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2002 Volume 18 Issue 3
2002, 18(03): 193-196
doi: 10.3866/PKU.WHXB20020301
Abstract:
SO2 shows a significant promoting effect on the activity of Sn0.5Ti0.5O2 solid solution catalyst for NO reduction with CO at 350 ℃. The mechanism of the promotion was studied by transient techniques combined with reaction test, XRD, XPS and TPD methods. The XPS analysis proves the existence of surface sulfur species, which was formed during the COSO2 or COSO2NO reaction. It was suggested that the surface sulfur weakened the N－O bond and promoted its split hence promoted NO reduction. Therefore, surface S is one of the more importance active site for NO reduction in the SO2NOCO reaction. The mechanism of SO2 promoted NO reduction by CO was proposed.
SO2 shows a significant promoting effect on the activity of Sn0.5Ti0.5O2 solid solution catalyst for NO reduction with CO at 350 ℃. The mechanism of the promotion was studied by transient techniques combined with reaction test, XRD, XPS and TPD methods. The XPS analysis proves the existence of surface sulfur species, which was formed during the COSO2 or COSO2NO reaction. It was suggested that the surface sulfur weakened the N－O bond and promoted its split hence promoted NO reduction. Therefore, surface S is one of the more importance active site for NO reduction in the SO2NOCO reaction. The mechanism of SO2 promoted NO reduction by CO was proposed.
2002, 18(03): 197-200
doi: 10.3866/PKU.WHXB20020302
Abstract:
Manganese acetate was complexed with citric acid in solution. The resulted complex was thermally decomposed and then treated with acid to obtain nanophaseγMnO2. Physical properties of γMnO2 were characterized by XRD,TG/DTA,TEM and AFM techniques. The effect of the reaction conditions on reaction rate and final product particle size was also studied. The results showed that the particle size could be controlled by controlling the reaction conditions, so that homogeneous and superfine particle size was obtained. A γMnO2 nanosieve membrane reactor has been set up. The conversion of the dehydrogenation reaction of cyclohexane and isopropanol in the γMnO2 nanosieve membrane reactor was increased by 20％ as compared with the conventional packed bed reactor under the same conditions.
Manganese acetate was complexed with citric acid in solution. The resulted complex was thermally decomposed and then treated with acid to obtain nanophaseγMnO2. Physical properties of γMnO2 were characterized by XRD,TG/DTA,TEM and AFM techniques. The effect of the reaction conditions on reaction rate and final product particle size was also studied. The results showed that the particle size could be controlled by controlling the reaction conditions, so that homogeneous and superfine particle size was obtained. A γMnO2 nanosieve membrane reactor has been set up. The conversion of the dehydrogenation reaction of cyclohexane and isopropanol in the γMnO2 nanosieve membrane reactor was increased by 20％ as compared with the conventional packed bed reactor under the same conditions.
2002, 18(03): 201-206
doi: 10.3866/PKU.WHXB20020303
Abstract:
Mesopore formation of Y zeolite in hydrothermal dealuminated process was studied over NH4NaY with different Na2O content.A “pseudosteady state" (PSS)was observed by merely raising temperature to 650 ℃,IR characteristic absorbency maintained and few dealumination occurred in this stage,therefore BET surface area,pore volume leveled down substantially.However,they could increase by introducing steam,even could be larger than that of the original NaY in 1 h,and could decrease by further treatment.It was pronounced that protons with high electron affinity formed in temperatureraising stage interacted strongly with frame oxygen,and brought about twist,relaxation and split of zeolite frame.However,sodalite cages with a certain amount of Na＋ kept relatively stable.Then structure could be rearranged based on the stabilized sodalites under the high temperature,hydrothermal condition,but it couldn't heal over due to the existance of extraframe alumina and amorphous silica coming from framework dealumination,only sharp faujasite with damage (defects) in sodalite could be formed.This probably is the mechanism of mesopore formation.
Mesopore formation of Y zeolite in hydrothermal dealuminated process was studied over NH4NaY with different Na2O content.A “pseudosteady state" (PSS)was observed by merely raising temperature to 650 ℃,IR characteristic absorbency maintained and few dealumination occurred in this stage,therefore BET surface area,pore volume leveled down substantially.However,they could increase by introducing steam,even could be larger than that of the original NaY in 1 h,and could decrease by further treatment.It was pronounced that protons with high electron affinity formed in temperatureraising stage interacted strongly with frame oxygen,and brought about twist,relaxation and split of zeolite frame.However,sodalite cages with a certain amount of Na＋ kept relatively stable.Then structure could be rearranged based on the stabilized sodalites under the high temperature,hydrothermal condition,but it couldn't heal over due to the existance of extraframe alumina and amorphous silica coming from framework dealumination,only sharp faujasite with damage (defects) in sodalite could be formed.This probably is the mechanism of mesopore formation.
2002, 18(03): 207-212
doi: 10.3866/PKU.WHXB20020304
Abstract:
The microstructure of aqueous supercritical sodium chloride solution was investigated by molecular dynamics simulation.Under supercritical conditions,the effect of density on the microstructure of aqueous supercritical sodium chloride solution is more pronounced than the effect of temperature.Under supercritical conditions,the gNa＋Cl－(r)has a peak value at 0.261 nm,which indicates the association between Na＋ and Cl－.The higher the supercritical temperature,the stronger the association interaction.The higher the supercritical density,the weaker the association interaction.With the increase of supercritical temperature,both the hydration factor and hydration number of Na＋ and Cl－ decrease.
The microstructure of aqueous supercritical sodium chloride solution was investigated by molecular dynamics simulation.Under supercritical conditions,the effect of density on the microstructure of aqueous supercritical sodium chloride solution is more pronounced than the effect of temperature.Under supercritical conditions,the gNa＋Cl－(r)has a peak value at 0.261 nm,which indicates the association between Na＋ and Cl－.The higher the supercritical temperature,the stronger the association interaction.The higher the supercritical density,the weaker the association interaction.With the increase of supercritical temperature,both the hydration factor and hydration number of Na＋ and Cl－ decrease.
2002, 18(03): 213-217
doi: 10.3866/PKU.WHXB20020305
Abstract:
The nanoparticle rare earth (La、Nd、Sm) BaO composite thin films were deposited through vacuum evaporation.The shape and size of the nanoparticles of the rare earth affect the photoemission photospectral response threshold of the thin films.The threshold wavelength of the photospectral response of the thin film,in which the rare earth (Sm) nanoparticle shape was sphere,was 720 nm.The threshold wavelengths of the photospectral response of the thin films,in which the rare earth (La and Nd) nanoparticles shape was long,were 650 nm and 660 nm,respectively.We obtained that the equivalent barrier around rare earth nanoparticle was 1.7～2.0 eV.Because the work functions of rare earth nanoparticles and BaO composite are different,the spatial electron distribution around the rare earth nanoparticles is changed in the composite thin films.Then the energy bands around the rare earth nanoparticles become curved.
The nanoparticle rare earth (La、Nd、Sm) BaO composite thin films were deposited through vacuum evaporation.The shape and size of the nanoparticles of the rare earth affect the photoemission photospectral response threshold of the thin films.The threshold wavelength of the photospectral response of the thin film,in which the rare earth (Sm) nanoparticle shape was sphere,was 720 nm.The threshold wavelengths of the photospectral response of the thin films,in which the rare earth (La and Nd) nanoparticles shape was long,were 650 nm and 660 nm,respectively.We obtained that the equivalent barrier around rare earth nanoparticle was 1.7～2.0 eV.Because the work functions of rare earth nanoparticles and BaO composite are different,the spatial electron distribution around the rare earth nanoparticles is changed in the composite thin films.Then the energy bands around the rare earth nanoparticles become curved.
2002, 18(03): 218-222
doi: 10.3866/PKU.WHXB20020306
Abstract:
The difference between the delayed out put signal and the output signal itself is used as a control signal,timedelayed control is applied to the course of copper anodic dissolution in phosphoric acid solution.The time of delay and the weight of the feedback are adjusted in the experiment; the influence of time delay and control strength on potentiostatic current oscillation of anodic dissolution of copper is studied.The periods and amplitudes of current oscillation are strongly dependent on the delay time and control weight.Time delay has an distinct effect on the frequency of current oscillation.This feedback performs the selfcontrol and selfadjust.Oscillation period is large at small time delay,but is small at large time delay.Time delay has a profound effect on waveform of current oscillations,and the increase of the control strength results in a bifurcation of current oscillations.Low control strength will tend to stabilize periodic orbits.With the increase of the control strength,the newly created periodic oscillation states increase, and mixedmode oscillations and these orbits can be stabilized.Under appropriate control conditions,period3 oscillations are found and can be stabilized.At higher feedback strengths,chaotic states appear.Simple integer proportions are exhibited and oscillations are controlled by the periods of inherent oscillation and the periods of delay time.The control mechanism and emergence of special oscillation are analyzed and discussed.
The difference between the delayed out put signal and the output signal itself is used as a control signal,timedelayed control is applied to the course of copper anodic dissolution in phosphoric acid solution.The time of delay and the weight of the feedback are adjusted in the experiment; the influence of time delay and control strength on potentiostatic current oscillation of anodic dissolution of copper is studied.The periods and amplitudes of current oscillation are strongly dependent on the delay time and control weight.Time delay has an distinct effect on the frequency of current oscillation.This feedback performs the selfcontrol and selfadjust.Oscillation period is large at small time delay,but is small at large time delay.Time delay has a profound effect on waveform of current oscillations,and the increase of the control strength results in a bifurcation of current oscillations.Low control strength will tend to stabilize periodic orbits.With the increase of the control strength,the newly created periodic oscillation states increase, and mixedmode oscillations and these orbits can be stabilized.Under appropriate control conditions,period3 oscillations are found and can be stabilized.At higher feedback strengths,chaotic states appear.Simple integer proportions are exhibited and oscillations are controlled by the periods of inherent oscillation and the periods of delay time.The control mechanism and emergence of special oscillation are analyzed and discussed.
2002, 18(03): 223-227
doi: 10.3866/PKU.WHXB20020307
Abstract:
The solderability deterioration of the leads of electronic components often occurs during a longer storage and operation periods in which even more excess of tin layer still remained on the upper part of intermetallics η andε phases formed between the border of Cu and Sn. In this work, hot dipped and electroplated samples with thick tin coating layer more than 120 μm have been investigated by the methods of metallograph, XPS, electrochemical testing and wettability measuring. Some samples have been heat treated at 155 ℃ for 16 h to simulate storage and operation periods. The results indicated that copper rapidly dissolved and diffused deeply into liquid tin phase and also in the solid tin during heat treatment. The dissolved copper accumulated as micro crystals ofηphase suspensing in the tin phase even exposed to the surface of tin coating layer. Close connection of ηSn couples on the tin surface aroused electrochemical corrosion of tin under a moist or acidic atmosphere. The oxidized products deteriorated the solderability of lead wires.
The solderability deterioration of the leads of electronic components often occurs during a longer storage and operation periods in which even more excess of tin layer still remained on the upper part of intermetallics η andε phases formed between the border of Cu and Sn. In this work, hot dipped and electroplated samples with thick tin coating layer more than 120 μm have been investigated by the methods of metallograph, XPS, electrochemical testing and wettability measuring. Some samples have been heat treated at 155 ℃ for 16 h to simulate storage and operation periods. The results indicated that copper rapidly dissolved and diffused deeply into liquid tin phase and also in the solid tin during heat treatment. The dissolved copper accumulated as micro crystals ofηphase suspensing in the tin phase even exposed to the surface of tin coating layer. Close connection of ηSn couples on the tin surface aroused electrochemical corrosion of tin under a moist or acidic atmosphere. The oxidized products deteriorated the solderability of lead wires.
2002, 18(03): 228-231
doi: 10.3866/PKU.WHXB20020308
Abstract:
Configurations and properties of unsaturatedcarbenoid H2C=CLiF have been obtained by using DFT method at B3LYP/6311G level.The results show that H2C=CLiF has two equilibrium configurations 1 and 2(Fig.3).The transition state of isomerization of 1 to 2 has also been obtained (Fig.3).Thermodynamic and kinetic properties of isomerization of 1 to 2 have been calculated according to statistical mechanics and transition state theory.Thermodynamic properties show that 1 is more stable than 2 in the temperature range of 100～1000 K,and the kinetic properties show that the rate of transformation from 2 to 1 is very fast.So 1 is the only “stable equilibrium species” existed in unsaturatedcarbenoid H2C=CLiF.Vibrational frequencies and infrared intensities of stable equilibrium 1 at B3LYP/6311G level have been given.
Configurations and properties of unsaturatedcarbenoid H2C=CLiF have been obtained by using DFT method at B3LYP/6311G level.The results show that H2C=CLiF has two equilibrium configurations 1 and 2(Fig.3).The transition state of isomerization of 1 to 2 has also been obtained (Fig.3).Thermodynamic and kinetic properties of isomerization of 1 to 2 have been calculated according to statistical mechanics and transition state theory.Thermodynamic properties show that 1 is more stable than 2 in the temperature range of 100～1000 K,and the kinetic properties show that the rate of transformation from 2 to 1 is very fast.So 1 is the only “stable equilibrium species” existed in unsaturatedcarbenoid H2C=CLiF.Vibrational frequencies and infrared intensities of stable equilibrium 1 at B3LYP/6311G level have been given.
2002, 18(03): 232-236
doi: 10.3866/PKU.WHXB20020309
Abstract:
A quadrupole mass spectrometer was used to diagnose the ionic products from the microwave discharge through a mixture of air and water vapor. H3O＋,NO＋ and , important primary reagent ions in the chemical ionization mass spectrometry(SIFTMS) were observed at ionic beam current of up to 10 nA. The formation mechanisms for the above ions generated in the discharge were analyzed in conjunction with the ions detectied in the cases of N2, O2 and H2O microwave discharges, respectively. Thus, various ionmolecule reactions involving the primary ions , N＋, , O＋, H2O＋ and OH＋ were proposed to be responsible for the formation of H3O＋,NO＋ and , which were also demonstrated by computer simulation based on such ionmolecule reactions.
A quadrupole mass spectrometer was used to diagnose the ionic products from the microwave discharge through a mixture of air and water vapor. H3O＋,NO＋ and , important primary reagent ions in the chemical ionization mass spectrometry(SIFTMS) were observed at ionic beam current of up to 10 nA. The formation mechanisms for the above ions generated in the discharge were analyzed in conjunction with the ions detectied in the cases of N2, O2 and H2O microwave discharges, respectively. Thus, various ionmolecule reactions involving the primary ions , N＋, , O＋, H2O＋ and OH＋ were proposed to be responsible for the formation of H3O＋,NO＋ and , which were also demonstrated by computer simulation based on such ionmolecule reactions.
2002, 18(03): 237-242
doi: 10.3866/PKU.WHXB20020310
Abstract:
Ringsubstituted groups and doping not only have a great effect on the chain structure of polyanilines, but also on their aggregated state due to its electronic and steric effect. When steric hindrance increases, the crystallinity declines. Within the same molecular chain or between different molecular chains, the forming of hydrogen bond contributes to increasing crystallinity. From SEM and XRD experiments of polymer films it was found that the crystallinity of the ringsubstituted polyanilines synthesized increases in the order of polyotoluidide(POT), poly2,5dimethoxyaniline (PDMAn) and polymchloroaniline(PmClAn). In comparison to their corresponding undoping polymers, it was concluded that proton doping of polyanilines renders their crystallinity increased. POT basically showed amorphous, while PDMAn allomorphous with low crystallinity. On the other hand, PmClAn is characterized by its molecular crystalline, being monoclinic with crystallcell parameters of a=0.679 nm, b=2.304 nm, c=0.5734 nm,α=90°, β=100.9°, and γ=90°. By using MM＋ molecular mechanics methode in HyperChem program,1HNMR and Xray diffraction data were analyzed, thereby the configuration of PmClAn chain was determined and optimized, the results show that in the macromolecular chain of PmClAn the ratio of benzoid to quinoid units is 3:2.
Ringsubstituted groups and doping not only have a great effect on the chain structure of polyanilines, but also on their aggregated state due to its electronic and steric effect. When steric hindrance increases, the crystallinity declines. Within the same molecular chain or between different molecular chains, the forming of hydrogen bond contributes to increasing crystallinity. From SEM and XRD experiments of polymer films it was found that the crystallinity of the ringsubstituted polyanilines synthesized increases in the order of polyotoluidide(POT), poly2,5dimethoxyaniline (PDMAn) and polymchloroaniline(PmClAn). In comparison to their corresponding undoping polymers, it was concluded that proton doping of polyanilines renders their crystallinity increased. POT basically showed amorphous, while PDMAn allomorphous with low crystallinity. On the other hand, PmClAn is characterized by its molecular crystalline, being monoclinic with crystallcell parameters of a=0.679 nm, b=2.304 nm, c=0.5734 nm,α=90°, β=100.9°, and γ=90°. By using MM＋ molecular mechanics methode in HyperChem program,1HNMR and Xray diffraction data were analyzed, thereby the configuration of PmClAn chain was determined and optimized, the results show that in the macromolecular chain of PmClAn the ratio of benzoid to quinoid units is 3:2.
2002, 18(03): 243-247
doi: 10.3866/PKU.WHXB20020311
Abstract:
Solvated metal atom impregnation (SMAI) method was used to prepare polymer immobilized metal catalysts under mild conditions.Several SMAI CoPd catalysts with different metal contents were prepared.These catalysts were studied by Xray diffraction (XRD),Xray photoelectron spectroscopy (XPS) and magnetic measurement.Compared with catalysts prepared by common impregnation (CI) method,the particle sizes of the metal in SMAI catalysts were much smaller.The contents of zerovalent state metallic Co and Pd in SMAI catalysts were higher than those in CI catalysts.The Co atoms were enriched on the surface for SMAI catalysts,whereas the Co atom concentration on the surface was essentially the same as in the bulk for CI catalysts.The catalytic activity of SMAI catalysts was much greater than that of CI catalysts with the same composition in hydrogenation of diacetone alcohol and O2 reduction on fuel cell electrodes.
Solvated metal atom impregnation (SMAI) method was used to prepare polymer immobilized metal catalysts under mild conditions.Several SMAI CoPd catalysts with different metal contents were prepared.These catalysts were studied by Xray diffraction (XRD),Xray photoelectron spectroscopy (XPS) and magnetic measurement.Compared with catalysts prepared by common impregnation (CI) method,the particle sizes of the metal in SMAI catalysts were much smaller.The contents of zerovalent state metallic Co and Pd in SMAI catalysts were higher than those in CI catalysts.The Co atoms were enriched on the surface for SMAI catalysts,whereas the Co atom concentration on the surface was essentially the same as in the bulk for CI catalysts.The catalytic activity of SMAI catalysts was much greater than that of CI catalysts with the same composition in hydrogenation of diacetone alcohol and O2 reduction on fuel cell electrodes.
2002, 18(03): 248-252
doi: 10.3866/PKU.WHXB20020312
Abstract:
The structures and stabilities of carboxymethylchitosan and its derivatives were studied by using quantum chemical ab initio method. The calculated results indicated that the structure of carboxymethylchitosan in which the 2 site amino group of chitose(see Fig.2) was substituted by ethyloic was more stable than that in which 6 site hydroxyl group was substituted(see Fig.3). Between two isomers of carboxymethylchitosan deriva tives(i.e.(2hydroxyl3butoxyl）propylcarboxymethylchitosan, see Fig.4), isomer 1 was more stable than isomer 2. By using the optimized geometries, the vibration spectra of isomer 1 was calculated. And it was in od agreement with recent experimental results.
The structures and stabilities of carboxymethylchitosan and its derivatives were studied by using quantum chemical ab initio method. The calculated results indicated that the structure of carboxymethylchitosan in which the 2 site amino group of chitose(see Fig.2) was substituted by ethyloic was more stable than that in which 6 site hydroxyl group was substituted(see Fig.3). Between two isomers of carboxymethylchitosan deriva tives(i.e.(2hydroxyl3butoxyl）propylcarboxymethylchitosan, see Fig.4), isomer 1 was more stable than isomer 2. By using the optimized geometries, the vibration spectra of isomer 1 was calculated. And it was in od agreement with recent experimental results.
2002, 18(03): 253-259
doi: 10.3866/PKU.WHXB20020313
Abstract:
The interactions of βDribose(RI) with metal cations in groups Ia(Li＋、Na＋、K＋、Rb＋、Cs＋)、Ib(Cu＋、Ag＋、Au＋)、Ⅱa (Mg2＋、Ca2＋ 、Sr2＋ 、Ba2＋) and Ⅱb (Zn2＋ 、Cd2＋ 、Hg2＋ ) were studied at the HartreeFock and MP2 levels employing all electron(AE) and pseudopotential treatments. Relativistic effective core potentials (RECP) were used for all the ions, with the exception of Li＋. AE and RECP treatments were tested for the Na＋、K＋、Cu＋、Mg2＋、Ca2＋ and Zn2＋ complexes; od agreement between the results of AE and RECP suggests that pseudopotentials can be used with confidence also for heavy metal cations. However, in order to ensure the precision of computation,EDEF and EBSSE must be taken into account. The deformation of βDribose caused by bivalent ions are more serious than those caused by monovalent ions. Stabilization energies(ΔE) and interaction Gibbs energies(ΔG) of complexes with bivalent ions are smaller than those with monovalent ions. Therefore, the interaction between bivalent ions and βDribose is stronger than that between monovalent ions and βDribose. And in the same group the stability of complexes decreases with increasing atomic number of the metal ions(except the Au＋RI complex), because ΔE and ΔG added with increasing atomic number of the metal ions.
The interactions of βDribose(RI) with metal cations in groups Ia(Li＋、Na＋、K＋、Rb＋、Cs＋)、Ib(Cu＋、Ag＋、Au＋)、Ⅱa (Mg2＋、Ca2＋ 、Sr2＋ 、Ba2＋) and Ⅱb (Zn2＋ 、Cd2＋ 、Hg2＋ ) were studied at the HartreeFock and MP2 levels employing all electron(AE) and pseudopotential treatments. Relativistic effective core potentials (RECP) were used for all the ions, with the exception of Li＋. AE and RECP treatments were tested for the Na＋、K＋、Cu＋、Mg2＋、Ca2＋ and Zn2＋ complexes; od agreement between the results of AE and RECP suggests that pseudopotentials can be used with confidence also for heavy metal cations. However, in order to ensure the precision of computation,EDEF and EBSSE must be taken into account. The deformation of βDribose caused by bivalent ions are more serious than those caused by monovalent ions. Stabilization energies(ΔE) and interaction Gibbs energies(ΔG) of complexes with bivalent ions are smaller than those with monovalent ions. Therefore, the interaction between bivalent ions and βDribose is stronger than that between monovalent ions and βDribose. And in the same group the stability of complexes decreases with increasing atomic number of the metal ions(except the Au＋RI complex), because ΔE and ΔG added with increasing atomic number of the metal ions.
Effect of Manganese Promoter on the Performance of Co/Al2O3 Catalysts for FischerTropsch Synthesis
2002, 18(03): 260-263
doi: 10.3866/PKU.WHXB20020314
Abstract:
The Mnmodified cobalt catalysts for FischerTropsch(FT) synthesis were characterized and tested by TPR, H2TPD, FTIR, and CO hydrogenation. It was found that a suitable addition of manganese could improve the catalytic activity and selectivity and suppress the methane and C24 hydrocarbons. XRD and FTIR results showed that the presence of Mn could improve the dispersion of active phases and favor the formation of bridgedtype adsorbed CO. A small amount of Mn could increase the uptake of hydrogen, but excess of manganese might decrease the uptake of hydrogen. Such a shift of the reaction performances was related to the change of adsorbed CO species.
The Mnmodified cobalt catalysts for FischerTropsch(FT) synthesis were characterized and tested by TPR, H2TPD, FTIR, and CO hydrogenation. It was found that a suitable addition of manganese could improve the catalytic activity and selectivity and suppress the methane and C24 hydrocarbons. XRD and FTIR results showed that the presence of Mn could improve the dispersion of active phases and favor the formation of bridgedtype adsorbed CO. A small amount of Mn could increase the uptake of hydrogen, but excess of manganese might decrease the uptake of hydrogen. Such a shift of the reaction performances was related to the change of adsorbed CO species.
2002, 18(03): 264-267
doi: 10.3866/PKU.WHXB20020315
Abstract:
The reaction between periodate and thiourea has been studied in batch,semibatch reactor and CSTR (continuous stirredtank reactor).A new periodate oscillator has been found.The nonlinear reaction system displays a single peak or oli oscillations concerning the change of pH,Pt potential and iodine absorption in batch.While,oscillations of potential on Pt and Iselective electrodes are observed in CSTR and semibatch .The oscillation behavior is dependent on [KIO4]0/[SC(NH2)2]0 ratio and the initial concentration of acid.A preliminary mechanism based on the valence change of iodine may explain the kinetic phenomena in the present reaction system.
The reaction between periodate and thiourea has been studied in batch,semibatch reactor and CSTR (continuous stirredtank reactor).A new periodate oscillator has been found.The nonlinear reaction system displays a single peak or oli oscillations concerning the change of pH,Pt potential and iodine absorption in batch.While,oscillations of potential on Pt and Iselective electrodes are observed in CSTR and semibatch .The oscillation behavior is dependent on [KIO4]0/[SC(NH2)2]0 ratio and the initial concentration of acid.A preliminary mechanism based on the valence change of iodine may explain the kinetic phenomena in the present reaction system.
2002, 18(03): 268-271
doi: 10.3866/PKU.WHXB20020316
Abstract:
The electrocatalyticoxidation of ethanol at the nickel nanowire electrode was investigated by cyclic voltammetry and the forced convection hydrodynamic method. The kinetic parameters of the reaction were measured and it was found that the rate constants of the electron transfer processes on the nanowire electrode were much higher than those reported in the literatures, but the rate constant of the step following the electron transfer process was comparable to the reported values.
The electrocatalyticoxidation of ethanol at the nickel nanowire electrode was investigated by cyclic voltammetry and the forced convection hydrodynamic method. The kinetic parameters of the reaction were measured and it was found that the rate constants of the electron transfer processes on the nanowire electrode were much higher than those reported in the literatures, but the rate constant of the step following the electron transfer process was comparable to the reported values.
2002, 18(03): 272-275
doi: 10.3866/PKU.WHXB20020317
Abstract:
Novel PMMAbased electrolyte crosslinked by ethylene glycol dimethacrylate(EGD) for lithium ion battery is prepared. As the network structure, the mechanical property of the gelled electrolyte is improved. The content of methyl methacrylate(MMA) and EGD are optimized, and the temperature dependence of conductivity is investigated. The conductivity reaches 2×10－3 S•cm－1 in the polymer electrolyte containing 25％MMA, 2％ EGD and 73％ LiBF4 (mass fraction) in ethylene carbonate(EC)/dimethyl carbonate(DMC) at room temperature, and the electrochemical stability window is about 4.80 V versus lithium. The polymer lithium ion battery with gelled PMMAbased electrolyte exhibits od electrochemical property.
Novel PMMAbased electrolyte crosslinked by ethylene glycol dimethacrylate(EGD) for lithium ion battery is prepared. As the network structure, the mechanical property of the gelled electrolyte is improved. The content of methyl methacrylate(MMA) and EGD are optimized, and the temperature dependence of conductivity is investigated. The conductivity reaches 2×10－3 S•cm－1 in the polymer electrolyte containing 25％MMA, 2％ EGD and 73％ LiBF4 (mass fraction) in ethylene carbonate(EC)/dimethyl carbonate(DMC) at room temperature, and the electrochemical stability window is about 4.80 V versus lithium. The polymer lithium ion battery with gelled PMMAbased electrolyte exhibits od electrochemical property.
2002, 18(03): 276-278
doi: 10.3866/PKU.WHXB20020318
Abstract:
It has been discovered that the coke formed in CH4 coupling under plasma can be eliminated via pure H2 discharge in the system.Eliminating coke under plasma with positive or negative high voltage in DC electric field has been compared with that in AC field.The elimination of coke takes place only on the negative of the two electrodes in DC field,while on both electrodes in AC field.The coke on the reactor walls can be eliminated with either positive or negative high voltage and in either DC or AC field.Based on the experimental facts,hypotheses of the reaction mechanism are suggested.Quantity of eliminating coke depends on diametrical ratio between reactor and the electrode,input power and electrode materials.
It has been discovered that the coke formed in CH4 coupling under plasma can be eliminated via pure H2 discharge in the system.Eliminating coke under plasma with positive or negative high voltage in DC electric field has been compared with that in AC field.The elimination of coke takes place only on the negative of the two electrodes in DC field,while on both electrodes in AC field.The coke on the reactor walls can be eliminated with either positive or negative high voltage and in either DC or AC field.Based on the experimental facts,hypotheses of the reaction mechanism are suggested.Quantity of eliminating coke depends on diametrical ratio between reactor and the electrode,input power and electrode materials.
2002, 18(03): 279-283
doi: 10.3866/PKU.WHXB20020319
Abstract:
The mesoporous MCM41 molecular sieves with superhigh surface areas were hydrothermally synthesized by means of a novel surfactant. XRD, nitrogen adsorption,SEM and pyridine TGDTA were used to characterize the crystallinity,surface area and mesoporosity and acidity of the synthesized samples. The XRD results showed that MCM41 with high crystallinity. N2 adsorption indicated that BET surface area is 1300 m2•g－1. Pyridine TPD spectra of the samples showed that the acidity of MCM41 is a weak acid. The samples have high thermal stability. The optimum crystallization time is 50～100 h.
The mesoporous MCM41 molecular sieves with superhigh surface areas were hydrothermally synthesized by means of a novel surfactant. XRD, nitrogen adsorption,SEM and pyridine TGDTA were used to characterize the crystallinity,surface area and mesoporosity and acidity of the synthesized samples. The XRD results showed that MCM41 with high crystallinity. N2 adsorption indicated that BET surface area is 1300 m2•g－1. Pyridine TPD spectra of the samples showed that the acidity of MCM41 is a weak acid. The samples have high thermal stability. The optimum crystallization time is 50～100 h.
2002, 18(03): 284-288
doi: 10.3866/PKU.WHXB20020320
Abstract:
Electroless plating on nonmetallic species requires the surface to be metallized.Typically the catalytic palladium nuclei are adsorbed on the particles via stannous chloride sensitization.In this paper,a new activation method has been developed for initiating electroless copper plating on alumina powder based on palladium chemisorption on SAMs of 3Aminopropyltriethoxysilane (APTS) in the absence of SnCl2 sensitization.XPS study indicates that chemsorption of palladium on the surfaces was achieved by bonding palladium chloride to the outwards pendant amino group of the SAMs.Therefore,the palladium is not easily to be desorpted.The metallized product was characterized by XRD,FTIR and crosssection metallography.The results showed that alumina was covered by a uniform fccstructured crystalline copper layer about 2 μm thick.This concerned activation method has the advantages of decreasing the thickness of the activation layer,improving the storage life of the activated powders and enhancing adhesion between the deposited metal and the substrate without roughening conditioning.It could also be extended to other substrates with hydroxylated surfaces.
Electroless plating on nonmetallic species requires the surface to be metallized.Typically the catalytic palladium nuclei are adsorbed on the particles via stannous chloride sensitization.In this paper,a new activation method has been developed for initiating electroless copper plating on alumina powder based on palladium chemisorption on SAMs of 3Aminopropyltriethoxysilane (APTS) in the absence of SnCl2 sensitization.XPS study indicates that chemsorption of palladium on the surfaces was achieved by bonding palladium chloride to the outwards pendant amino group of the SAMs.Therefore,the palladium is not easily to be desorpted.The metallized product was characterized by XRD,FTIR and crosssection metallography.The results showed that alumina was covered by a uniform fccstructured crystalline copper layer about 2 μm thick.This concerned activation method has the advantages of decreasing the thickness of the activation layer,improving the storage life of the activated powders and enhancing adhesion between the deposited metal and the substrate without roughening conditioning.It could also be extended to other substrates with hydroxylated surfaces.
