all showed three patterns of transformation with sustained water loss. These were: 1) peak kinetic pattern (at the early stage of dehydration fluorescence enhanced and quenched subsequently, representing a normal physiological state). 2) plateau kinetic pattern (with sustained water loss fluorescence enhanced continuously but quenching became slower, finally reaching its maximum). 3) Platform kinetic pattern (fluorescence fell and the shape of kinetic curve was similar to plateau kinetic pattern). A critical water content (CWC) could be found and defined as the percentage of water content just prior to the fluorescence drop and to be a significant physiological index for evaluation of plant drought tolerance. Once thallus water content became lower than this value the normal peak pattern can not be recovered even through rehydration, indicating an irreversible damage to the thylakoid membrane. The CWC value corresponding to different marine species were varied and negatively correlated with their desiccation tolerance, for example. Laminaria japonica had the highest CWC value (around 90%) and the lowest dehydration tolerance of the three. In addition, a fluorescence 'burst' was found only in red algae during rehydration. The different fluorescence parameters F-o, F-v and F-v, F-m were measured and compared during water loss. Both F-o and F-v increased in the first stage of dehydration but F-v/F-m. kept almost constant. So the immediate response of in vivo chlorophyll fluorescence to dehydration was an enhancement. Later with sustained dehydration F-o increased continuously while F-v decreased and tended to become smaller and smaller. The major changes in fluorescence (including fluorescence drop during dehydration and the burst during rehydration) were all attributed to the change in F-o instead of F-v This significance of F-o indicates that it is necessary to do more research on F-o as well as on its relationship with the state of thylakoid membrane.展开更多
[Objective] The aim was to study on the chlorella resistance to dehydration conditions and effect of different cryoprotecants on drying of chlorella cells.[Method]The protection effect of seven kinds of cryoprotecants...[Objective] The aim was to study on the chlorella resistance to dehydration conditions and effect of different cryoprotecants on drying of chlorella cells.[Method]The protection effect of seven kinds of cryoprotecants on chlorella cells was analyzed.[Result]The protection effect of trehalose on chlorella cells was the best,and the survival rate of chlorella cells had improved by 50% with the applied trehalose concentration of 5%.[Conclusion]The result in this study had important guidance effect on the mutation breeding of chlorella.展开更多
Iron exchanged ZSM-5 with Si/Al ratio from 25 to 300 prepared by three consecutive ion exchanges was used for the dehydration of ethanol to ethylene.The iron exchanged ZSM-5（Si/Al=25） catalyst with an iron content o...Iron exchanged ZSM-5 with Si/Al ratio from 25 to 300 prepared by three consecutive ion exchanges was used for the dehydration of ethanol to ethylene.The iron exchanged ZSM-5（Si/Al=25） catalyst with an iron content of 0.46 wt%gave 97%-99%yield of ethylene at 98%-99%conversion of ethanol at 260℃ and 0.81 h^-1 liquid hourly space velocity.The high performance was maintained for60 d on-stream.X-ray diffraction,Fourier transform infrared spectroscopy of pyridine adsorption,NH3 temperature-programmed desorption and diffuse reflectance UV-vis spectroscopy were used for catalyst characterization.Ion exchange with iron decreased the total acidity of the zeolite,especially the strong acid sites and Bronsted acid sites.The doped iron species were distributed over Fe-ZSM-5 as predominantly isolated Fe^3＋.Therefore,the catalytic performance for ethanol dehydration to ethylene was improved.展开更多
Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）....Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.展开更多
Formic acid （HCOOH） decomposition at Pt film electrode has been studied by electrochem- ical in situ FTIR spectroscopy under attenuated-total-reflection configuration, in order to clarify whether bridge-bonded forma...Formic acid （HCOOH） decomposition at Pt film electrode has been studied by electrochem- ical in situ FTIR spectroscopy under attenuated-total-reflection configuration, in order to clarify whether bridge-bonded formate （HCOOD） is the reactive intermediate for COad for-mation from HCOOH molecules. When switching from HCOOH-free solution to HCOOH- containing solution at constant potential （E=0.4 V vs. RHE）, we found that immediately upon solution switch COad formation rate is the highest, while surface coverage of formate is zero, then after COad formation rate decreases, while formate coverage reaches a steady state coverage quickly within ca. 1 s. Potential step experiment from E=0.75 V to 0.35 V, reveals that formate band intensity drops immediately right after the potential step, while the COad signal develops slowly with time. Both facts indicate that formate is not the reactive intermediate for formic acid dehydration to CO.展开更多
基金supported by grants from the National Natural Science Foundation of China(No.22272055)Scientific and Technological Project of Henan Province(No.222102240081)+1 种基金Science and Technology Planning Project of Anyang City(No.2022C01GX023)the support from Shanghai Synchrotron Radiation Facility(BL14B)for the sXRD experiments.
文摘The hard-to-remove lattice water has been regarded as a significant obstacle impeding the practical use of Prussian blue analogue cathodes for sodium-ion batteries.This work monitored the electrochemical evolution of a hydrated monoclinic sodium manganese hexacyanoferrate cathode by solid-state nuclear magnetic resonance(NMR).For the first time,we established a correlation between the chemical shifts of ^(23)Na NMR signals and the presence or absence of lattice water within this cathode.Through this method,we verified the electrochemical dehydration process that coincides with the merging of two redox platforms and a phase transformation in the initial cycles.Furthermore,we discovered that the lattice water is completely removed after several-day cell rest following a single activation cycle.
基金supported by theNationalNatural Science Foundation of China(No.22361132543)China Postdoctoral Science Foundation(Pre-Station)(No.2023TQ0121)State Key Laboratory of Pulp and Paper Engineering(No.2024ZD05).
文摘It is highly attractive for the catalysts prepared from renewable materials and/or industrial by-products.Herein,lignosulfonate(LS)as the by-product in the papermaking industry was utilized to fabricate Sn-containing organic-inorganic complexing catalysts(Sn(x)@LS)by a simple hydrothermal self-assembly process.The fabricated Sn(x)@LS played an excellent performance in the dehydration of xylose into furfural in the carbon tetrachloride(CTC)-water biphasic system,yielding 78.5%furfural at 180℃for 60 min.It was revealed that strong coordination between Sn4+and the phenolic hydroxyl groups of LS created a robust organic-inorganic skeleton(-Ar-O-Sn-O-Ar-),simultaneously generating potent Lewis acidic sites,and sulfonic acid groups of LS acted as Bronsted acidic sites.Gromacs simulations verified that CTC did not form hydrogen bonds with xylose,which may reduce xylose consumption.The CTC phase effectively extracted furfural,thereby preventing its side reactions throughout the entire process.In addition,Sn(x)@LS exhibited excellent cyclic stability in at least five reaction cycles with only a 5.0% decrease in furfural yield.Thus,this work will give a new window for the catalysts prepared from LS as the industrial by-products in the production of platform chemicals,which is a sustainable chemical conversion process.
文摘Re-crosslinkable preformed particle gel(RPPG)has been considered to be one of the most promising gels for dealing with fracture and void space conduit(VSC)conformance problems.However,the dehydration of RPPG during its propagation in the fracture-type features and its effect on gel properties remains unclear.This paper investigates the dehydration behavior during RPPG propagating in an open fracture using matrix-free fracture model.Then the results were verified using real fractured sandstone core model.Moreover,the gel properties after extruding a fracture were studied in detail including gel dehydration and gel strength.Results reveal that the RPPG properties changed significantly with increasing propagation distance,which correlated with the gel injection rate.At high gel injection rates,the dehydration and gel strength(Gʹ)decrease with increasing propagation distance.In contrast,the opposite result was found at low injection rates.Based on the study of the different gel injection rates,it is found that dehydration time is another key factor affecting dehydration behavior.Results also indicate that the fracture width affects gel dehydration at different locations.Dehydration was more pronounced at narrow fractures but only in the inlet section,while in the outlet section,RPPG contains more water than the initial condition.This study has profound implications for field applications.It provides new insights into the transport of RPPG in fractures and helps field engineers to optimize the gel injection operations.
基金supported by the Research Program of the Science and Technology Department of Guizhou Province(Qiankehe Jichu[2019]1418)the Research Program of Talented Scholars of Guizhou Institute of Technology(XJGC20190965).
文摘In this context,the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate(Sr(OH)_(2)·8H_(2)O)without introducing contaminants.This study revealed that the use of microwave irradiation to dehydrate Sr(OH)_(2)·8H_(2)O is feasible and surprisingly efficient.The effects of this approach on important parameters were investigated using response surface methodology(RSM).The results revealed that the microwave dehydration process follows a linear polynomial model.In addition,compared with the heating time and material thickness,the microwave-assisted dehydration of Sr(OH)_(2)·8H_(2)O is sensitive to the microwave power and not to the material mass.The relative dehydration percentage reached 99.99%when heated in a microwave oven at 950Wfor just 3 min.In contrast,a relative dehydration percentage of 94.6%was reached when heated in an electric furnace at 180℃for 120 min.The XRD spectra also revealed that most of the Sr(OH)_(2)·8H_(2)O transformed into Sr(OH)_(2)after dehydration via microwave irradiation,whereas a significant portion of the Sr(OH)_(2)·H_(2)O remained after conventional electric dehydration.The experimental data were fitted and analyzed via the thin-layer drying dynamics model,and the results indicated that the dehydrating behavior of Sr(OH)_(2)·8H_(2)O could be well described by the Page model.
基金supported by the National Natural Science Foundation of China(Grant No.42102324)the Natural Science Foundation of Hubei Province of China(Grant No.2024AFB686)Open Fund of Badong National Observation and Research Station of Geohazards(Grant No.BNORSG-202102).
文摘Although soil exhibits excellent mechanical performance,the microstructural changes of biopolymer within soil due to dehydration and rehydration are rarely explored.This study aims to explore xanthan gum soil microstructure and strength behavior under different dehydration and rehydration degrees using nuclear magnetic resonance(NMR)and unconfined compressive strength tests.The results showed that the proportion of large-volume biopolymer gel within the sample decreased from 91.91%to 38.28%during dehydration,but increased to 90.44%upon rehydration when sample moisture returned to its original level.The NMR images revealed that biopolymer gel evaporated from outside during the dehydration process,causing the dehydrated biopolymer to shrink and form a high-strength glass,which directly enhanced the soil's macroscopic mechanical properties.Upon rehydration,the biopolymer reabsorbed moisture and gradually expanded,leading to weakened connections between soil particles and a decrease in strength.Therefore,even when the moisture content of soil remained constant during the dehydration and rehydration processes,their unconfined compressive strength(UCS)and failure patterns exhibited significant differences.Both the UCS and NMR signal of biopolymer-treated soil decreased after the first dehydration and rehydration cycle,stabilizing gradually after subsequent cycles.
基金Project(201011005-5)supported by the National Land and Resources Public Welfare Scientific Research Project of ChinaProject(41030426)supported by the National Natural Science Foundation of China+1 种基金Project(20095122110015)supported by Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(2010-32)supported by Scientific Research Foundation of the Education Ministry for Returned Chinese Scholars,China
文摘The single phase La2（CO3）3·3.4H2 O was synthesized by hydrothermal method. The thermal decomposition and intermediates and final solid products of La2（CO3）3·3.4H2O from 30 to 1000 °C were characterized by XRD, FTIR and DTA-TG. The kinetics of dehydration of La2（CO3）3·3.4H2O in the temperature range of 30-366 °C was investigated under non-isothermal conditions. Flynn-Wall-Ozawa and Friedman isoconversion methods were used to calculate the activation energy and analyze the reaction steps; multivariate non-linear regression program was applied to determine the most probable mechanism and the kinetic parameters. The results show that the thermal dehydration of La2（CO3）3·3.4H2O is a kind of three-step competitive reaction, and controlled by an n-order initial reaction followed by n-order competitive reaction（FnFnFn model）. The activation energy matching with the most probable model is close to value obtained by Friedman method. The fitting curves match the original TG-DTG curves very well.
文摘The chlorophyll fluorescence kinetics of marine red alga Grateloupia turutunt Yamada, green alga Ulva pertusa Kjellm and brown alga Laminaria japonica Aresch during natural sustained dehydration were monitored and investigated. The pulse amplified modulation (PAM) system was used to analyze the distinct fluorescence parameters during thallus dehydration. Results proved that the fluorescence kinetics of different seaweed all showed three patterns of transformation with sustained water loss. These were: 1) peak kinetic pattern (at the early stage of dehydration fluorescence enhanced and quenched subsequently, representing a normal physiological state). 2) plateau kinetic pattern (with sustained water loss fluorescence enhanced continuously but quenching became slower, finally reaching its maximum). 3) Platform kinetic pattern (fluorescence fell and the shape of kinetic curve was similar to plateau kinetic pattern). A critical water content (CWC) could be found and defined as the percentage of water content just prior to the fluorescence drop and to be a significant physiological index for evaluation of plant drought tolerance. Once thallus water content became lower than this value the normal peak pattern can not be recovered even through rehydration, indicating an irreversible damage to the thylakoid membrane. The CWC value corresponding to different marine species were varied and negatively correlated with their desiccation tolerance, for example. Laminaria japonica had the highest CWC value (around 90%) and the lowest dehydration tolerance of the three. In addition, a fluorescence 'burst' was found only in red algae during rehydration. The different fluorescence parameters F-o, F-v and F-v, F-m were measured and compared during water loss. Both F-o and F-v increased in the first stage of dehydration but F-v/F-m. kept almost constant. So the immediate response of in vivo chlorophyll fluorescence to dehydration was an enhancement. Later with sustained dehydration F-o increased continuously while F-v decreased and tended to become smaller and smaller. The major changes in fluorescence (including fluorescence drop during dehydration and the burst during rehydration) were all attributed to the change in F-o instead of F-v This significance of F-o indicates that it is necessary to do more research on F-o as well as on its relationship with the state of thylakoid membrane.
基金Support by a Grant from the Major State Basic Research Development Program of China(973 Program,2009CB724702)Science Foundation of Nanjing Industry University(39708010)~~
文摘[Objective] The aim was to study on the chlorella resistance to dehydration conditions and effect of different cryoprotecants on drying of chlorella cells.[Method]The protection effect of seven kinds of cryoprotecants on chlorella cells was analyzed.[Result]The protection effect of trehalose on chlorella cells was the best,and the survival rate of chlorella cells had improved by 50% with the applied trehalose concentration of 5%.[Conclusion]The result in this study had important guidance effect on the mutation breeding of chlorella.
基金supported by the National Natural Science Foundation of China(21376068)the China Postdoctoral Science Foundation(2016M592424)~~
文摘Iron exchanged ZSM-5 with Si/Al ratio from 25 to 300 prepared by three consecutive ion exchanges was used for the dehydration of ethanol to ethylene.The iron exchanged ZSM-5（Si/Al=25） catalyst with an iron content of 0.46 wt%gave 97%-99%yield of ethylene at 98%-99%conversion of ethanol at 260℃ and 0.81 h^-1 liquid hourly space velocity.The high performance was maintained for60 d on-stream.X-ray diffraction,Fourier transform infrared spectroscopy of pyridine adsorption,NH3 temperature-programmed desorption and diffuse reflectance UV-vis spectroscopy were used for catalyst characterization.Ion exchange with iron decreased the total acidity of the zeolite,especially the strong acid sites and Bronsted acid sites.The doped iron species were distributed over Fe-ZSM-5 as predominantly isolated Fe^3＋.Therefore,the catalytic performance for ethanol dehydration to ethylene was improved.
文摘Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.
文摘Formic acid （HCOOH） decomposition at Pt film electrode has been studied by electrochem- ical in situ FTIR spectroscopy under attenuated-total-reflection configuration, in order to clarify whether bridge-bonded formate （HCOOD） is the reactive intermediate for COad for-mation from HCOOH molecules. When switching from HCOOH-free solution to HCOOH- containing solution at constant potential （E=0.4 V vs. RHE）, we found that immediately upon solution switch COad formation rate is the highest, while surface coverage of formate is zero, then after COad formation rate decreases, while formate coverage reaches a steady state coverage quickly within ca. 1 s. Potential step experiment from E=0.75 V to 0.35 V, reveals that formate band intensity drops immediately right after the potential step, while the COad signal develops slowly with time. Both facts indicate that formate is not the reactive intermediate for formic acid dehydration to CO.
