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2002 Volume 18 Issue 1
2002, 18(01): 1-4
doi: 10.3866/PKU.WHXB20020101
Abstract:
The catalytic behavior of molybdenum doped lanthanum vanadate for propane oxidative dehydrogenation was investigated.It was found that the addition of molybdenum showed a positive promoting effect to propane oxidative dehydrogenation.56％ and 43％ of C3H6 selectivities were obtained over LaMo0.1V0.9O4.05 at 10％ and 20％ C3H8 conversion respectively ,while the selectivities on LaVO4 were only 36％ and 22％ at the isoconversion,which can be attributed to an increase of the mobile oxygen species beneficial to propene formation and to the change of the redox properties of the molybdenum doped catalysts.
The catalytic behavior of molybdenum doped lanthanum vanadate for propane oxidative dehydrogenation was investigated.It was found that the addition of molybdenum showed a positive promoting effect to propane oxidative dehydrogenation.56％ and 43％ of C3H6 selectivities were obtained over LaMo0.1V0.9O4.05 at 10％ and 20％ C3H8 conversion respectively ,while the selectivities on LaVO4 were only 36％ and 22％ at the isoconversion,which can be attributed to an increase of the mobile oxygen species beneficial to propene formation and to the change of the redox properties of the molybdenum doped catalysts.
2002, 18(01): 5-9
doi: 10.3866/PKU.WHXB20020102
Abstract:
A variety of synthesis parameters for the preparation of Zirconia nanoparticles in watercylcohexanehexanolTriton X100 microemulsion have been investigated. The results show that reaction temperatures and the molar ratio of water to surfactant(r0) were the predominant factors to control the specific surface area as well as particle sizes of ZrO2 . The particle size first decreased with a decrease in the value of r0, then increased after reaching a critical particle size upon further decreasing the r0 value; on the other hand, an increase in the reaction temperature led to smaller ZrO2 particles, but the ZrO2 particle size became larger at a temperature close to the cloud point of the reverse micelles, where a small temperature disturbance would easily lead the system out of the microemulsion phase. XRD, TEM and N2 adsorption experiments were used to characterize the ZrO2 sample. XRD results showed that the fresh sample was amorphous, and tetra nal phase appeared as a predominant phase with a little monoclinic modification upon calcining the sample at 450 ℃, further heating the sample at 900 ℃ would lead to more monoclinic modification in intensity, but tetra nal phase was still predominant. TEM showed that the average particle size was increased from about 4 nm at 450 ℃ to about 21 nm at 900 ℃, which was in agreement with the measurements from N2 adsorption results and XRD results. N2 adsorption experiments indicated that a specific surface area of 212 m2•g－1 was obtained after optimizing the synthesis parameters and calcining the obtained sample at 450 ℃ in oxygen.
A variety of synthesis parameters for the preparation of Zirconia nanoparticles in watercylcohexanehexanolTriton X100 microemulsion have been investigated. The results show that reaction temperatures and the molar ratio of water to surfactant(r0) were the predominant factors to control the specific surface area as well as particle sizes of ZrO2 . The particle size first decreased with a decrease in the value of r0, then increased after reaching a critical particle size upon further decreasing the r0 value; on the other hand, an increase in the reaction temperature led to smaller ZrO2 particles, but the ZrO2 particle size became larger at a temperature close to the cloud point of the reverse micelles, where a small temperature disturbance would easily lead the system out of the microemulsion phase. XRD, TEM and N2 adsorption experiments were used to characterize the ZrO2 sample. XRD results showed that the fresh sample was amorphous, and tetra nal phase appeared as a predominant phase with a little monoclinic modification upon calcining the sample at 450 ℃, further heating the sample at 900 ℃ would lead to more monoclinic modification in intensity, but tetra nal phase was still predominant. TEM showed that the average particle size was increased from about 4 nm at 450 ℃ to about 21 nm at 900 ℃, which was in agreement with the measurements from N2 adsorption results and XRD results. N2 adsorption experiments indicated that a specific surface area of 212 m2•g－1 was obtained after optimizing the synthesis parameters and calcining the obtained sample at 450 ℃ in oxygen.
2002, 18(01): 10-13
doi: 10.3866/PKU.WHXB20020103
Abstract:
The conductivities in Fluoroborate glasses were calculated by molecular dynamics simulation method at near and higher than glass transition temperatures.There are seven simulated systems which coverd almost all glass formation area in Li2OLiFB2O3 system.The limited conductivities and their change with temperature,activition energy of MD simulation are well in agreement with experimental data. Some early researches showed that in fast conducting solid electrolytes one of their typical characteristics is that only one kind of carrier ion migrates.It was shown that in our simulation the contribution to electrical conductivity from F ion must be taken into account.Using activation energy data,the relative conductivites among those simulated systems and experimental systems can be explained perfectly.
The conductivities in Fluoroborate glasses were calculated by molecular dynamics simulation method at near and higher than glass transition temperatures.There are seven simulated systems which coverd almost all glass formation area in Li2OLiFB2O3 system.The limited conductivities and their change with temperature,activition energy of MD simulation are well in agreement with experimental data. Some early researches showed that in fast conducting solid electrolytes one of their typical characteristics is that only one kind of carrier ion migrates.It was shown that in our simulation the contribution to electrical conductivity from F ion must be taken into account.Using activation energy data,the relative conductivites among those simulated systems and experimental systems can be explained perfectly.
2002, 18(01): 14-20
doi: 10.3866/PKU.WHXB20020104
Abstract:
Physicochemical and electrochemical performances of long service life Ti/70％IrO230％Ta2O5 (mole fraction) anodes prepared at 450 ℃ have been investigated over the whole electrolysis time in H2SO4 solution .The results showed that the whole electrolysis process of this anode could be divided into three stages consisting of ‘active',‘stable' and ‘deactive' ones.In the first two stages,the dissolution of coated oxides was dominated (with preferential loss of IrO2 component).It was found that,in these two stages,the preferential orientations of (110) and (101) planes in IrO2 rutile decreased with the electrolysis time,and that of (002) plane increased,while the preferential orientations remained to be stabilized in the ‘deactive' region.This indicated that the loss mechanism of the catalyst coatings was changed.Electrochemical impedance spectroscopy (EIS) measurements showed a slight increase in oxygen evolution reaction resistance of the oxide catalysts while a sharp rise in totally physical impedance of the whole anode in the ‘deactive' region.Xray diffraction analysis (XRD) showed that the intensity of TiO2 rutile reflections increased with the electrolysis time,with a sharp increasing in ‘deactive' region.According to the experimental results the degradation mechanism for long service life Ti based coating anodes has been proposed.
Physicochemical and electrochemical performances of long service life Ti/70％IrO230％Ta2O5 (mole fraction) anodes prepared at 450 ℃ have been investigated over the whole electrolysis time in H2SO4 solution .The results showed that the whole electrolysis process of this anode could be divided into three stages consisting of ‘active',‘stable' and ‘deactive' ones.In the first two stages,the dissolution of coated oxides was dominated (with preferential loss of IrO2 component).It was found that,in these two stages,the preferential orientations of (110) and (101) planes in IrO2 rutile decreased with the electrolysis time,and that of (002) plane increased,while the preferential orientations remained to be stabilized in the ‘deactive' region.This indicated that the loss mechanism of the catalyst coatings was changed.Electrochemical impedance spectroscopy (EIS) measurements showed a slight increase in oxygen evolution reaction resistance of the oxide catalysts while a sharp rise in totally physical impedance of the whole anode in the ‘deactive' region.Xray diffraction analysis (XRD) showed that the intensity of TiO2 rutile reflections increased with the electrolysis time,with a sharp increasing in ‘deactive' region.According to the experimental results the degradation mechanism for long service life Ti based coating anodes has been proposed.
2002, 18(01): 21-25
doi: 10.3866/PKU.WHXB20020105
Abstract:
The mechanism of the photocatalytic processes of TiO2 particulate suspension was studied in a PEC cell by using IntensityModulated Photocurrent Spectroscopy (IMPS). Collecting the frequency dependent photocurrent response from the TiO2 particulate suspension under modulated irradiation on a Pt electrode, a complex plane of IMPS response was obtained. The upper and lower semicircles represent the cathodic reduction and anodic oxidization reaction processes of photogenerated holes and electrons, respectively. The photocatalytic mechanism and the effects of applied potentials and the addition of H2O2 were discussed in terms of the amplitude of cathodic and anodic photocurrents and the characteristic frequencies of upper and lower semicircles.
The mechanism of the photocatalytic processes of TiO2 particulate suspension was studied in a PEC cell by using IntensityModulated Photocurrent Spectroscopy (IMPS). Collecting the frequency dependent photocurrent response from the TiO2 particulate suspension under modulated irradiation on a Pt electrode, a complex plane of IMPS response was obtained. The upper and lower semicircles represent the cathodic reduction and anodic oxidization reaction processes of photogenerated holes and electrons, respectively. The photocatalytic mechanism and the effects of applied potentials and the addition of H2O2 were discussed in terms of the amplitude of cathodic and anodic photocurrents and the characteristic frequencies of upper and lower semicircles.
2002, 18(01): 26-29
doi: 10.3866/PKU.WHXB20020106
Abstract:
Using the tightbinding molecular dynamics model (TBMD),Na cluster collision processes have been studied at the different initial conditions.It has been shown that clusters with different geometric structure colliding with same cluster can produce different new cluster.Cluster with solid structure is more feasible to form a stable and large cluster than that of planar structure.For the cluster collision,the collision process is reversible.
Using the tightbinding molecular dynamics model (TBMD),Na cluster collision processes have been studied at the different initial conditions.It has been shown that clusters with different geometric structure colliding with same cluster can produce different new cluster.Cluster with solid structure is more feasible to form a stable and large cluster than that of planar structure.For the cluster collision,the collision process is reversible.
2002, 18(01): 30-33
doi: 10.3866/PKU.WHXB20020107
Abstract:
The electronic structure of the interface between cyclooctatetrene(COTH) and Ru metal is studied by the ultraviolet photoelectron spectroscopy(UPS). Three peaks are observed at 5.6, 7.9 and 10.2 eV below the Fermi level, they are related to the πCC, σCC and σCH bands of the phenyl in the COTH material respectively. The peak at 3.8 eV below the Fermi level is related to the C－C band with π characteristic orbit derived from the COTH containing eight phenyls. The highest occupied state (HOS) of COTH is at 1.8 eV below the Fermi level. The work function of COTH is only 3.2 eV, 1.0 eV lower than that of clean Ru. The results of the angle resolved ultraviolet photoelectron spectroscopy (ARUPS) suggest that the molecule of COTH is approximately parallel to the substrate surface.
The electronic structure of the interface between cyclooctatetrene(COTH) and Ru metal is studied by the ultraviolet photoelectron spectroscopy(UPS). Three peaks are observed at 5.6, 7.9 and 10.2 eV below the Fermi level, they are related to the πCC, σCC and σCH bands of the phenyl in the COTH material respectively. The peak at 3.8 eV below the Fermi level is related to the C－C band with π characteristic orbit derived from the COTH containing eight phenyls. The highest occupied state (HOS) of COTH is at 1.8 eV below the Fermi level. The work function of COTH is only 3.2 eV, 1.0 eV lower than that of clean Ru. The results of the angle resolved ultraviolet photoelectron spectroscopy (ARUPS) suggest that the molecule of COTH is approximately parallel to the substrate surface.
2002, 18(01): 34-38
doi: 10.3866/PKU.WHXB20020108
Abstract:
Optical sizedependent properties of perylene nanocrystals were studied by the addition of polyvinyl alcohol (PVA) to a water suspension of perylene nanocrystals prepared by reprecipitation method.Because PVA could bind with the nanocrystals,it will inhibit the growth of the nanocrystals,so that we could obtain stable nanocrystals with different sizes.By analyzing the absorption and excitation spectra of the nanocrystals with different sizes,it was found that their absorption and excitation peaks underwent redshift while the size of the nanocrystals increased,which may be due to the change of the interactions between perylene molecules.Also with increasing crystal size,the excimer emission of perylene nanocrystals was weakened and the decay time of the excimer was prolonged.
Optical sizedependent properties of perylene nanocrystals were studied by the addition of polyvinyl alcohol (PVA) to a water suspension of perylene nanocrystals prepared by reprecipitation method.Because PVA could bind with the nanocrystals,it will inhibit the growth of the nanocrystals,so that we could obtain stable nanocrystals with different sizes.By analyzing the absorption and excitation spectra of the nanocrystals with different sizes,it was found that their absorption and excitation peaks underwent redshift while the size of the nanocrystals increased,which may be due to the change of the interactions between perylene molecules.Also with increasing crystal size,the excimer emission of perylene nanocrystals was weakened and the decay time of the excimer was prolonged.
2002, 18(01): 39-44
doi: 10.3866/PKU.WHXB20020109
Abstract:
The microstructure of liquid Al80Fe20 alloy is studied by molecular dynamics simulation, combined with experiment of Xray diffraction. It is found that there exists an obvious prepeak in the small domain（Q=17.5 nm－1）of the structure factor, which is considered as indicative of the existence of mediumrange order(MRO) in the liquid. Furthermore, the results of MD simulation agree also well with those of experiment. The chemical shortrange order(CSRO) α and BhatisThornton(BT) partial structure factors show that there exists very strong CSRO in the liquid, which suggests that the CSRO result in the formation of MRO. The maximum and the minimum at Q=17.5 nm－1 in SFe－Fe(Q) and SAl－Fe(Q) of FaberZiman(FZ) partial structure factors also indicate the existence of superstructure in the liquid. We also calculate the coordination numbers of the system and give a structural model representing MRO clusters.
The microstructure of liquid Al80Fe20 alloy is studied by molecular dynamics simulation, combined with experiment of Xray diffraction. It is found that there exists an obvious prepeak in the small domain（Q=17.5 nm－1）of the structure factor, which is considered as indicative of the existence of mediumrange order(MRO) in the liquid. Furthermore, the results of MD simulation agree also well with those of experiment. The chemical shortrange order(CSRO) α and BhatisThornton(BT) partial structure factors show that there exists very strong CSRO in the liquid, which suggests that the CSRO result in the formation of MRO. The maximum and the minimum at Q=17.5 nm－1 in SFe－Fe(Q) and SAl－Fe(Q) of FaberZiman(FZ) partial structure factors also indicate the existence of superstructure in the liquid. We also calculate the coordination numbers of the system and give a structural model representing MRO clusters.
2002, 18(01): 45-49
doi: 10.3866/PKU.WHXB20020110
Abstract:
The cyclic reaction kinetics of carbonyl oxides (H2COO, HFCOO, F2COO and Me2COO) has been studied using the density functional method(DFT) at B3LYP(full)/6311G level. The energies and structures of reactants and products were optimized in full geometries. The transition states were found by the QST2(or QST3) method and were proved by IRC calculations. The activation thermodynamic data were calculated, based on the transition states theory, and the rate constants and frequency factors were obtained from 148.15 K to 398.15 K. The dynamic calculation results show that the carbonyl oxides easily isomering to form dioxiranes at room temperature, and the electronegative substituent can enhance cyclization of the carbonyl oxides.
The cyclic reaction kinetics of carbonyl oxides (H2COO, HFCOO, F2COO and Me2COO) has been studied using the density functional method(DFT) at B3LYP(full)/6311G level. The energies and structures of reactants and products were optimized in full geometries. The transition states were found by the QST2(or QST3) method and were proved by IRC calculations. The activation thermodynamic data were calculated, based on the transition states theory, and the rate constants and frequency factors were obtained from 148.15 K to 398.15 K. The dynamic calculation results show that the carbonyl oxides easily isomering to form dioxiranes at room temperature, and the electronegative substituent can enhance cyclization of the carbonyl oxides.
2002, 18(01): 50-54
doi: 10.3866/PKU.WHXB20020111
Abstract:
The effects of penicillin potassium salt on the cmc,the aggregation numbers and the diffusion coefficients of CTAB micelles have been studied.Addition of penicillin potassium salt increases the first cmc and the second cmc,decreases the aggregation numbers of micelles and increases the diffusion coefficient when CTAB concentration is between the first cmc and the second cmc. However,when CTAB concentration is higher than the second cmc,addition of penicillin potassium salt increases the aggregation numbers but decreases the diffusion coefficient.
The effects of penicillin potassium salt on the cmc,the aggregation numbers and the diffusion coefficients of CTAB micelles have been studied.Addition of penicillin potassium salt increases the first cmc and the second cmc,decreases the aggregation numbers of micelles and increases the diffusion coefficient when CTAB concentration is between the first cmc and the second cmc. However,when CTAB concentration is higher than the second cmc,addition of penicillin potassium salt increases the aggregation numbers but decreases the diffusion coefficient.
2002, 18(01): 55-58
doi: 10.3866/PKU.WHXB20020112
Abstract:
The variation of specific surface area and chemical reactivity of nanoKH particles treated at different temperatures has been studied. The BET surface area of nanoKH decreases with the increase of heat treatment temperature, while the chemical reactivity per unit surface increases steadily. These results indicate that the state of KH surface is changed after heat treatment. Large specific surface area of nanoKH is a major factor for its high chemical reactivity, nevertheless, the surface in an activated state with high surface energy is also an important factor for its high chemical reactivity. NanoKH alone can polymerize styrene rapidly with the formation of polystyrene.
The variation of specific surface area and chemical reactivity of nanoKH particles treated at different temperatures has been studied. The BET surface area of nanoKH decreases with the increase of heat treatment temperature, while the chemical reactivity per unit surface increases steadily. These results indicate that the state of KH surface is changed after heat treatment. Large specific surface area of nanoKH is a major factor for its high chemical reactivity, nevertheless, the surface in an activated state with high surface energy is also an important factor for its high chemical reactivity. NanoKH alone can polymerize styrene rapidly with the formation of polystyrene.
2002, 18(01): 59-61
doi: 10.3866/PKU.WHXB20020113
Abstract:
Ab initio calculations of the potential energy surface for the F＋O3 reaction have been performed using the UMP2 methods. The geometry optimizations of the reactants, products, intermediates and transition states were made at the UMP2/6311＋G level. Finally, the reaction potential barriers were calculated more accurately at the UQCISD(T)/6311＋G level. The zeropoint energies are also corrected. The results show that the fluorine atom trends intensively to react with the ozone.
Ab initio calculations of the potential energy surface for the F＋O3 reaction have been performed using the UMP2 methods. The geometry optimizations of the reactants, products, intermediates and transition states were made at the UMP2/6311＋G level. Finally, the reaction potential barriers were calculated more accurately at the UQCISD(T)/6311＋G level. The zeropoint energies are also corrected. The results show that the fluorine atom trends intensively to react with the ozone.
2002, 18(01): 62-65
doi: 10.3866/PKU.WHXB20020114
Abstract:
The adsorption of propionic acid and nbutyric acid from aqueous solution by silica gel has been studied at 293,303 and 313 K respectively.It was found that the adsorption obey stoichoimetric displacement model for adsorption at liquidsolid system (SDMA). The thermodynamics and mechanism of adsorption processes were studied on the basis of linear parameter from SDMA. The adsorption is a spontaneous, exothermic process of reduced entropy. Standard free energy change for the adsorption of nbutyric acid is larger than that of propionic acid. Standard enthalpy change for the adsorption of nbutyric acid is smaller than that of propionic acid. The equation of free energy change for adsorption was derived.
The adsorption of propionic acid and nbutyric acid from aqueous solution by silica gel has been studied at 293,303 and 313 K respectively.It was found that the adsorption obey stoichoimetric displacement model for adsorption at liquidsolid system (SDMA). The thermodynamics and mechanism of adsorption processes were studied on the basis of linear parameter from SDMA. The adsorption is a spontaneous, exothermic process of reduced entropy. Standard free energy change for the adsorption of nbutyric acid is larger than that of propionic acid. Standard enthalpy change for the adsorption of nbutyric acid is smaller than that of propionic acid. The equation of free energy change for adsorption was derived.
2002, 18(01): 66-69
doi: 10.3866/PKU.WHXB20020115
Abstract:
MoSi compound composites were synthesized by in situ reaction hot pressing. Their microstructure and phase composition were analyzed by means of scanning electron microscope(SEM), electron probe microanalyzer(EPMA) and Xray diffractometer(XRD). The results indicate that the reaction products in MoSi system vary according to the order MoSi2→Mo5Si3→Mo3Si with increasing content of Mo in mixed powders. The sintered materials are nearly fully densified except the Mo3SiMo composite,exhibiting fine and homogeneous microstructures. Both MoSi2Si and MoSi2Mo5Si3 materials have an equivalent volume fraction and display an“infiltrationflow structure”. In Mo3SiMo composite, the excess Mo phase exists in “islandstructure”.
MoSi compound composites were synthesized by in situ reaction hot pressing. Their microstructure and phase composition were analyzed by means of scanning electron microscope(SEM), electron probe microanalyzer(EPMA) and Xray diffractometer(XRD). The results indicate that the reaction products in MoSi system vary according to the order MoSi2→Mo5Si3→Mo3Si with increasing content of Mo in mixed powders. The sintered materials are nearly fully densified except the Mo3SiMo composite,exhibiting fine and homogeneous microstructures. Both MoSi2Si and MoSi2Mo5Si3 materials have an equivalent volume fraction and display an“infiltrationflow structure”. In Mo3SiMo composite, the excess Mo phase exists in “islandstructure”.
2002, 18(01): 70-73
doi: 10.3866/PKU.WHXB20020116
Abstract:
A sample cell was specially designed and improved for studying crystal growth of lysozyme using vapor diffusion approach by dynamic light scattering.Various rates of vapor diffusion can be easily achieved by adjusting the concentration of the precipitator.A series of experiments using 1,3 and 4 mol•L－1 NaCl solution and silica gel particles as precipitator were performed and lead us to the conclusion that the rate of vapor diffusion was of great importance for controlling crystal growth.For higher precipitator concentrations (3,4 mol•L－1 NaCl solutions and silica gel particles),the sizes of particles in the initial stage fluctuate very considerably,while it was not the case for lower concentrations (1 mol•L－1 NaCl solution).During the nucleation stage,the time period decreased with the increasing concentration of the precipitator,but the diameters of particles remained at about 4～6 nm in despite of different rates of vapor diffusion.This shows that the rate of forming supersaturation plays an important role in crystal growth process.
A sample cell was specially designed and improved for studying crystal growth of lysozyme using vapor diffusion approach by dynamic light scattering.Various rates of vapor diffusion can be easily achieved by adjusting the concentration of the precipitator.A series of experiments using 1,3 and 4 mol•L－1 NaCl solution and silica gel particles as precipitator were performed and lead us to the conclusion that the rate of vapor diffusion was of great importance for controlling crystal growth.For higher precipitator concentrations (3,4 mol•L－1 NaCl solutions and silica gel particles),the sizes of particles in the initial stage fluctuate very considerably,while it was not the case for lower concentrations (1 mol•L－1 NaCl solution).During the nucleation stage,the time period decreased with the increasing concentration of the precipitator,but the diameters of particles remained at about 4～6 nm in despite of different rates of vapor diffusion.This shows that the rate of forming supersaturation plays an important role in crystal growth process.
2002, 18(01): 74-78
doi: 10.3866/PKU.WHXB20020117
Abstract:
The efficiency of benzotriazole(BTA) and 8hydroxyquinoline(HQ) as corrosion inhibitors for copper was investigated in 3％ NaCl solution. Potentiodynamic polarization and a.c impedance spectroscopy were applied to study the corrosion behavior in presence of inhibitors and their complex. A synergistic effect of BTA and HQ combined inhibitors on copper corrosion was observed. The molecular structure parameters of BTA and HQ were obtained via MM2 forcefield program and PPPSCF quantum chemical calculation. The synergistic effect was attributed to the formation of a more compact protective layer.
The efficiency of benzotriazole(BTA) and 8hydroxyquinoline(HQ) as corrosion inhibitors for copper was investigated in 3％ NaCl solution. Potentiodynamic polarization and a.c impedance spectroscopy were applied to study the corrosion behavior in presence of inhibitors and their complex. A synergistic effect of BTA and HQ combined inhibitors on copper corrosion was observed. The molecular structure parameters of BTA and HQ were obtained via MM2 forcefield program and PPPSCF quantum chemical calculation. The synergistic effect was attributed to the formation of a more compact protective layer.
2002, 18(01): 79-81
doi: 10.3866/PKU.WHXB20020118
Abstract:
Watersoluble NaCl nanoparticles were prepared by reacting NaAc with HCl in ethanol/Brij 30/hexadecane microemulsion.The particles obtained are crystalline spheres with an average particle size of about 60 nm.In the case of using formamide/AOT/nheptane microemulsion as the reaction medium,NaCl particles can only be obtained by adding precipitant after the reaction.The latter particles are crystalline cubes with a much larger particle size(1 μm).The results show that nonaqueous reverse microemulsion may provide a new medium for the preparation of watersoluble nanoparticles and the choice of the polar solvent is critical to obtain nanosized materials.
Watersoluble NaCl nanoparticles were prepared by reacting NaAc with HCl in ethanol/Brij 30/hexadecane microemulsion.The particles obtained are crystalline spheres with an average particle size of about 60 nm.In the case of using formamide/AOT/nheptane microemulsion as the reaction medium,NaCl particles can only be obtained by adding precipitant after the reaction.The latter particles are crystalline cubes with a much larger particle size(1 μm).The results show that nonaqueous reverse microemulsion may provide a new medium for the preparation of watersoluble nanoparticles and the choice of the polar solvent is critical to obtain nanosized materials.
2002, 18(01): 82-86
doi: 10.3866/PKU.WHXB20020119
Abstract:
Insitu XPS and TPDMS techniques were used to study the reaction mechanism and the active center of CuNi/Zn catalyst for methanol decomposition.Significant amount of CH3OH、H2 and CO were detected during the methanol decomposition with TPDMS,however no evidences of CH4、CH3OCH3 and HCOOCH3 formation were obtained.TPDMS results indicated that O－H and C－H bonds instead of C－O bond were broken in methanol decomposition on Cu/Zn/Ni catalyst.It was found that H2 desorption from the surface of CuNi/Zn catalyst was the rate control step.Insitu XPS studies confirmed that the Zn species was easily reduced when temperature was higher than 200 ℃ in Cu/Zn catalyst.However,similar reduction of Zn was not observed in Cu/Zn/Ni catalyst.Furthermore,both Cu＋ and Cu0 species were observed in Cu/Zn/Ni catalyst.Our study indicated that active center(s) in Cu/Zn/Ni catalyst may be Cu0 and/or Cu＋ species,in which Cu＋ formed during the reaction.
Insitu XPS and TPDMS techniques were used to study the reaction mechanism and the active center of CuNi/Zn catalyst for methanol decomposition.Significant amount of CH3OH、H2 and CO were detected during the methanol decomposition with TPDMS,however no evidences of CH4、CH3OCH3 and HCOOCH3 formation were obtained.TPDMS results indicated that O－H and C－H bonds instead of C－O bond were broken in methanol decomposition on Cu/Zn/Ni catalyst.It was found that H2 desorption from the surface of CuNi/Zn catalyst was the rate control step.Insitu XPS studies confirmed that the Zn species was easily reduced when temperature was higher than 200 ℃ in Cu/Zn catalyst.However,similar reduction of Zn was not observed in Cu/Zn/Ni catalyst.Furthermore,both Cu＋ and Cu0 species were observed in Cu/Zn/Ni catalyst.Our study indicated that active center(s) in Cu/Zn/Ni catalyst may be Cu0 and/or Cu＋ species,in which Cu＋ formed during the reaction.
2002, 18(01): 87-90
doi: 10.3866/PKU.WHXB20020120
Abstract:
The structures of isomers and transition states of HBO2 system have been investigated using ab initio method at MP2/6311＋＋G(d,p) and QCISD(t)/6311＋＋G(3df,2p)//MP2/6311＋＋G(d,p) (singlepoint) levels of theory. The calculated results show that the chain like HOBO isomer(E1) is kinetically and thermodynamically the most stable isomer. The electronic structure of isomer E1 has been explored. Isomer E2 has C2v symmetry and HBO(O) structure is higher in energy than E1 by 381.72 kJ•mol－1. Because E2 is located in a deeper potential well, it is a stable isomer, and should be observed in experiments.
The structures of isomers and transition states of HBO2 system have been investigated using ab initio method at MP2/6311＋＋G(d,p) and QCISD(t)/6311＋＋G(3df,2p)//MP2/6311＋＋G(d,p) (singlepoint) levels of theory. The calculated results show that the chain like HOBO isomer(E1) is kinetically and thermodynamically the most stable isomer. The electronic structure of isomer E1 has been explored. Isomer E2 has C2v symmetry and HBO(O) structure is higher in energy than E1 by 381.72 kJ•mol－1. Because E2 is located in a deeper potential well, it is a stable isomer, and should be observed in experiments.
2002, 18(01): 91-94
doi: 10.3866/PKU.WHXB20020121
Abstract:
Effect of lanthanum on silver nanoparticles prepared by vacuum deposition has been investigated by transmission electron microscope (TEM) and scanning electron microscope (SEM) .Experimental results show that lanthanum decreases the size of the silver particles.The reason is that,with the effect of lanthanum,the atomic coherent energy of the substrate increases,the combined nanoparticles of lanthanum and silver are confined to fixed positions,thus coalesce is reduced.
Effect of lanthanum on silver nanoparticles prepared by vacuum deposition has been investigated by transmission electron microscope (TEM) and scanning electron microscope (SEM) .Experimental results show that lanthanum decreases the size of the silver particles.The reason is that,with the effect of lanthanum,the atomic coherent energy of the substrate increases,the combined nanoparticles of lanthanum and silver are confined to fixed positions,thus coalesce is reduced.
