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2002 Volume 18 Issue 2
2002, 18(02): 97-99
doi: 10.3866/PKU.WHXB20020201
Abstract:
Microcrystalline magnesium containing a small amount of manganese(i.e.microcrystal Mg(Mn)) has been prepared by an arc vaporization-condensation method. XRD indicated that the microcrystalline Mg(Mn) powder has a main phase of microcrystalline Mg remaining the hexa nal crystal structure. The TEM micrographs showed that some wadding was inlaid on the surface of the microcrystalline Mg and the particle size was about 100～500 nm. It exhibits high capacity for hydrogen storage(6.2％) and high speed for hydrogen desorption at 280 ℃. This characteristic is advantageous to the application of hydrogen storage.
Microcrystalline magnesium containing a small amount of manganese(i.e.microcrystal Mg(Mn)) has been prepared by an arc vaporization-condensation method. XRD indicated that the microcrystalline Mg(Mn) powder has a main phase of microcrystalline Mg remaining the hexa nal crystal structure. The TEM micrographs showed that some wadding was inlaid on the surface of the microcrystalline Mg and the particle size was about 100～500 nm. It exhibits high capacity for hydrogen storage(6.2％) and high speed for hydrogen desorption at 280 ℃. This characteristic is advantageous to the application of hydrogen storage.
2002, 18(02): 100-105
doi: 10.3866/PKU.WHXB20020202
Abstract:
The electronic structure,metal template effect and electrophilic substitution of 5,14-Dihydro-6,8,15,17-tetramethydibenzo [b,i][1,4,8,11] tetraaza [14] annulene and its metal complexes have been studied by using semi-empiracal method of quantum chemistry program package MOAN and ab initio of Gaussian 94.All the geometry of the metal complexes have been optimized at the level of B3LYP/6-31＋G(d).The calculated results indicated that the magnitude of metal ion radii effected the metal template to synthesize the metal complexes,in accordance to the experimental yield of the products.The active site and reactivity of electrophilic substitution was described at C7、C16.Theoretical calculation leaded to the achievement of orientation reaction of the metal complexes and the synthesis of some metal complexes .The hydrogen atoms at C7、C16 of metal complex were replaced,which were proved by 1HNMR and 19FNMR.
The electronic structure,metal template effect and electrophilic substitution of 5,14-Dihydro-6,8,15,17-tetramethydibenzo [b,i][1,4,8,11] tetraaza [14] annulene and its metal complexes have been studied by using semi-empiracal method of quantum chemistry program package MOAN and ab initio of Gaussian 94.All the geometry of the metal complexes have been optimized at the level of B3LYP/6-31＋G(d).The calculated results indicated that the magnitude of metal ion radii effected the metal template to synthesize the metal complexes,in accordance to the experimental yield of the products.The active site and reactivity of electrophilic substitution was described at C7、C16.Theoretical calculation leaded to the achievement of orientation reaction of the metal complexes and the synthesis of some metal complexes .The hydrogen atoms at C7、C16 of metal complex were replaced,which were proved by 1HNMR and 19FNMR.
2002, 18(02): 106-111
doi: 10.3866/PKU.WHXB20020203
Abstract:
Poly-2-aminopyridine was synthesized using potential cycling in the solution of 0.43 mol•dm－3 2-aminopyridine and 0.01 mol•dm－3 NaOH. There are three pairs of redox peaks on the cyclic voltammogram of poly-2-aminopyridine in the solution of 1.0 mol•dm－3 ZnCl2 (pH=4.99). The experiments of rotating ring-disk electrode(RRDE)indicate that an intermediate is generated in the initiation of polymerization. The IR spectra indicate that poly-2-aminopyridine has head-to-tail structure. According to the results of atom force microscope the average particle size of poly-2-aminopyridine is about 893.4 nm, and the average distance between particles is about 255 nm. The discharge behavior of the battery consisting poly-2-aminopyridine as cathode, and zinc as anode in an electrolytic solution of 2.5 mol•dm－3 ZnCl2＋3.0 mol•dm－3 NH4Cl (pH=5.5) is very similar to that of the battery of Li-SOCl2. The discharge curve is very flat in the middle region.
Poly-2-aminopyridine was synthesized using potential cycling in the solution of 0.43 mol•dm－3 2-aminopyridine and 0.01 mol•dm－3 NaOH. There are three pairs of redox peaks on the cyclic voltammogram of poly-2-aminopyridine in the solution of 1.0 mol•dm－3 ZnCl2 (pH=4.99). The experiments of rotating ring-disk electrode(RRDE)indicate that an intermediate is generated in the initiation of polymerization. The IR spectra indicate that poly-2-aminopyridine has head-to-tail structure. According to the results of atom force microscope the average particle size of poly-2-aminopyridine is about 893.4 nm, and the average distance between particles is about 255 nm. The discharge behavior of the battery consisting poly-2-aminopyridine as cathode, and zinc as anode in an electrolytic solution of 2.5 mol•dm－3 ZnCl2＋3.0 mol•dm－3 NH4Cl (pH=5.5) is very similar to that of the battery of Li-SOCl2. The discharge curve is very flat in the middle region.
2002, 18(02): 112-116
doi: 10.3866/PKU.WHXB20020204
Abstract:
Laser induced fluorescence excitation spectrum of － 1A1 between 420～600 nm has been measured under the supersonic free-jet conditions.CCl2 was produced by dc discharge of CCl4 seeded in Ar n gas with a ratio of 1/50.81 vibronic bands belonging to the different band systems were assigned,in which 56 vibronic bands were first labeled.Comparing LIF excitation spectra of supersonic jet-cooled CCl2 with LIF excitation spectra of CCl2 at room temperature and under total pressure about 150 Pa, we preliminarily verified the electronic state band origin to be 17 255.04 cm－1.
Laser induced fluorescence excitation spectrum of － 1A1 between 420～600 nm has been measured under the supersonic free-jet conditions.CCl2 was produced by dc discharge of CCl4 seeded in Ar n gas with a ratio of 1/50.81 vibronic bands belonging to the different band systems were assigned,in which 56 vibronic bands were first labeled.Comparing LIF excitation spectra of supersonic jet-cooled CCl2 with LIF excitation spectra of CCl2 at room temperature and under total pressure about 150 Pa, we preliminarily verified the electronic state band origin to be 17 255.04 cm－1.
2002, 18(02): 117-121
doi: 10.3866/PKU.WHXB20020205
Abstract:
Excited states b1Σ＋ and ground states X3Σ－ for molecules NX(X=F,Cl,Br) have been calculated using density functional theory(DFT) Becke 3LYP.In comparison of the calculated results with f orbitals basis set 6-311＋G(3df) and that without f orbitals basis sets cc-pvDZ and 6-311＋G,it is instructive to notice that the polarization function f orbitals significantly contribute to improve in bond lengths Re and vibration frequencies ωe for NCl and NBr,but not for NF.Therefore,the f orbitals not only play some subtle aspects in bonding for lanthanides and actinides,but also for the elements lighter than lanthanum.
Excited states b1Σ＋ and ground states X3Σ－ for molecules NX(X=F,Cl,Br) have been calculated using density functional theory(DFT) Becke 3LYP.In comparison of the calculated results with f orbitals basis set 6-311＋G(3df) and that without f orbitals basis sets cc-pvDZ and 6-311＋G,it is instructive to notice that the polarization function f orbitals significantly contribute to improve in bond lengths Re and vibration frequencies ωe for NCl and NBr,but not for NF.Therefore,the f orbitals not only play some subtle aspects in bonding for lanthanides and actinides,but also for the elements lighter than lanthanum.
2002, 18(02): 122-126
doi: 10.3866/PKU.WHXB20020206
Abstract:
This work examined the shape,half-life,Zeta potential and other properties of colloidal liquid aphrons (CLA),whose aqueous phase is composed of de-ionized water and alcohol.The volume ratio of water to alcohol varies while the concentration of water-soluble surfactant does not change.It is found that the existence of alcohol in the aqueous phase will affect the surface tension between the oil and water phase,hence the particle size and distribution of CLA will change.The influence of alcohal on the Zeta potential of CLA is very weak.The main cause of the change of stability is that alcohol molecule is embedded into the SDBS layer and a mixed soapy film is formed,which changes the intensity of the soapy film .The viscosity of the aqueous phase change also,which affects the process of drainage.When the concentration of alcohol reaches 30％,the most stable CLA appears,while the worst stable one appears at 50％. In the application of pre-dispersed solvent extraction,we need a stable and small-sized CLA with a large matter transferring area,and the cost should be low.This will be benefit for the industrialization of the method.The results of this work prove that by adding alcohol into the aqueous phase ,we can get the CLA with great satisfactory for industrial use.
This work examined the shape,half-life,Zeta potential and other properties of colloidal liquid aphrons (CLA),whose aqueous phase is composed of de-ionized water and alcohol.The volume ratio of water to alcohol varies while the concentration of water-soluble surfactant does not change.It is found that the existence of alcohol in the aqueous phase will affect the surface tension between the oil and water phase,hence the particle size and distribution of CLA will change.The influence of alcohal on the Zeta potential of CLA is very weak.The main cause of the change of stability is that alcohol molecule is embedded into the SDBS layer and a mixed soapy film is formed,which changes the intensity of the soapy film .The viscosity of the aqueous phase change also,which affects the process of drainage.When the concentration of alcohol reaches 30％,the most stable CLA appears,while the worst stable one appears at 50％. In the application of pre-dispersed solvent extraction,we need a stable and small-sized CLA with a large matter transferring area,and the cost should be low.This will be benefit for the industrialization of the method.The results of this work prove that by adding alcohol into the aqueous phase ,we can get the CLA with great satisfactory for industrial use.
2002, 18(02): 127-130
doi: 10.3866/PKU.WHXB20020207
Abstract:
Using density function theory (DFT),the geometries,electron structure,vibration frequency and enthalpy variation of the chemical reaction of (XN)4R4 (X=C,Si,Ge;R=H,CH3,NH2,OH) and its precursor compound (RXNR)2 have been calculated at B3LYP/6-311G level.The results show that (RCN)4 is more stable than (CNR)4.EZP is the smallest when R=H and the largest as R=CH3,and decreases generally as R is C,N and O.
Using density function theory (DFT),the geometries,electron structure,vibration frequency and enthalpy variation of the chemical reaction of (XN)4R4 (X=C,Si,Ge;R=H,CH3,NH2,OH) and its precursor compound (RXNR)2 have been calculated at B3LYP/6-311G level.The results show that (RCN)4 is more stable than (CNR)4.EZP is the smallest when R=H and the largest as R=CH3,and decreases generally as R is C,N and O.
2002, 18(02): 131-136
doi: 10.3866/PKU.WHXB20020208
Abstract:
A theoretical calculation is made of the nonequilibrium dissociation of the diatomic molecule with the vibration-dissociation coupling behind a strong shock wave front.The distinguishing feature of this work is to take the molecular fundamental parameters as the starting point for calculation.The master equation method is applied to study the coupling between vibrational excitation and dissociation.The vibrational transition probabilities are calculated with the SSH theory.In the neighborhood of the dissociation limit,the multi-quantum transitions are taken into account and the effect of atom recombination is considered.In a O2-Ar mixture,the variation of many of the physical quantities of O2 molecule behind a primary shock front with time are calculated out,such as the vibrational energy level distribution,the vibrational relaxation time,the dissociation incubation time,the dissociation product concentration and the dissociation rate coefficient.The calculated results are found to be in a od agreement with those experimental data given by Camac and Wray,respectively.It is demonstrated in the calculation that a quasi-steady state emerges at the late stage after the shock passage during which the vibrational energy level distribution persists almost constant,Park's model underestimates the nonequilibrium dissociation rate coefficient and Hansen's model overestimates the nonequilibrium dissociation rate coefficient.
A theoretical calculation is made of the nonequilibrium dissociation of the diatomic molecule with the vibration-dissociation coupling behind a strong shock wave front.The distinguishing feature of this work is to take the molecular fundamental parameters as the starting point for calculation.The master equation method is applied to study the coupling between vibrational excitation and dissociation.The vibrational transition probabilities are calculated with the SSH theory.In the neighborhood of the dissociation limit,the multi-quantum transitions are taken into account and the effect of atom recombination is considered.In a O2-Ar mixture,the variation of many of the physical quantities of O2 molecule behind a primary shock front with time are calculated out,such as the vibrational energy level distribution,the vibrational relaxation time,the dissociation incubation time,the dissociation product concentration and the dissociation rate coefficient.The calculated results are found to be in a od agreement with those experimental data given by Camac and Wray,respectively.It is demonstrated in the calculation that a quasi-steady state emerges at the late stage after the shock passage during which the vibrational energy level distribution persists almost constant,Park's model underestimates the nonequilibrium dissociation rate coefficient and Hansen's model overestimates the nonequilibrium dissociation rate coefficient.
2002, 18(02): 137-141
doi: 10.3866/PKU.WHXB20020209
Abstract:
A new Cellular automaton model for the bicatalytic CO＋O2 surface reaction is introduced by means of building oriented two-pointed "superstructure" in lattice.Reactions can only happen in superstructures. We use reaction probability as variable to control reactions in superstructures.We use rate-per-α as variable to determine the optimum configuration for a series of α′s occupation from 1/9 to 8/9(3×3 lattice as unit) and from 1/16 to 15/16(4×4 lattice as unit).
A new Cellular automaton model for the bicatalytic CO＋O2 surface reaction is introduced by means of building oriented two-pointed "superstructure" in lattice.Reactions can only happen in superstructures. We use reaction probability as variable to control reactions in superstructures.We use rate-per-α as variable to determine the optimum configuration for a series of α′s occupation from 1/9 to 8/9(3×3 lattice as unit) and from 1/16 to 15/16(4×4 lattice as unit).
2002, 18(02): 142-146
doi: 10.3866/PKU.WHXB20020210
Abstract:
The acidity and basicity of alkali cation exchanged Y zeolites were investigated systematically using pyridine and pyrrole as the TPD and IR spectroscopic probe respectively. It was found that the overall Lewis basicity in the modified Y zeolites increased and the Lewis acidity in the modified Y zeolites decreased as the cation was exchanged from LiY to CsY in the alkali cation series. The adsorption of benzene, toluene and ethylbenzene on Y zeolites modified by alkali cations were also studied comparatively by IR spectroscopy and TPD. The following results were obtained: (1)The adsorption of pyridine on modified Y zeolites could also be used to characterize the acidity and basicity of alkali cation exchanged Y zeolites; (2) The C－H stretching frequencies of aromatic ring, of CH3 on the side-chain of toluene, and of －CH2－ on the side-chain of ethylbenzene shifted towards lower wavenumber as the cation was exchanged from LiY to CsY; (3)The adsorption strength and the amount of sorbed aromatics on modified Y zeolites were related to the basicity of alkali cation exchanged Y zeolites.
The acidity and basicity of alkali cation exchanged Y zeolites were investigated systematically using pyridine and pyrrole as the TPD and IR spectroscopic probe respectively. It was found that the overall Lewis basicity in the modified Y zeolites increased and the Lewis acidity in the modified Y zeolites decreased as the cation was exchanged from LiY to CsY in the alkali cation series. The adsorption of benzene, toluene and ethylbenzene on Y zeolites modified by alkali cations were also studied comparatively by IR spectroscopy and TPD. The following results were obtained: (1)The adsorption of pyridine on modified Y zeolites could also be used to characterize the acidity and basicity of alkali cation exchanged Y zeolites; (2) The C－H stretching frequencies of aromatic ring, of CH3 on the side-chain of toluene, and of －CH2－ on the side-chain of ethylbenzene shifted towards lower wavenumber as the cation was exchanged from LiY to CsY; (3)The adsorption strength and the amount of sorbed aromatics on modified Y zeolites were related to the basicity of alkali cation exchanged Y zeolites.
2002, 18(02): 147-151
doi: 10.3866/PKU.WHXB20020211
Abstract:
The adsorption and oxidation of n-propyl alcohol on Pt and Pt modified with saturated adsorped Sb and S (Pt/Sbad and Pt/Sad ) electrodes were studied using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM).The results demonstrated that the oxidation of n-propyl alcohol depends strongly on the oxidation states of the electrode surface.Sb adatoms on Pt surface can adsorb oxygen at relatively low potentials,and exhibit catalytic effects for n-propyl alcohol oxidation.In comparison with n-propyl alcohol oxidation at a Pt electrode,the oxidation peak potential of n-propyl alcohol on Pt surface modified with saturated Sbad was negatively shifted about 290 mV and the peak current was doubly increased.In contrary,the oxidation of S adatoms consumes oxygen species of Pt electrode surface.Consequently,the oxidation of n-propyl alcohol was inhibited on Pt surface modified with Sbad in saturation.The EQCM studies provided quantitative results of surface mass changes during n-propyl alcohol oxidation,and have thrown new light in elucidating different effects of adatoms Sbad and Sad on Pt electrode surface towards n-propyl alcohol oxidation.
The adsorption and oxidation of n-propyl alcohol on Pt and Pt modified with saturated adsorped Sb and S (Pt/Sbad and Pt/Sad ) electrodes were studied using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM).The results demonstrated that the oxidation of n-propyl alcohol depends strongly on the oxidation states of the electrode surface.Sb adatoms on Pt surface can adsorb oxygen at relatively low potentials,and exhibit catalytic effects for n-propyl alcohol oxidation.In comparison with n-propyl alcohol oxidation at a Pt electrode,the oxidation peak potential of n-propyl alcohol on Pt surface modified with saturated Sbad was negatively shifted about 290 mV and the peak current was doubly increased.In contrary,the oxidation of S adatoms consumes oxygen species of Pt electrode surface.Consequently,the oxidation of n-propyl alcohol was inhibited on Pt surface modified with Sbad in saturation.The EQCM studies provided quantitative results of surface mass changes during n-propyl alcohol oxidation,and have thrown new light in elucidating different effects of adatoms Sbad and Sad on Pt electrode surface towards n-propyl alcohol oxidation.
2002, 18(02): 152-155
doi: 10.3866/PKU.WHXB20020212
Abstract:
New aspects of molecular interaction in corrosion inhibition are firstly reported in this investigation of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) on bronze using surface enhanced Raman scattering (SERS). The adsorption on bronze of the corrosion inhibitors 2-amino-5-mercapto-1，3，4-thiadiazole has been characterized in the AMT solution with and without Cl－ using electrochemical techniques and surface enhanced Raman spectroscopy. AMT is adsorbed in a perpendicular position at a given concentration. Cl－ and AMT are strongly coadsorbed on the surface of bronze in the presence of Cl－.
New aspects of molecular interaction in corrosion inhibition are firstly reported in this investigation of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) on bronze using surface enhanced Raman scattering (SERS). The adsorption on bronze of the corrosion inhibitors 2-amino-5-mercapto-1，3，4-thiadiazole has been characterized in the AMT solution with and without Cl－ using electrochemical techniques and surface enhanced Raman spectroscopy. AMT is adsorbed in a perpendicular position at a given concentration. Cl－ and AMT are strongly coadsorbed on the surface of bronze in the presence of Cl－.
2002, 18(02): 156-160
doi: 10.3866/PKU.WHXB20020213
Abstract:
The atmospheric corrosion of A3 steel with deposited (NH4)2SO4 particles has been investigated at 298 K and relative humidity of (85±5)％.Corrosion kinetics curves show that A3 steel with deposited (NH4)2SO4 particles corroded more seriously than that without (NH4)2SO4 particles.IR,SEM/EDAX and XPS were utilized to study the development and characterization of corrosion products.The results indicate that A3 steels with (NH4)2SO4 particles corroded much faster than that without (NH4)2SO4 particles,and the corrosion of A3 steel initiated along the deposition area of (NH4)2SO4 particles,and formed basic iron sulfate.A corrosion mechanism was proposed to explain the observation.
The atmospheric corrosion of A3 steel with deposited (NH4)2SO4 particles has been investigated at 298 K and relative humidity of (85±5)％.Corrosion kinetics curves show that A3 steel with deposited (NH4)2SO4 particles corroded more seriously than that without (NH4)2SO4 particles.IR,SEM/EDAX and XPS were utilized to study the development and characterization of corrosion products.The results indicate that A3 steels with (NH4)2SO4 particles corroded much faster than that without (NH4)2SO4 particles,and the corrosion of A3 steel initiated along the deposition area of (NH4)2SO4 particles,and formed basic iron sulfate.A corrosion mechanism was proposed to explain the observation.
2002, 18(02): 161-165
doi: 10.3866/PKU.WHXB20020214
Abstract:
The dilational viscoelasticity of the interfacial film formed by interfacial active components of crude oil at n-decane/water interface was investigated.The interfacial active components was obtained by supercritical fluid extraction and fractionation(SFEF) method from Iranian heavy oil.The properties of the two samples that have different average molecular weights and the influence of temperature on these properties were studied.The results show that the sample of higher average molecular weight has higher dynamic interfacial dilational activity.From the slope of the lg|ε|～lgω curve and the result of phase angle we can infer that the primary relaxation mechanism is not of diffusion-control but perhaps of adsorption-barrier-control.Temperature profoundly influences the dilational viscoelasticity of interfacial films of the two samples.Increasing temperature decreases the amplitude of dilational modulus and viscosity of the film,and alter the frequency response of phase angle of dilational modulus.
The dilational viscoelasticity of the interfacial film formed by interfacial active components of crude oil at n-decane/water interface was investigated.The interfacial active components was obtained by supercritical fluid extraction and fractionation(SFEF) method from Iranian heavy oil.The properties of the two samples that have different average molecular weights and the influence of temperature on these properties were studied.The results show that the sample of higher average molecular weight has higher dynamic interfacial dilational activity.From the slope of the lg|ε|～lgω curve and the result of phase angle we can infer that the primary relaxation mechanism is not of diffusion-control but perhaps of adsorption-barrier-control.Temperature profoundly influences the dilational viscoelasticity of interfacial films of the two samples.Increasing temperature decreases the amplitude of dilational modulus and viscosity of the film,and alter the frequency response of phase angle of dilational modulus.
2002, 18(02): 166-169
doi: 10.3866/PKU.WHXB20020215
Abstract:
Heat capacities of N-(p-methylphenyl)-N′-(2-pyridyl)urea were determined by low temperature adiabatic calorimetry in the temperature range of 80 to 370 K. It is found that there is no heat anomaly in this temperature region. With the experimental heat capacities thermodynamic functions were calculated. To investigate the thermal stability and decomposition characteristics of N-(p-methylphenyl)-N′-(2-pyridyl)urea, DSC and TG experiments were carried out. The results indicated that N-(p-methylphenyl)-N′-(2-pyridyl)urea started to melt at 153 ℃ and the melting peak located at 173.86 ℃. The melting enthalpy is 204.45 kJ•mol－1. The decomposition peak of N-(p-methylphenyl)-N′-(2-pyridyl)urea was found at 226.11 ℃ from DSC curve. This result is similar with that from TG and DTG experiment, in which the weight loss peak was determined as 227.2 ℃.
Heat capacities of N-(p-methylphenyl)-N′-(2-pyridyl)urea were determined by low temperature adiabatic calorimetry in the temperature range of 80 to 370 K. It is found that there is no heat anomaly in this temperature region. With the experimental heat capacities thermodynamic functions were calculated. To investigate the thermal stability and decomposition characteristics of N-(p-methylphenyl)-N′-(2-pyridyl)urea, DSC and TG experiments were carried out. The results indicated that N-(p-methylphenyl)-N′-(2-pyridyl)urea started to melt at 153 ℃ and the melting peak located at 173.86 ℃. The melting enthalpy is 204.45 kJ•mol－1. The decomposition peak of N-(p-methylphenyl)-N′-(2-pyridyl)urea was found at 226.11 ℃ from DSC curve. This result is similar with that from TG and DTG experiment, in which the weight loss peak was determined as 227.2 ℃.
2002, 18(02): 170-174
doi: 10.3866/PKU.WHXB20020216
Abstract:
A series of Pd/γ-Al2O3 catalysts modified by CeO2 and La2O3 were prepared by impregnation method with different La2O3,CeO2 dope manners.Methanol decomposition was used as a probe reaction.The structure of the catalysts was characterized by means of BET,XRD,XPS and FTIR.The results showed that a La2O3 -CeO2 solid solution was facile to form by La3＋ dissolution into CeO2 lattice.The dimension of CeO2 particles decreased,while the dispersion and crystal plane of Pd and the Pd-CeO2 interaction varied with La2O3,CeO2 dope manners.High dispersion of Pd and a strong interaction between Pd and CeO2 were observed on a La2O3 and CeO2 modified Pd/Al2O3 catalyst with La2O3-CeO2 successive dope manner,which resulted in high activity for methanol decomposition.
A series of Pd/γ-Al2O3 catalysts modified by CeO2 and La2O3 were prepared by impregnation method with different La2O3,CeO2 dope manners.Methanol decomposition was used as a probe reaction.The structure of the catalysts was characterized by means of BET,XRD,XPS and FTIR.The results showed that a La2O3 -CeO2 solid solution was facile to form by La3＋ dissolution into CeO2 lattice.The dimension of CeO2 particles decreased,while the dispersion and crystal plane of Pd and the Pd-CeO2 interaction varied with La2O3,CeO2 dope manners.High dispersion of Pd and a strong interaction between Pd and CeO2 were observed on a La2O3 and CeO2 modified Pd/Al2O3 catalyst with La2O3-CeO2 successive dope manner,which resulted in high activity for methanol decomposition.
2002, 18(02): 175-179
doi: 10.3866/PKU.WHXB20020217
Abstract:
The hydrolysis reactions of Pen-K in water and in CTAB micelles have been studied by UV spectra. The results show that CTAB micelles can inhibit the hydrolysis, but the tendency of pH value change of the hydrolysis of Pen-K in the CTAB micelles is the same as that in water, which indicates that H＋ concentration has small effect on the inhibition. The investigations of IR and micro-polarity show that the stability of Pen-K is increased by the location of some Pen-K in the railings of the CTAB micelles.
The hydrolysis reactions of Pen-K in water and in CTAB micelles have been studied by UV spectra. The results show that CTAB micelles can inhibit the hydrolysis, but the tendency of pH value change of the hydrolysis of Pen-K in the CTAB micelles is the same as that in water, which indicates that H＋ concentration has small effect on the inhibition. The investigations of IR and micro-polarity show that the stability of Pen-K is increased by the location of some Pen-K in the railings of the CTAB micelles.
2002, 18(02): 180-182
doi: 10.3866/PKU.WHXB20020218
Abstract:
Carbon-coated natural graphite has been prepared by mixing graphite particles with benzene-naphthalene copolymer and thermaly treating the mixture under a nitrogen gas flow. The coated natural graphite showed about 10％higher reversible capacity and about 7％ lower irreversible capacity as an anode material for lithium ion battery with pristine graphite. The cycling behavior of graphite was also improved after being coated. The X-ray diffraction (XRD) results showed that the rhombohedral phase fraction of natural graphite increased after being coated.
Carbon-coated natural graphite has been prepared by mixing graphite particles with benzene-naphthalene copolymer and thermaly treating the mixture under a nitrogen gas flow. The coated natural graphite showed about 10％higher reversible capacity and about 7％ lower irreversible capacity as an anode material for lithium ion battery with pristine graphite. The cycling behavior of graphite was also improved after being coated. The X-ray diffraction (XRD) results showed that the rhombohedral phase fraction of natural graphite increased after being coated.
2002, 18(02): 183-187
doi: 10.3866/PKU.WHXB20020219
Abstract:
A microelectrode is combined with micro holes formed by needling through the insulating film of carbon rod. （see Fig.1). The cyclic voltammogram(see Fig.2) of this electrode determined in solution of K3Fe(CN)6/K4Fe(CN)6 are fully identical with the theoretical curves. The limiting diffusion current determined from step scanning volt-ammetry method is in od linear relation with the concentration of K4Fe(CN)6 solution(see Fig.5) and with the square of scanning rate. The cyclic voltammetric curve of Cd2＋ in solution with base electrolyte KCl is an irreversible process(see Fig.3). The current of reduce peak (at －0.98 V vs SCE), determined from step scanning voltammetric method at 800 mV•s－1 scanning rate, is in od linear relation with the concentration of Cd2＋ at 2.55×10－5 mol•dm－3 to 1.28×10－4 mol•dm－3.
A microelectrode is combined with micro holes formed by needling through the insulating film of carbon rod. （see Fig.1). The cyclic voltammogram(see Fig.2) of this electrode determined in solution of K3Fe(CN)6/K4Fe(CN)6 are fully identical with the theoretical curves. The limiting diffusion current determined from step scanning volt-ammetry method is in od linear relation with the concentration of K4Fe(CN)6 solution(see Fig.5) and with the square of scanning rate. The cyclic voltammetric curve of Cd2＋ in solution with base electrolyte KCl is an irreversible process(see Fig.3). The current of reduce peak (at －0.98 V vs SCE), determined from step scanning voltammetric method at 800 mV•s－1 scanning rate, is in od linear relation with the concentration of Cd2＋ at 2.55×10－5 mol•dm－3 to 1.28×10－4 mol•dm－3.
2002, 18(02): 188-192
doi: 10.3866/PKU.WHXB20020220
Abstract:
The reaction processes including synthesis of LiMn2O4 with LiOH•H2O and MnO2 were studied by means of DTA under atmosphere pressure, and the result obtained could be applied as an important theoretical basis for preparing LiMn2O4. Table 1～3 show the activation energies of each reaction process obtained by using Doyle-Ozawa method and Kissinger method as follows : 66.3, 72.6, 128.1 and 113.9 kJ•mol－1. Reaction orders and frequency factors were determined by making use of Kissinger method. And the kinetic equations of each reaction were deduced. X-ray diffraction patterns（XRD）, scanning electron microscope（SEM）result and size distribution measurements Fig.3～4 show that the synthesized LiMn2O4 possesses pure phase, regular appearance and normal distribution.
The reaction processes including synthesis of LiMn2O4 with LiOH•H2O and MnO2 were studied by means of DTA under atmosphere pressure, and the result obtained could be applied as an important theoretical basis for preparing LiMn2O4. Table 1～3 show the activation energies of each reaction process obtained by using Doyle-Ozawa method and Kissinger method as follows : 66.3, 72.6, 128.1 and 113.9 kJ•mol－1. Reaction orders and frequency factors were determined by making use of Kissinger method. And the kinetic equations of each reaction were deduced. X-ray diffraction patterns（XRD）, scanning electron microscope（SEM）result and size distribution measurements Fig.3～4 show that the synthesized LiMn2O4 possesses pure phase, regular appearance and normal distribution.
