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
In recent decades,MgSO_(4)·7H_(2)O(epsomite)has attracted significant attention as a promising thermochemical-based thermal energy storage material due to its high theoretical energy density,wide availability,and...In recent decades,MgSO_(4)·7H_(2)O(epsomite)has attracted significant attention as a promising thermochemical-based thermal energy storage material due to its high theoretical energy density,wide availability,and affordability.Despite extensive research efforts,progress in achieving high-energy density has been limited,primarily due to inadequate understanding of its reaction mechanisms and unfavorable dehydration/hydration kinetics.This study systematically investigated the hydration/dehydration kinetics and cyclability of MgSO_(4)·7H_(2)O.The results reveal that the dehydration process is influenced by the heating rate,with an optimal rate of 5℃/min,resulting in a seven-step MgSO_(4)·7H_(2)O dehydration process with a dehydration heat close to the theoretical value.The reaction kinetic analysis indicated that the rate of hydration was approximately 50%lower than that of dehydration.In addition,thermal cycling tests of MgSO_(4)·7H_(2)O under the conditions of this study(small sample size)indicated good cyclability,with hydration rates increasing with increasing cycling numbers up to approximately 10 cycles where level-off occurs.These results are consistent with scanning electron microscopy analyses,which revealed the formation of cracks and channels in the salt hydrate particles,facilitating mass transfer and improved kinetics.展开更多
This paper compares three methods for natural gas dehydration that are widely applied in industry：（1） absorption by triethylene glycol, （2） adsorption on solid desiccants and （3） condensation. A comparison is m...This paper compares three methods for natural gas dehydration that are widely applied in industry：（1） absorption by triethylene glycol, （2） adsorption on solid desiccants and （3） condensation. A comparison is made according to their energy demand and suitability for use. The energy calculations are performed on a model where 105 Nm3/h water saturated natural gas is processed at 30 °C. The pressure of the gas varies from 7 to 20 MPa. The required outlet concentration of water in natural gas is equivalent to the dew point temperature of -10 °C at gas pressure of 4 MPa.展开更多
Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission el...Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction,N2 adsorption-desorption measurement and NH3 temperature-programmed desorption.The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated.Among these catalysts,H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80%methanol conversion and 100%dimethyl ether selectivity in a wide temperature range of 170—300℃,and H-ZSM-5/MCM-41 prepared with nNa/nSi=0.47 showed constant methanol conversion of about 88.7%,100% dimethyl ether selectivity and excellent lifetime at 220℃.The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves.The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.展开更多
A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrime...A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide （CTAB） as templates （samples C and D, respectively）. Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.展开更多
In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim o...In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.展开更多
Phosphoric acid treated niobic acid(NbP)was used for the dehydration of xylose to furfural in biphasic solvent system,which was found to exhibit the best performance among the tested catalysts.The excellent performanc...Phosphoric acid treated niobic acid(NbP)was used for the dehydration of xylose to furfural in biphasic solvent system,which was found to exhibit the best performance among the tested catalysts.The excellent performance of NbP could be explained by the better synergistic cooperation between Bro¨nsted and Lewis acid sites.Moreover,NbP showed good stability and no obvious deactivation or leaching of Nb could be observed after six continuous recycles.展开更多
The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether...The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions （T = 300 ？C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h？1） and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.展开更多
H-ZSM-5 zeolite was synthesized by hydrothermal method. The effects of different synthesis parameters, such as hydrothermal crystallization temperature （170-190 ℃） and Si/A1 molar ratio （100-150）, on the catalyti...H-ZSM-5 zeolite was synthesized by hydrothermal method. The effects of different synthesis parameters, such as hydrothermal crystallization temperature （170-190 ℃） and Si/A1 molar ratio （100-150）, on the catalytic performance of the dehydration of methanol to dimethyl ether （DME） over the synthesized H-ZSM-5 zeolite were studied. The catalysts were characterized by N2 adsorption-desorption, XRD, NH3-TPD, TGA/DTA, and SEM techniques. The full factorial design of experiments was applied to the synthesis of H-ZSM-5 zeolite and the effects of synthesis conditions and their interaction on the yield of DME as the response variable were determined. Analysis of variance showed that two variables and their interaction significantly affected the response. According to the experimental results, the optimized catalyst prepared at 170℃ with the Si/A1 molar ratio of 100 showed the best catalytic performance among the tested H-ZSM-5 zeolite.展开更多
Phosphorylated mesoporous carbons （PMCs） were investigated as catalysts in the dehydration of fructose to hydroxymethylfurfural （HMF）. The acidic PMCs show better selectivity to HMF compared to sulfonated carbon c...Phosphorylated mesoporous carbons （PMCs） were investigated as catalysts in the dehydration of fructose to hydroxymethylfurfural （HMF）. The acidic PMCs show better selectivity to HMF compared to sulfonated carbon catalyst （SC） despite lower activity. The concentration of P-O groups on the PMC was correlated with the activity/selectivity of the catalysts; the higher the P-O concentration, the higher the activity. However, the higher the P-O content, the lower the selectivity to HME Indeed, a lower concentration of the P-O groups minimized the degradation of HMF to levulinic acid and the formation of by-products, such as humines. Stability tests showed that these systems deactivate due to the formation of humines and water insoluble by-products derived from the dehydration of fructose which blocked the catalytically active sites.展开更多
In this research, the influence of several factors such as reaction time, catalyst weight, temperature and different solvents on dehydration reaction of fructose and glucose to 5-hydroxymethylfurfural（HMF） was surve...In this research, the influence of several factors such as reaction time, catalyst weight, temperature and different solvents on dehydration reaction of fructose and glucose to 5-hydroxymethylfurfural（HMF） was surveyed. Nanosphere Al-KCC-1 silica with fibrous morphology was manufactured and used as proficient and recyclable catalyst for this reaction. SEM, TEM, BET, XRD, EDX, elemental mapping, ICP and FT-IR spectroscopy methods were applied for characterization of the Al-KCC-1（molar ratio Si/Al = 5, 40） catalysts. 162℃ and 1 h are the best conditions for the fructose dehydration. Under this situation HMF yield and selectivity are 92.9% and 94.5% respectively and fructose conversion is 98.4%. Also 170℃ and 2 h are the best conditions for the glucose dehydration. In this situation HMF yield and selectivity are 39.0% and39.9% respectively and glucose conversion is 97.8%.展开更多
The main challenge in the dehydration of glycerol to acrolein lies in overcoming catalystdeactivation and improving the selectivity to acrolein. The relationship between theacidity in the mesoporous channels and catal...The main challenge in the dehydration of glycerol to acrolein lies in overcoming catalystdeactivation and improving the selectivity to acrolein. The relationship between theacidity in the mesoporous channels and catalytic performance of glycerol dehydration israrely reported. In this work, to investigate the influence of acidity in the mesoporouschannels of hierarchical ZSM-5 catalysts on the dehydration of glycerol to acrolein, a seriesof hierarchical ZSM-5 zeolites with comparable mesoporous volume and mesoporous sizebut different acid properties in mesopores have been successfully prepared via alkalinetreatment. The sample with the abundant mesoporosity and highest acidity display thebest performance.展开更多
Factors influencing dehydration of xylose to furfural,such as catalyst and extract agents,were investigated.Results indicated that high-temperature water may substitute for solid and liquid acid as a catalyst,and ethy...Factors influencing dehydration of xylose to furfural,such as catalyst and extract agents,were investigated.Results indicated that high-temperature water may substitute for solid and liquid acid as a catalyst,and ethyl butyrate improved furfural yield for the high distribution coefficient.A furfural yield of 75 % was obtained at200 °C for 3 h in ethyl butyrate/water.The reaction kinetics of xylose dehydration to furfural was investigated and it was found that the reaction order was 0.5,and the activation energy was 68.5 k J/mol.The rate constant k showed a clear agreement with the Arrhenius law from160 to 200 °C.展开更多
The catalytic conversion of methanol to dimethyl ether(DME) over a series of home-made FER-type zeolites having different acidities and commercial γ-Al_2O_3 has been studied with the aim to understand the impact of a...The catalytic conversion of methanol to dimethyl ether(DME) over a series of home-made FER-type zeolites having different acidities and commercial γ-Al_2O_3 has been studied with the aim to understand the impact of adding water in the reactant stream on the catalytic behavior on investigated materials. Cofeeding water with methanol, the alcohol conversion was slightly reduced over the investigated zeolites while the catalytic activity of γ-Al_2O_3, the traditional catalyst of MeOH-to-DME conversion, was strongly inhibited. It was also found that, for the investigated zeolites, both the amount and the initial deposition rate of the coke formed during the reaction were reduced when water was co-fed with methanol while no significant effects on both methanol conversion and DME selectivity were observed under the investigated conditions.展开更多
A serial of protonated and layered transition metal oxides, including layered HTaWO6, HNbMoO6 as well as HNbWO6, were synthesized by solid-state reaction and ion-exchange. The layered HTaWO6 has been systematically st...A serial of protonated and layered transition metal oxides, including layered HTaWO6, HNbMoO6 as well as HNbWO6, were synthesized by solid-state reaction and ion-exchange. The layered HTaWO6 has been systematically studied as a solid acid to realize the dehydration of fructose to 5-hydroxymethylfurfural (HMF). The transition metal oxide samples were characterized with ICP-OES, EDS, XRD, XPS, SEM, TGA, FT-IR, N-2 adsorption-desorption and NH3-TPD. The influential factors such as reaction temperature, reaction time, solvent, catalyst amount and substrate concentration were deeply investigated. The optimized fructose conversion rate of 99% with HMF yield of 67% were achieved after 30 min at 140 degrees C in dimethylsulfoxide. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.展开更多
BACKGROUND: Dehydration and its associated symptoms are among the most common chief complaints of children in rural Panama. Previous studies have shown that intravascular volume correlates to the ratio of the diameter...BACKGROUND: Dehydration and its associated symptoms are among the most common chief complaints of children in rural Panama. Previous studies have shown that intravascular volume correlates to the ratio of the diameters of the inferior vena cava(IVC) to the aorta(Ao). Our study aims to determine if medical students can detect pediatric dehydration using ultrasound on patients in rural Panama. METHODS: This was a prospective, observational study conducted in the Bocas del Toro region of rural Panama. Children between the ages of 1 to 15 years presenting with diarrhea, vomiting, or parasitic infection were enrolled in the study. Ultrasound measurements of the diameters of the IVC and abdominal aorta were taken to assess for dehydration. RESULTS: A total of 59 patients were enrolled in this study. Twenty-four patients were clinically diagnosed with dehydration and 35 were classified to have normal hydration status. Of the 24 patients with dehydration, half(n=12) of these patients had an IVC/Ao ratio below the American threshold of 0.8. Of the remaining asymptomatic subjects, about half(n=18) of these subjects also had an IVC/Ao ratio below the American threshold of 0.8.CONCLUSION: Our study did not support previous literature showing that the IVC/Ao ratio is lower in children with dehydration. It is possible that the American standard for evaluating clinical dehydration is not compatible with the rural pediatric populations of Panama.展开更多
In this paper, microscopic characteristics of preformed gels （PGs） and secondary cross-linked gels （SCG） with the same concentration were analyzed by atomic force microscopy （AFM）. Experimental results indicate ...In this paper, microscopic characteristics of preformed gels （PGs） and secondary cross-linked gels （SCG） with the same concentration were analyzed by atomic force microscopy （AFM）. Experimental results indicate that the microstructure of secondary cross-linked gels is a thick 3-D network, in which micro-holes and irregular macro-holes are embedded. The maximum width of the irregular macro-holes is 200 nm. In the SCG two different chemical bonds were formed, which leads to the structural inhomogeneity and the asymmetry of the crosslinking density. The structural inhomogeneity of SCG results in the formation of irregular macro-holes. The excessive cross-linking density is the primary reason for dehydration of SCG and the presence of irregular macro-holes in SCG can facilitate dehydration.展开更多
A study on catalytic dehydration of 4-hydroxy-3-hexanone （HH） to 4-hexen-3-one （HO） was carried out through conversion of HH over HZSM-5 zeolite catalyst in a fixed-bed reactor （FBR） operating under almospheric ...A study on catalytic dehydration of 4-hydroxy-3-hexanone （HH） to 4-hexen-3-one （HO） was carried out through conversion of HH over HZSM-5 zeolite catalyst in a fixed-bed reactor （FBR） operating under almospheric pressure. The test indicated a relatively high activity of the HZSM-5 zeolite capable of achieving a HH conversion of 99.2% and a HO yield of 83.5%. Catalyst deactivation could be prevented by increasing the reaction temperature by 10 ＂C for every 20 h and adding 2.0% of piperidine in the feed. A catalyst stability test （for 100 h） in FBR showed that the catalyst was active even after 100 h of time-on-stream with HH conversion remaining at 99.2% and HO yield still reaching over 83.5%. Regenera- tion experiment showed that the regenerated catalyst demonstrated a catalytic performance comparable to the fresh one.展开更多
The V-P/HZSM-5 catalyst was prepared by impregnation method using HZSM-5 zeolite as the carrier.Its catalytic activity was examined on dehydration of bio-ethanol in a self-designed fluidized bed reactor to manufacture...The V-P/HZSM-5 catalyst was prepared by impregnation method using HZSM-5 zeolite as the carrier.Its catalytic activity was examined on dehydration of bio-ethanol in a self-designed fluidized bed reactor to manufacture ethylene. The effects of dehydration conditions on catalytic behaviors were investigated.The results showed that the V-P/HZSM-5 catalyst demonstrated good activity for bio-ethanol dehydration.Both bio-ethanol conversion and ethylene selectivity were over 90%under the following reaction conditions:a P/V atomic ratio of 7.5,a catahst calcination temperature of 300℃,a reaction temperature of 220℃,a bio-ethanol flow rate of 0.1 mL/min.and a catalyst dosage of 3.0 g.Furthermore,the catalyst exhibited excellent catalytic stability and regeneration capability.展开更多
A Zn-BDC(1,4-benzene-dicarboxylic acid)compound has been studied herein during reversibly adsorbing and desorbing water from a dimethyl formamide(DMF)solvent.The compound is structurally stable and can be reused.XRD,T...A Zn-BDC(1,4-benzene-dicarboxylic acid)compound has been studied herein during reversibly adsorbing and desorbing water from a dimethyl formamide(DMF)solvent.The compound is structurally stable and can be reused.XRD,TG,SEM,and BET results show that the morphology,textural properties and phase can gradually transform from a non-porous compound into a porous Zn-MOF by being exposed in the steam of DMF with trace water.This dried phase[Zn(BDC)]is able to reversibly remove/uptake coordinating water molecules,which can provide Zn-BDC compound with the ability to dehydrate the solvent.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.
文摘In recent decades,MgSO_(4)·7H_(2)O(epsomite)has attracted significant attention as a promising thermochemical-based thermal energy storage material due to its high theoretical energy density,wide availability,and affordability.Despite extensive research efforts,progress in achieving high-energy density has been limited,primarily due to inadequate understanding of its reaction mechanisms and unfavorable dehydration/hydration kinetics.This study systematically investigated the hydration/dehydration kinetics and cyclability of MgSO_(4)·7H_(2)O.The results reveal that the dehydration process is influenced by the heating rate,with an optimal rate of 5℃/min,resulting in a seven-step MgSO_(4)·7H_(2)O dehydration process with a dehydration heat close to the theoretical value.The reaction kinetic analysis indicated that the rate of hydration was approximately 50%lower than that of dehydration.In addition,thermal cycling tests of MgSO_(4)·7H_(2)O under the conditions of this study(small sample size)indicated good cyclability,with hydration rates increasing with increasing cycling numbers up to approximately 10 cycles where level-off occurs.These results are consistent with scanning electron microscopy analyses,which revealed the formation of cracks and channels in the salt hydrate particles,facilitating mass transfer and improved kinetics.
基金supported by the Inovation and Optimalization of Technologies for Natural Gas Dehydration(No.FR-TI1/173)
文摘This paper compares three methods for natural gas dehydration that are widely applied in industry：（1） absorption by triethylene glycol, （2） adsorption on solid desiccants and （3） condensation. A comparison is made according to their energy demand and suitability for use. The energy calculations are performed on a model where 105 Nm3/h water saturated natural gas is processed at 30 °C. The pressure of the gas varies from 7 to 20 MPa. The required outlet concentration of water in natural gas is equivalent to the dew point temperature of -10 °C at gas pressure of 4 MPa.
基金supported by the National Nature Science Foundation of China (No: 20976013)International Science & Technology Cooperation Program of China (No: 2012DFR40240)
文摘Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction,N2 adsorption-desorption measurement and NH3 temperature-programmed desorption.The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated.Among these catalysts,H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80%methanol conversion and 100%dimethyl ether selectivity in a wide temperature range of 170—300℃,and H-ZSM-5/MCM-41 prepared with nNa/nSi=0.47 showed constant methanol conversion of about 88.7%,100% dimethyl ether selectivity and excellent lifetime at 220℃.The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves.The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.
基金supported by the Petrochemical Research & Technology Company of National Petrochemical Company in Iran
文摘A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide （CTAB） as templates （samples C and D, respectively）. Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.
文摘In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.
基金supported by the Natural Science Foundation of China (No.21106143)100-talent project of Dalian Institute of Chemical Physics (DICP)the Independent Innovation Foundation of State Key Laboratory of Catalysis (No.R201113)
文摘Phosphoric acid treated niobic acid(NbP)was used for the dehydration of xylose to furfural in biphasic solvent system,which was found to exhibit the best performance among the tested catalysts.The excellent performance of NbP could be explained by the better synergistic cooperation between Bro¨nsted and Lewis acid sites.Moreover,NbP showed good stability and no obvious deactivation or leaching of Nb could be observed after six continuous recycles.
基金supported by Iranian Nanotechnology Initiative Council
文摘The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions （T = 300 ？C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h？1） and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.
文摘H-ZSM-5 zeolite was synthesized by hydrothermal method. The effects of different synthesis parameters, such as hydrothermal crystallization temperature （170-190 ℃） and Si/A1 molar ratio （100-150）, on the catalytic performance of the dehydration of methanol to dimethyl ether （DME） over the synthesized H-ZSM-5 zeolite were studied. The catalysts were characterized by N2 adsorption-desorption, XRD, NH3-TPD, TGA/DTA, and SEM techniques. The full factorial design of experiments was applied to the synthesis of H-ZSM-5 zeolite and the effects of synthesis conditions and their interaction on the yield of DME as the response variable were determined. Analysis of variance showed that two variables and their interaction significantly affected the response. According to the experimental results, the optimized catalyst prepared at 170℃ with the Si/A1 molar ratio of 100 showed the best catalytic performance among the tested H-ZSM-5 zeolite.
基金supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle,LLC, for the U. S. Department of Energy (GMV). TEM studies were performed through Oak Ridge National Laboratory’s Center for Nanophase Materials Science (CNMS) which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy
文摘Phosphorylated mesoporous carbons （PMCs） were investigated as catalysts in the dehydration of fructose to hydroxymethylfurfural （HMF）. The acidic PMCs show better selectivity to HMF compared to sulfonated carbon catalyst （SC） despite lower activity. The concentration of P-O groups on the PMC was correlated with the activity/selectivity of the catalysts; the higher the P-O concentration, the higher the activity. However, the higher the P-O content, the lower the selectivity to HME Indeed, a lower concentration of the P-O groups minimized the degradation of HMF to levulinic acid and the formation of by-products, such as humines. Stability tests showed that these systems deactivate due to the formation of humines and water insoluble by-products derived from the dehydration of fructose which blocked the catalytically active sites.
基金supported by the Isfahan University of Technology(Iran)
文摘In this research, the influence of several factors such as reaction time, catalyst weight, temperature and different solvents on dehydration reaction of fructose and glucose to 5-hydroxymethylfurfural（HMF） was surveyed. Nanosphere Al-KCC-1 silica with fibrous morphology was manufactured and used as proficient and recyclable catalyst for this reaction. SEM, TEM, BET, XRD, EDX, elemental mapping, ICP and FT-IR spectroscopy methods were applied for characterization of the Al-KCC-1（molar ratio Si/Al = 5, 40） catalysts. 162℃ and 1 h are the best conditions for the fructose dehydration. Under this situation HMF yield and selectivity are 92.9% and 94.5% respectively and fructose conversion is 98.4%. Also 170℃ and 2 h are the best conditions for the glucose dehydration. In this situation HMF yield and selectivity are 39.0% and39.9% respectively and glucose conversion is 97.8%.
基金The work was supported by the Australian Research Council Discovery Projects(grant no.DP150103842,DP180104010,DE190101618)the SOAR Fellowship,and the Sydney Nano Grand Challenge from the University of Sydney。
文摘The main challenge in the dehydration of glycerol to acrolein lies in overcoming catalystdeactivation and improving the selectivity to acrolein. The relationship between theacidity in the mesoporous channels and catalytic performance of glycerol dehydration israrely reported. In this work, to investigate the influence of acidity in the mesoporouschannels of hierarchical ZSM-5 catalysts on the dehydration of glycerol to acrolein, a seriesof hierarchical ZSM-5 zeolites with comparable mesoporous volume and mesoporous sizebut different acid properties in mesopores have been successfully prepared via alkalinetreatment. The sample with the abundant mesoporosity and highest acidity display thebest performance.
基金supported by the National Natural Science Foundation of China (No.21376136,No.21176142,No.21376140,No.21176142,and No.21466001)Program for Changjiang Scholars and Innovative Research Team in University (IRT13026)
文摘Factors influencing dehydration of xylose to furfural,such as catalyst and extract agents,were investigated.Results indicated that high-temperature water may substitute for solid and liquid acid as a catalyst,and ethyl butyrate improved furfural yield for the high distribution coefficient.A furfural yield of 75 % was obtained at200 °C for 3 h in ethyl butyrate/water.The reaction kinetics of xylose dehydration to furfural was investigated and it was found that the reaction order was 0.5,and the activation energy was 68.5 k J/mol.The rate constant k showed a clear agreement with the Arrhenius law from160 to 200 °C.
文摘The catalytic conversion of methanol to dimethyl ether(DME) over a series of home-made FER-type zeolites having different acidities and commercial γ-Al_2O_3 has been studied with the aim to understand the impact of adding water in the reactant stream on the catalytic behavior on investigated materials. Cofeeding water with methanol, the alcohol conversion was slightly reduced over the investigated zeolites while the catalytic activity of γ-Al_2O_3, the traditional catalyst of MeOH-to-DME conversion, was strongly inhibited. It was also found that, for the investigated zeolites, both the amount and the initial deposition rate of the coke formed during the reaction were reduced when water was co-fed with methanol while no significant effects on both methanol conversion and DME selectivity were observed under the investigated conditions.
基金supported by the National Natural Science Foundation of China (21472189)National Basic Research Program of China (973 Program, 2012CB215304)+2 种基金the Natural Science Foundation of Guangdong Province, China (2015A030312007)Guangdong Key Laboratory of New and Renewable Energy Research and Development (Y607jl1001)Science and Technology Planning Project of Guangdong Province, China (2015A010106010)
文摘A serial of protonated and layered transition metal oxides, including layered HTaWO6, HNbMoO6 as well as HNbWO6, were synthesized by solid-state reaction and ion-exchange. The layered HTaWO6 has been systematically studied as a solid acid to realize the dehydration of fructose to 5-hydroxymethylfurfural (HMF). The transition metal oxide samples were characterized with ICP-OES, EDS, XRD, XPS, SEM, TGA, FT-IR, N-2 adsorption-desorption and NH3-TPD. The influential factors such as reaction temperature, reaction time, solvent, catalyst amount and substrate concentration were deeply investigated. The optimized fructose conversion rate of 99% with HMF yield of 67% were achieved after 30 min at 140 degrees C in dimethylsulfoxide. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.
文摘BACKGROUND: Dehydration and its associated symptoms are among the most common chief complaints of children in rural Panama. Previous studies have shown that intravascular volume correlates to the ratio of the diameters of the inferior vena cava(IVC) to the aorta(Ao). Our study aims to determine if medical students can detect pediatric dehydration using ultrasound on patients in rural Panama. METHODS: This was a prospective, observational study conducted in the Bocas del Toro region of rural Panama. Children between the ages of 1 to 15 years presenting with diarrhea, vomiting, or parasitic infection were enrolled in the study. Ultrasound measurements of the diameters of the IVC and abdominal aorta were taken to assess for dehydration. RESULTS: A total of 59 patients were enrolled in this study. Twenty-four patients were clinically diagnosed with dehydration and 35 were classified to have normal hydration status. Of the 24 patients with dehydration, half(n=12) of these patients had an IVC/Ao ratio below the American threshold of 0.8. Of the remaining asymptomatic subjects, about half(n=18) of these subjects also had an IVC/Ao ratio below the American threshold of 0.8.CONCLUSION: Our study did not support previous literature showing that the IVC/Ao ratio is lower in children with dehydration. It is possible that the American standard for evaluating clinical dehydration is not compatible with the rural pediatric populations of Panama.
文摘In this paper, microscopic characteristics of preformed gels （PGs） and secondary cross-linked gels （SCG） with the same concentration were analyzed by atomic force microscopy （AFM）. Experimental results indicate that the microstructure of secondary cross-linked gels is a thick 3-D network, in which micro-holes and irregular macro-holes are embedded. The maximum width of the irregular macro-holes is 200 nm. In the SCG two different chemical bonds were formed, which leads to the structural inhomogeneity and the asymmetry of the crosslinking density. The structural inhomogeneity of SCG results in the formation of irregular macro-holes. The excessive cross-linking density is the primary reason for dehydration of SCG and the presence of irregular macro-holes in SCG can facilitate dehydration.
基金supported by the Science and Technology Planning Program of Tianjin(Project No.12ZXCXGX21900)
文摘A study on catalytic dehydration of 4-hydroxy-3-hexanone （HH） to 4-hexen-3-one （HO） was carried out through conversion of HH over HZSM-5 zeolite catalyst in a fixed-bed reactor （FBR） operating under almospheric pressure. The test indicated a relatively high activity of the HZSM-5 zeolite capable of achieving a HH conversion of 99.2% and a HO yield of 83.5%. Catalyst deactivation could be prevented by increasing the reaction temperature by 10 ＂C for every 20 h and adding 2.0% of piperidine in the feed. A catalyst stability test （for 100 h） in FBR showed that the catalyst was active even after 100 h of time-on-stream with HH conversion remaining at 99.2% and HO yield still reaching over 83.5%. Regenera- tion experiment showed that the regenerated catalyst demonstrated a catalytic performance comparable to the fresh one.
文摘The V-P/HZSM-5 catalyst was prepared by impregnation method using HZSM-5 zeolite as the carrier.Its catalytic activity was examined on dehydration of bio-ethanol in a self-designed fluidized bed reactor to manufacture ethylene. The effects of dehydration conditions on catalytic behaviors were investigated.The results showed that the V-P/HZSM-5 catalyst demonstrated good activity for bio-ethanol dehydration.Both bio-ethanol conversion and ethylene selectivity were over 90%under the following reaction conditions:a P/V atomic ratio of 7.5,a catahst calcination temperature of 300℃,a reaction temperature of 220℃,a bio-ethanol flow rate of 0.1 mL/min.and a catalyst dosage of 3.0 g.Furthermore,the catalyst exhibited excellent catalytic stability and regeneration capability.
基金We gratefully acknowledge the financial support from the SINOPEC(G6001-20-ZS-0412).
文摘A Zn-BDC(1,4-benzene-dicarboxylic acid)compound has been studied herein during reversibly adsorbing and desorbing water from a dimethyl formamide(DMF)solvent.The compound is structurally stable and can be reused.XRD,TG,SEM,and BET results show that the morphology,textural properties and phase can gradually transform from a non-porous compound into a porous Zn-MOF by being exposed in the steam of DMF with trace water.This dried phase[Zn(BDC)]is able to reversibly remove/uptake coordinating water molecules,which can provide Zn-BDC compound with the ability to dehydrate the solvent.
