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2003 Volume 19 Issue 1
2003, 19(01): 1-3
doi: 10.3866/PKU.WHXB20030101
Abstract:
A novel sulfonated poly (phthalazinone ether sulfone ketone) resin catalyst (S-PPESK) was prepared by means of sulfonation method and characterized with titration. The catalytic activity of this new resin catalyst in the isobutene oli merization was measured in detail; it exhibited od catalytic activity and excellent isobutene dimerization selectivity. The results indicated that when the sulfonation degree (S.D.) of the catalyst increased, i.e. the acid volume of the catalyst increased, the conversion for isobutene and the selectivity for trimer increased also, while the selectivity for dimer decreased, and the selectivity for tetramer was almost unchanged.
A novel sulfonated poly (phthalazinone ether sulfone ketone) resin catalyst (S-PPESK) was prepared by means of sulfonation method and characterized with titration. The catalytic activity of this new resin catalyst in the isobutene oli merization was measured in detail; it exhibited od catalytic activity and excellent isobutene dimerization selectivity. The results indicated that when the sulfonation degree (S.D.) of the catalyst increased, i.e. the acid volume of the catalyst increased, the conversion for isobutene and the selectivity for trimer increased also, while the selectivity for dimer decreased, and the selectivity for tetramer was almost unchanged.
2003, 19(01): 4-8
doi: 10.3866/PKU.WHXB20030102
Abstract:
The binary cluster anions of Ge/Sn, Ge/Pb, Sn/Pb, Co/Ge, Co/Sn and Co/Pb binary cluster ions, produced by direct laser ablation, were studied with a Tandem TOF mass spectrometer. The experiments show that E1/E2 (E1/E2 denotes Ge/Sn, Ge/Pb and Sn/Pb) binary clusters dominantly distribute in the lower mass region, in which the number of heavy atom is much larger than that of light atom. And composition and distribution of these binary clusters indicate that their structures and properties are similar to those pure group-14 elements cluster. By laser ablating the mixtures of transition metal cobalt and group-14 elements, mass spectra showed that abundance Co/E (E denotes Ge, Sn and Pb) cluster formed in higher mass range. Magic number CoGe10－, CoSn10－ and CoPb10－ may have bi-capped tetra nal antiprism structure and is icosahedral structure. The difference between E1/E2 and Co/E binary cluster anions shows that all atoms for E1/E2 binary cluster anions are on the framework of the cage, while the cobalt atom for Co/E binary cluster is inside the cage of E.
The binary cluster anions of Ge/Sn, Ge/Pb, Sn/Pb, Co/Ge, Co/Sn and Co/Pb binary cluster ions, produced by direct laser ablation, were studied with a Tandem TOF mass spectrometer. The experiments show that E1/E2 (E1/E2 denotes Ge/Sn, Ge/Pb and Sn/Pb) binary clusters dominantly distribute in the lower mass region, in which the number of heavy atom is much larger than that of light atom. And composition and distribution of these binary clusters indicate that their structures and properties are similar to those pure group-14 elements cluster. By laser ablating the mixtures of transition metal cobalt and group-14 elements, mass spectra showed that abundance Co/E (E denotes Ge, Sn and Pb) cluster formed in higher mass range. Magic number CoGe10－, CoSn10－ and CoPb10－ may have bi-capped tetra nal antiprism structure and is icosahedral structure. The difference between E1/E2 and Co/E binary cluster anions shows that all atoms for E1/E2 binary cluster anions are on the framework of the cage, while the cobalt atom for Co/E binary cluster is inside the cage of E.
2003, 19(01): 9-12
doi: 10.3866/PKU.WHXB20030103
Abstract:
A stable CdSe nanoparticle hydrosol was prepared upon addition of mercaptoacetic acid as a stabilizer. A nanocomposite was formed based on electrostatic interactions by poly (4-vinylpyridine) quaternary ammonium with CdSe nanoparticle. The formation of nanocomposite was confirmed and characterized by infrared spectrum (IR), inductively coupled plasma atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM),UV-Vis spectrophotomery (UV-Vis), photoluminescence (PL) spectrophotometry, etc.The dispersive property and luminescence intensity of CdSe nanocrystals were improved and increased by the formation of the composite.
A stable CdSe nanoparticle hydrosol was prepared upon addition of mercaptoacetic acid as a stabilizer. A nanocomposite was formed based on electrostatic interactions by poly (4-vinylpyridine) quaternary ammonium with CdSe nanoparticle. The formation of nanocomposite was confirmed and characterized by infrared spectrum (IR), inductively coupled plasma atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM),UV-Vis spectrophotomery (UV-Vis), photoluminescence (PL) spectrophotometry, etc.The dispersive property and luminescence intensity of CdSe nanocrystals were improved and increased by the formation of the composite.
2003, 19(01): 13-16
doi: 10.3866/PKU.WHXB20030104
Abstract:
By means of molecular dynamics simulation technique, the solidification process of Ni under different cooling rates has been studied. The variation of potential energy with temperature and the relationship between the energy and the structure of molecular-cluster have also been studied. With pair distribution function and pairs analysis method, the local symmetry of molecular-cluster has been analyzed. From the view of pair’s analysis, the conclusion has been discussed.
By means of molecular dynamics simulation technique, the solidification process of Ni under different cooling rates has been studied. The variation of potential energy with temperature and the relationship between the energy and the structure of molecular-cluster have also been studied. With pair distribution function and pairs analysis method, the local symmetry of molecular-cluster has been analyzed. From the view of pair’s analysis, the conclusion has been discussed.
2003, 19(01): 17-20
doi: 10.3866/PKU.WHXB20030105
Abstract:
Nanocrystalline BaTiO3 is prepared using a stearic acid gel method. The synthesis process, crystalline structure and grain sizes of nanocrystal are investigated by differential thermal analysis, thermogravimetric analysis, infrared spectra and X-ray powder diffraction. The experimental results of dielectric properties of nanocrystal indicate that the dielectric constant ε of nanocrystal is much larger than that of bulk materials. With reducing of grain size, the ε of nanocrystalline material increases first, then it falls to smaller value. With the increment of relative humidity, the ε grows up. The relationship between ε and humidity becomes linear with high enough humidity.
Nanocrystalline BaTiO3 is prepared using a stearic acid gel method. The synthesis process, crystalline structure and grain sizes of nanocrystal are investigated by differential thermal analysis, thermogravimetric analysis, infrared spectra and X-ray powder diffraction. The experimental results of dielectric properties of nanocrystal indicate that the dielectric constant ε of nanocrystal is much larger than that of bulk materials. With reducing of grain size, the ε of nanocrystalline material increases first, then it falls to smaller value. With the increment of relative humidity, the ε grows up. The relationship between ε and humidity becomes linear with high enough humidity.
2003, 19(01): 21-24
doi: 10.3866/PKU.WHXB20030106
Abstract:
Nanoparticles of CdS, TiO2 and CdS coated with TiO2 (CdS/TiO2) are prepared respectively in reversed microemulsion which is made up of Brij35/n-hexanol/cyclohexane/water. The absorption of CdS/TiO2 composite nanoparticle in the range of visible light is stronger than the sum of CdS and TiO2. Both of the particles of CdS and TiO2 show the obvious fluorescence spectrum, which of TiO2 is much stronger than that of CdS when they are in the same concentration. However, the fluorescence of TiO2 is quenched and that of CdS decreases slightly in the CdS/TiO2 composite nanoparticle.
Nanoparticles of CdS, TiO2 and CdS coated with TiO2 (CdS/TiO2) are prepared respectively in reversed microemulsion which is made up of Brij35/n-hexanol/cyclohexane/water. The absorption of CdS/TiO2 composite nanoparticle in the range of visible light is stronger than the sum of CdS and TiO2. Both of the particles of CdS and TiO2 show the obvious fluorescence spectrum, which of TiO2 is much stronger than that of CdS when they are in the same concentration. However, the fluorescence of TiO2 is quenched and that of CdS decreases slightly in the CdS/TiO2 composite nanoparticle.
2003, 19(01): 25-29
doi: 10.3866/PKU.WHXB20030107
Abstract:
A pseudo first order Langamuir-Hinswood expression is generally used to describe heterogeneous photocatalytic kinetics, but it still uncertain whether the oxidation process occurs on TiO2 surface or in solution. Adsorption behavior and photocatalytic oxidation of methyl orange and naphthalene scarlet 3R on P-25 TiO2 have been studied in order to understand the relationship of adsorption and reaction kinetics of the azo dyes. The results showed that the adsorption of both the azo dyes is obviously influenced by pH value in solution. Significant adsorption of both the azo dyes on the catalyst has been detected at pH=3,while the adsorption decreased obviously at pH≈6.The adsorption amount of naphthalene scarlet 3R is larger than that of methyl orange under cases of pH=3 and pH≈6 due to the structural difference between the two azo dyes. No adsorption was observed at pH=9 for both the azo dyes. Rates of photocatalytic degradation of the azo dyes in different media were in the order: the acidic > the basic > the neutral condition. These facts indicated that the photocatalytic reaction carried out under different mechanism in different media. It is proposed that the photocatalysis occurs on catalyst surface under acidic condition, which may follow L-H mechanism, whereas the photocatalysis occurs in solution under basic condition. A kinetic expression for the photocatalysis under basic condition was proposed, which can be finally simplified to an apparent first order reaction kinetic equation, similar to the pseudo first order L-H expression. This may be one of the reasons that the photocatalytic degradation kinetics usually can be described by the pseudo first order L-H expression.
A pseudo first order Langamuir-Hinswood expression is generally used to describe heterogeneous photocatalytic kinetics, but it still uncertain whether the oxidation process occurs on TiO2 surface or in solution. Adsorption behavior and photocatalytic oxidation of methyl orange and naphthalene scarlet 3R on P-25 TiO2 have been studied in order to understand the relationship of adsorption and reaction kinetics of the azo dyes. The results showed that the adsorption of both the azo dyes is obviously influenced by pH value in solution. Significant adsorption of both the azo dyes on the catalyst has been detected at pH=3,while the adsorption decreased obviously at pH≈6.The adsorption amount of naphthalene scarlet 3R is larger than that of methyl orange under cases of pH=3 and pH≈6 due to the structural difference between the two azo dyes. No adsorption was observed at pH=9 for both the azo dyes. Rates of photocatalytic degradation of the azo dyes in different media were in the order: the acidic > the basic > the neutral condition. These facts indicated that the photocatalytic reaction carried out under different mechanism in different media. It is proposed that the photocatalysis occurs on catalyst surface under acidic condition, which may follow L-H mechanism, whereas the photocatalysis occurs in solution under basic condition. A kinetic expression for the photocatalysis under basic condition was proposed, which can be finally simplified to an apparent first order reaction kinetic equation, similar to the pseudo first order L-H expression. This may be one of the reasons that the photocatalytic degradation kinetics usually can be described by the pseudo first order L-H expression.
2003, 19(01): 30-34
doi: 10.3866/PKU.WHXB20030108
Abstract:
A series of ZrO2-Al2O3 composites with various compositions were synthesized through heat decomposition of metal hydroxides, which were prepared by co-precipitation with NH4OH from aqueous solution of nitrates. The samples were characterized by XRD, XPS and BET measurements. It was found that with content increasing, one component tended to dissolve into the bulk phase of the other to form solid solution first. After the dissolution reached saturation, a component started to disperse onto the surface of the crystallite of the solid solution of the other component. The formation of the separate crystalline phase of one component was observed only when its content was higher than a certain percentage. The XRD peaks of the composites were significantly broadened, and the BET specific surface areas of the composites were larger than those of the pure oxides, which suggested that the crystallites became smaller. The experimental results showed the existence of mutual dispersion of both components in this system. It means that in a certain content range, the crystallite of the solid solution of each component can accept the dispersion of the other component. The phenomenon of mutual dispersion and formation of solid solution would make the crystallites smaller, and lead to higher surface area, since the process could hinder the interface diffusion and crystallite sintering.
A series of ZrO2-Al2O3 composites with various compositions were synthesized through heat decomposition of metal hydroxides, which were prepared by co-precipitation with NH4OH from aqueous solution of nitrates. The samples were characterized by XRD, XPS and BET measurements. It was found that with content increasing, one component tended to dissolve into the bulk phase of the other to form solid solution first. After the dissolution reached saturation, a component started to disperse onto the surface of the crystallite of the solid solution of the other component. The formation of the separate crystalline phase of one component was observed only when its content was higher than a certain percentage. The XRD peaks of the composites were significantly broadened, and the BET specific surface areas of the composites were larger than those of the pure oxides, which suggested that the crystallites became smaller. The experimental results showed the existence of mutual dispersion of both components in this system. It means that in a certain content range, the crystallite of the solid solution of each component can accept the dispersion of the other component. The phenomenon of mutual dispersion and formation of solid solution would make the crystallites smaller, and lead to higher surface area, since the process could hinder the interface diffusion and crystallite sintering.
2003, 19(01): 35-39
doi: 10.3866/PKU.WHXB20030109
Abstract:
We present a detailed molecular dynamics study of the melting of Au nanoclusters with up to 8628 atoms within the framework of the embedded atom method(EAM). The simulation indicates that there exists a mesoscale nanocrystal regime in metal nanoclusters. The predicted thermodynamics properties for Au nanoclusters above 456 atoms show a linear dependence on the cluster size, whereas the melting begins from the surface of the clusters with a melting point at Tmb－Tmc(N)＝aN(－1/3). In addition, the cluster size, surface energy as well as the average root-mean-square displacement (RMSD) of the clusters in the intermediate regime have been investigated.
We present a detailed molecular dynamics study of the melting of Au nanoclusters with up to 8628 atoms within the framework of the embedded atom method(EAM). The simulation indicates that there exists a mesoscale nanocrystal regime in metal nanoclusters. The predicted thermodynamics properties for Au nanoclusters above 456 atoms show a linear dependence on the cluster size, whereas the melting begins from the surface of the clusters with a melting point at Tmb－Tmc(N)＝aN(－1/3). In addition, the cluster size, surface energy as well as the average root-mean-square displacement (RMSD) of the clusters in the intermediate regime have been investigated.
2003, 19(01): 40-45
doi: 10.3866/PKU.WHXB20030110
Abstract:
The geometries and electronic structures of the (111) surfaces of some transition-metal carbides MC(M=Ti, Zr, V, Nb) have been investigated by using the first-principle methods. The results indicate that, compared to the ideal surface, the first layer (metal layer) and second layer (carbon layer) shift inwards and outwards respectively, and as a result, the space between the first and second layer is contracted. The results of the band structure calculation show that the main components of the surface state in DOS located near or crossed by EF are dxz/dyz orbitals of the surface metal atoms, and the influence of the surface relaxation on this state has been studied. In addition, discussions about the surface core-level shifts and the surface work functions are also presented.
The geometries and electronic structures of the (111) surfaces of some transition-metal carbides MC(M=Ti, Zr, V, Nb) have been investigated by using the first-principle methods. The results indicate that, compared to the ideal surface, the first layer (metal layer) and second layer (carbon layer) shift inwards and outwards respectively, and as a result, the space between the first and second layer is contracted. The results of the band structure calculation show that the main components of the surface state in DOS located near or crossed by EF are dxz/dyz orbitals of the surface metal atoms, and the influence of the surface relaxation on this state has been studied. In addition, discussions about the surface core-level shifts and the surface work functions are also presented.
2003, 19(01): 46-50
doi: 10.3866/PKU.WHXB20030111
Abstract:
Electrochemical impedance spectroscopy(EIS) and chloride sensor were employed to study the corrosion behavior of reinforcing steel in concrete. EIS results indicated that the reinforced concrete system contains two time constants, one derived from electrical double layer of reinforcing steel and the other from concrete layer. The electrical double layer was denoted by a constant phase element other than a capacitor. Ag/AgCl chloride sensor was applied in probing and monitoring the Cl－ at steel/concrete interface. A discussion was carried out on the relationship between the electrochemical behavior of rebar and the interfacial chemistry of steel/concrete.
Electrochemical impedance spectroscopy(EIS) and chloride sensor were employed to study the corrosion behavior of reinforcing steel in concrete. EIS results indicated that the reinforced concrete system contains two time constants, one derived from electrical double layer of reinforcing steel and the other from concrete layer. The electrical double layer was denoted by a constant phase element other than a capacitor. Ag/AgCl chloride sensor was applied in probing and monitoring the Cl－ at steel/concrete interface. A discussion was carried out on the relationship between the electrochemical behavior of rebar and the interfacial chemistry of steel/concrete.
2003, 19(01): 51-54
doi: 10.3866/PKU.WHXB20030112
Abstract:
The product formation of the reaction of C2H3 radical with NO2 was studied in the gas phase under 2.66×103 Pa total pressure and 298 K. C2H3 radical was generated by laser photolysis of C2H3Br/Ar mixture. In the presence of nitric dioxide (NO2), the formation of OH radicals of the electronic ground states was monitored by laser-induced fluorescence. From the results of time resolved measurements of the OH radical concentrations, bimolecular rate constants for the reactions C2H3＋NO2 and OH(X 2Π)＋NO2 were determined as k(C2H3＋NO2)=(1.8±0.05)×10－11 cm3•molec.－1•s－1 and k(OH＋NO2)=(2.1±0.15)×10－12 cm3•molec.－1•s－1.
The product formation of the reaction of C2H3 radical with NO2 was studied in the gas phase under 2.66×103 Pa total pressure and 298 K. C2H3 radical was generated by laser photolysis of C2H3Br/Ar mixture. In the presence of nitric dioxide (NO2), the formation of OH radicals of the electronic ground states was monitored by laser-induced fluorescence. From the results of time resolved measurements of the OH radical concentrations, bimolecular rate constants for the reactions C2H3＋NO2 and OH(X 2Π)＋NO2 were determined as k(C2H3＋NO2)=(1.8±0.05)×10－11 cm3•molec.－1•s－1 and k(OH＋NO2)=(2.1±0.15)×10－12 cm3•molec.－1•s－1.
2003, 19(01): 55-59
doi: 10.3866/PKU.WHXB20030113
Abstract:
The equilibrium structures, frequencies and energies of HONO2 ,HNO3＋ , HOONO conformers and HOONO＋conformers are calculated in detail by density function theory(DFT) at B3LYP theory level with 6-311G(d) basis set. The calculated results indicate that HOONO and HOONO＋ both have three stable conformers, and HOONO has three structures with imaginary frequencies. Additionally, the potential energy curves of rotation of O－O bond of HOONO and HOONO＋ are calculated and used to discuss the geometry change between different conformers. The active vibrational modes in the photoelectron spectra (PES) of HONO2 and HOONO conformers are predicted based on our calculated equilibrium structures and vibrational frequencies.
The equilibrium structures, frequencies and energies of HONO2 ,HNO3＋ , HOONO conformers and HOONO＋conformers are calculated in detail by density function theory(DFT) at B3LYP theory level with 6-311G(d) basis set. The calculated results indicate that HOONO and HOONO＋ both have three stable conformers, and HOONO has three structures with imaginary frequencies. Additionally, the potential energy curves of rotation of O－O bond of HOONO and HOONO＋ are calculated and used to discuss the geometry change between different conformers. The active vibrational modes in the photoelectron spectra (PES) of HONO2 and HOONO conformers are predicted based on our calculated equilibrium structures and vibrational frequencies.
2003, 19(01): 60-64
doi: 10.3866/PKU.WHXB20030114
Abstract:
Adsorption and oxidation of glycine on electrodes of nanometer scale thin film of ld in alkaline solutions were investigated using in situ FTIR reflection spectroscopy and electrochemical quartz crystal microbalance(EQCM). The FTIRS results demonstrate that the dissociative adsorption of glycine on Au surface can occur at potentials as low as －0.8 V(vs SCE), which leads to produce adsorbed CN－ species (cyanide, ～2100 cm－1). When electrode potential is higher than 0.2 V, the adsorbed CN－ can be oxidized to OCN－(cyanate, 2169 cm－1); and when the potential is increased further up to 0.3 V, the Au(CN)2－ species( ld di-cyanide, 2145 cm－1)appeared as further oxidative species. It has revealed that the electrodeposited nanometer scale thin film of ld on glassy carbon substrate(nm-Au/GC) exhibited AIREs (abnormal infrared effects) for CN－ adsorption, which manifested 3 nonlinear IR spectra features: the inversion of the direction of CN－ IR band, the enhancement of IR absorption of CN－(about 20 folds) and the increase in the FWHM(full width at half maximum) of CN－ IR band. According to EQCM results, the CN－ species can adsorb strongly on Au surface and therefore inhibit the adsorption of H2O and OH－ species in low potential region. The formation of Au(CN)2－ was determined to be the main reason which caused the dramatic loss of surface mass of Au film electrode in a potential scan up to 0.6 V. The current studies are of importance in understanding the interaction between amino acids and Au film electrodes.
Adsorption and oxidation of glycine on electrodes of nanometer scale thin film of ld in alkaline solutions were investigated using in situ FTIR reflection spectroscopy and electrochemical quartz crystal microbalance(EQCM). The FTIRS results demonstrate that the dissociative adsorption of glycine on Au surface can occur at potentials as low as －0.8 V(vs SCE), which leads to produce adsorbed CN－ species (cyanide, ～2100 cm－1). When electrode potential is higher than 0.2 V, the adsorbed CN－ can be oxidized to OCN－(cyanate, 2169 cm－1); and when the potential is increased further up to 0.3 V, the Au(CN)2－ species( ld di-cyanide, 2145 cm－1)appeared as further oxidative species. It has revealed that the electrodeposited nanometer scale thin film of ld on glassy carbon substrate(nm-Au/GC) exhibited AIREs (abnormal infrared effects) for CN－ adsorption, which manifested 3 nonlinear IR spectra features: the inversion of the direction of CN－ IR band, the enhancement of IR absorption of CN－(about 20 folds) and the increase in the FWHM(full width at half maximum) of CN－ IR band. According to EQCM results, the CN－ species can adsorb strongly on Au surface and therefore inhibit the adsorption of H2O and OH－ species in low potential region. The formation of Au(CN)2－ was determined to be the main reason which caused the dramatic loss of surface mass of Au film electrode in a potential scan up to 0.6 V. The current studies are of importance in understanding the interaction between amino acids and Au film electrodes.
2003, 19(01): 65-69
doi: 10.3866/PKU.WHXB20030115
Abstract:
A novel catalyst for methanol synthesis, ZnO-promoted rhodium supported on multi-wall carbon nanotubes (MWNTs), was developed. As Rh content in catalyst is 4％(w), the catalyst has higher specific surfafic area of 99.6 m2•g－1 and activation energy of 68.8 kJ•mol－1. The highest catalytic activity of CH3OH, 411.4 mg /g cat•h, can be obtained at 563 K and under 1 Mpa (Table 1). The results of TEM, TPR and TPD showed that MWNTs can enhance the dispersion degree of Rh on the catalyst surface, increase the reduction temperature of the catalyst and the adsorption capacity of hydrogen species. These results will contribute to a better understanding of the synthergistic action of reaction components and the nature of catalytic activity center in the catalyst.
A novel catalyst for methanol synthesis, ZnO-promoted rhodium supported on multi-wall carbon nanotubes (MWNTs), was developed. As Rh content in catalyst is 4％(w), the catalyst has higher specific surfafic area of 99.6 m2•g－1 and activation energy of 68.8 kJ•mol－1. The highest catalytic activity of CH3OH, 411.4 mg /g cat•h, can be obtained at 563 K and under 1 Mpa (Table 1). The results of TEM, TPR and TPD showed that MWNTs can enhance the dispersion degree of Rh on the catalyst surface, increase the reduction temperature of the catalyst and the adsorption capacity of hydrogen species. These results will contribute to a better understanding of the synthergistic action of reaction components and the nature of catalytic activity center in the catalyst.
2003, 19(01): 70-74
doi: 10.3866/PKU.WHXB20030116
Abstract:
The effect of support pre-fluorination on the physical properties and catalytic activity of MoCo/TiO2-Al2O3 was studied by XRD, N2 adsorption ,and thiophene hydrodesulfurization (HDS).Freon (CFC-12) in wet air or in NH4F solution was used as fluorinating reagents. The influences of CFC-12 content, effect of fluorination temperature and fluorinating time on the structure and hydrodesulfurization activity of the catalysts were examined systematically. The results revealed that hydrodesulfurization activity of the catalyst fluorinated by 1％ CFC-12 at 623 K was obviously improved with an increase of 20％～30 ％ as compared with that of the unfluorinated catalyst, the commercially available BY2 catalyst, and NH4F-fluorinated catalysts. Moreover, the catalyst fluorinated by the Freon gas presented excellent stability on catalytic activity and structure.
The effect of support pre-fluorination on the physical properties and catalytic activity of MoCo/TiO2-Al2O3 was studied by XRD, N2 adsorption ,and thiophene hydrodesulfurization (HDS).Freon (CFC-12) in wet air or in NH4F solution was used as fluorinating reagents. The influences of CFC-12 content, effect of fluorination temperature and fluorinating time on the structure and hydrodesulfurization activity of the catalysts were examined systematically. The results revealed that hydrodesulfurization activity of the catalyst fluorinated by 1％ CFC-12 at 623 K was obviously improved with an increase of 20％～30 ％ as compared with that of the unfluorinated catalyst, the commercially available BY2 catalyst, and NH4F-fluorinated catalysts. Moreover, the catalyst fluorinated by the Freon gas presented excellent stability on catalytic activity and structure.
2003, 19(01): 75-78
doi: 10.3866/PKU.WHXB20030117
Abstract:
The title compounds 4,4’-oxobis(propham) (Ⅰ) (C20H24N2O5, Mr=372.41) was synthesized by the addition reaction of the corresponding 4,4’-oxobisphenyl diisocyanate with isopropanol. The crystal structure was determined by X-ray diffraction method. The crystal is of triclinic system, space group P1 with a=0.85107(17), b=0.91164(18), c=1.45701(3) nm, α=80.44(3)°, β=85.25(3)°, γ= 62.88(3)°, V=0.9922(3) nm3, Z=2, Dc=1.247 g•cm－3,μ(Mo Kα)=0.90 cm－1,F(000)=396, R=0.0520 , wR=0.1434 for 4336 observed reflections with [I >2σ(I)]. X-ray analysis reveals that interatomic distances for O(2)－C(7) is 0.12142(19), O(4)－C(17) is 0.12136(18) nm, this obviously shows the formation of C=O double bonds and distances N1…O4=0.295310 nm and N2…O2=0.2941 nm show the formation of a weak hydrogen bonds.
The title compounds 4,4’-oxobis(propham) (Ⅰ) (C20H24N2O5, Mr=372.41) was synthesized by the addition reaction of the corresponding 4,4’-oxobisphenyl diisocyanate with isopropanol. The crystal structure was determined by X-ray diffraction method. The crystal is of triclinic system, space group P1 with a=0.85107(17), b=0.91164(18), c=1.45701(3) nm, α=80.44(3)°, β=85.25(3)°, γ= 62.88(3)°, V=0.9922(3) nm3, Z=2, Dc=1.247 g•cm－3,μ(Mo Kα)=0.90 cm－1,F(000)=396, R=0.0520 , wR=0.1434 for 4336 observed reflections with [I >2σ(I)]. X-ray analysis reveals that interatomic distances for O(2)－C(7) is 0.12142(19), O(4)－C(17) is 0.12136(18) nm, this obviously shows the formation of C=O double bonds and distances N1…O4=0.295310 nm and N2…O2=0.2941 nm show the formation of a weak hydrogen bonds.
2003, 19(01): 79-81
doi: 10.3866/PKU.WHXB20030118
Abstract:
Cytosolic phospholipase A2 is consided as an important fact that will induce arthritis. We have studied the three-dimensional quantitative structure activity relationship for a series of reported pyrrolidine based inhibitors by the comparative molecular field analysis. One representative compound of the series 1a was docked onto cPLA2 (PDBcode: 1CJY) by using Dock and Autodock program to determine the most likely binding conformation to cPLA2. The strategy of all-placement search was used in the CoMFA study to give a final model with the cross-validation q2 of 0.701 and the total analysis of the CoMFA coefficients map gives insights to the design of better cPLA2 inhibitors.
Cytosolic phospholipase A2 is consided as an important fact that will induce arthritis. We have studied the three-dimensional quantitative structure activity relationship for a series of reported pyrrolidine based inhibitors by the comparative molecular field analysis. One representative compound of the series 1a was docked onto cPLA2 (PDBcode: 1CJY) by using Dock and Autodock program to determine the most likely binding conformation to cPLA2. The strategy of all-placement search was used in the CoMFA study to give a final model with the cross-validation q2 of 0.701 and the total analysis of the CoMFA coefficients map gives insights to the design of better cPLA2 inhibitors.
2003, 19(01): 82-84
doi: 10.3866/PKU.WHXB20030119
Abstract:
New tantalates Ba2LnTi2Ta3O15 (Ln=Y, La) were synthesized by Ln partial substitution for Ba in the crystal structure of Ba3TiTa4O15.The crystal structure and dielectric properties were determined by X-ray powder diffraction and dielectric measurements. The results show that Ba2YTi2Ta3O15 belongs to ferroelectric phase of tetra nal tungsten bronze structure at room temperature with unit cell parameters: a=1.236 46(4) nm, c=0.388 60(2) nm. The phase transition of Ba2YTi2Ta3O15 from ferroelectric to paraelectric occurred at 180 ℃. Ba2LaTi2Ta3O15 belongs to paraelectric phase of tetra nal tungsten bronze structure at room temperature with unit cell parameters: a=1.242 64(5) nm, c=0.391 57(2) nm. At room temperature, the dielectric constant (εr) of Ba2YTi2Ta3O15 approached 107, while Ba2LaTi2Ta3O15 ceramic approached 194,combined with a low dielectric loss of 8×10－4 at 1 MHz. Ba2LaTi2Ta3O15 might be a suitable candidate of high εr microwave dielectric ceramics.
New tantalates Ba2LnTi2Ta3O15 (Ln=Y, La) were synthesized by Ln partial substitution for Ba in the crystal structure of Ba3TiTa4O15.The crystal structure and dielectric properties were determined by X-ray powder diffraction and dielectric measurements. The results show that Ba2YTi2Ta3O15 belongs to ferroelectric phase of tetra nal tungsten bronze structure at room temperature with unit cell parameters: a=1.236 46(4) nm, c=0.388 60(2) nm. The phase transition of Ba2YTi2Ta3O15 from ferroelectric to paraelectric occurred at 180 ℃. Ba2LaTi2Ta3O15 belongs to paraelectric phase of tetra nal tungsten bronze structure at room temperature with unit cell parameters: a=1.242 64(5) nm, c=0.391 57(2) nm. At room temperature, the dielectric constant (εr) of Ba2YTi2Ta3O15 approached 107, while Ba2LaTi2Ta3O15 ceramic approached 194,combined with a low dielectric loss of 8×10－4 at 1 MHz. Ba2LaTi2Ta3O15 might be a suitable candidate of high εr microwave dielectric ceramics.
2003, 19(01): 85-89
doi: 10.3866/PKU.WHXB20030120
Abstract:
Catalytic production of hydrogen by steam reforming of methanol has been studied on a series of co-precipitated CeO2 promoted Cu/ Al2O3 catalysts under atmospheric pressure in a microreactor.Cu/CeO2/Al2O3 catalysts displayed higher activity and stability than that of Cu/ Al2O3 catalysts. Maximum methanol conversion of 95.5％and H2 selectivity of 100％ were obtained at 250 ℃, n(H2O)/n(CH3OH)=1/1,WHSV=3.28 h－1,with the catalyst containing mass fraction 20％ of CeO2.After 200 h of reaction, methanol conversion was still over 90.0％ with CeO2 promoted Cu/ Al2O3 catalyst, while the activity of Cu/ Al2O3 catalyst deactivated rapidly after 100 h of reaction. XRD and TPR results indicated that CeO2 promoter not only greatly improved the surface copper dispersion, and prevented copper crystallites from reuniting or sintering, but also made copper crystallites relatively smaller and promoted copper reduction. In addition, CeO2 could enhance water gas shift reaction, which led to the decrease of CO concentration in the reformed gases. It is suggested that the high activity, selectivity and stability of Cu/CeO2/ Al2O3 catalysts are resulted from higher copper dispersion and smaller copper crystallites, and the synergetic effect between copper and ceria.
Catalytic production of hydrogen by steam reforming of methanol has been studied on a series of co-precipitated CeO2 promoted Cu/ Al2O3 catalysts under atmospheric pressure in a microreactor.Cu/CeO2/Al2O3 catalysts displayed higher activity and stability than that of Cu/ Al2O3 catalysts. Maximum methanol conversion of 95.5％and H2 selectivity of 100％ were obtained at 250 ℃, n(H2O)/n(CH3OH)=1/1,WHSV=3.28 h－1,with the catalyst containing mass fraction 20％ of CeO2.After 200 h of reaction, methanol conversion was still over 90.0％ with CeO2 promoted Cu/ Al2O3 catalyst, while the activity of Cu/ Al2O3 catalyst deactivated rapidly after 100 h of reaction. XRD and TPR results indicated that CeO2 promoter not only greatly improved the surface copper dispersion, and prevented copper crystallites from reuniting or sintering, but also made copper crystallites relatively smaller and promoted copper reduction. In addition, CeO2 could enhance water gas shift reaction, which led to the decrease of CO concentration in the reformed gases. It is suggested that the high activity, selectivity and stability of Cu/CeO2/ Al2O3 catalysts are resulted from higher copper dispersion and smaller copper crystallites, and the synergetic effect between copper and ceria.
2003, 19(01): 90-93
doi: 10.3866/PKU.WHXB20030121
Abstract:
The Stimuli-response of hydrophilic-hydrophobic semi-IPN hydrogels consisting of polyacrylic acid (PAAc)/ poly(N-dodecyl-4-vinyl pyridinium bromide) (QPVPD) with temperature was investigated in weak alkaline and acid solution .Swelling ratio (SR) of the gels increases slowly with the increasing of temperature initially, and reaches a maximum at 28 ℃,then decreases rapidly, and reaches a minimum at 32.5 ℃.This phenomenon is mainly explained by the dissociation of hydrogen bonding in PAAc network and hydrophobic interaction of QPVPD.
The Stimuli-response of hydrophilic-hydrophobic semi-IPN hydrogels consisting of polyacrylic acid (PAAc)/ poly(N-dodecyl-4-vinyl pyridinium bromide) (QPVPD) with temperature was investigated in weak alkaline and acid solution .Swelling ratio (SR) of the gels increases slowly with the increasing of temperature initially, and reaches a maximum at 28 ℃,then decreases rapidly, and reaches a minimum at 32.5 ℃.This phenomenon is mainly explained by the dissociation of hydrogen bonding in PAAc network and hydrophobic interaction of QPVPD.
