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2008 Volume 24 Issue 7
2008, 24(07):
Abstract:
2008, 24(07): 1127-1131
doi: 10.1016/S1872-1508(08)60046-7
Abstract:
Monolith catalysts were prepared using TiO2 and ZrO2-TiO2 as supports with MnO2 as active component and Fe2O3 as promoter. The catalytic activities at low temperature and stability at high temperature for selective catalytic reduction of NOx with NH3 (NH3-SCR) in the presence of excessive O2were studied after the catalysts calcined at different temperatures. The catalystswere characterized by X-ray diffraction (XRD), specific surface area measurements (BET), oxygen storage capacity (OSC), and temperature programmed reduction (H2-TPR). The results indicated that the catalyst supported on ZrO2-TiO2 had excellent stability at high temperature, and possessed high specific surface area and oxygen storage capacity, and had strong redox property. The results of the catalytic activities indicated that the monolith manganese-based catalyst using ZrO2-TiO2 as support had evidently improved the activity of NH3-SCR reaction at low temperature, and it showed great potential for practical application.
2008, 24(07): 1132-1136
doi: 10.1016/S1872-1508(08)60047-9
Abstract:
A new volatile organic compound (VOC) combustion catalyst of 0.1%Pt-0.5%Pd/stainless steel wire mesh (SSWM) was prepared via anodic oxidation treatment. The result of activity tests for complete oxidation of toluene, acetone, and ethyl acetate showed that 0.1%Pt-0.5%Pd/steel wire mesh catalyst had od catalytic activity and thermal stability. The total oxidation temperature for toluene, acetone, and ethyl acetate was at 220, 260, and 280 ℃ for the catalyst calcined at 500 ℃, respectively. The catalyst and stainless steel wire mesh support were characterized by means of scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), and ultrasonic vibration tests. The SEMresults indicated that a typical donga structure layer appeared on the surface of stainless steel wire mesh support after anodic oxidation procedure. This typical anodic oxidation film was favorable for dispersing Pd and Pt components.
A new volatile organic compound (VOC) combustion catalyst of 0.1%Pt-0.5%Pd/stainless steel wire mesh (SSWM) was prepared via anodic oxidation treatment. The result of activity tests for complete oxidation of toluene, acetone, and ethyl acetate showed that 0.1%Pt-0.5%Pd/steel wire mesh catalyst had od catalytic activity and thermal stability. The total oxidation temperature for toluene, acetone, and ethyl acetate was at 220, 260, and 280 ℃ for the catalyst calcined at 500 ℃, respectively. The catalyst and stainless steel wire mesh support were characterized by means of scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), and ultrasonic vibration tests. The SEMresults indicated that a typical donga structure layer appeared on the surface of stainless steel wire mesh support after anodic oxidation procedure. This typical anodic oxidation film was favorable for dispersing Pd and Pt components.
2008, 24(07): 1137-1142
doi: 10.1016/S1872-1508(08)60048-0
Abstract:
A numerical study of hydrogen-enhanced liquefied petroleum gas (LPG)+air flames was presented. The variations of the adiabatic burning velocity in different conditions of combustion (φ=0.7-1.4) were studied extensively. The hydrogen content in the fuel was varied from 0% to 45% and the dilution factor was from 21% to 16%. Since the major components of LPG are butane and propane, an appropriate chemical kinetic model must be chosen to solve the chemical reaction of C3 and C4 species. Validation of the chemical kinetic model against the fundamental combustion data was performed to insure accuracy. In addition, independent simulations were conducted in the opposed-jet, symmetric, twin-flame configuration. The effects of fluid mechanics, as manifested by the induced strain rate, were also considered. The effects of extinction strain rate on flame temperature and the flammability limits were calculated and the results showed that hydrogen-enhanced LPG/air premixed flames were more stable at high flame strain. The lean flammability limits were extended by the H2 addition.
A numerical study of hydrogen-enhanced liquefied petroleum gas (LPG)+air flames was presented. The variations of the adiabatic burning velocity in different conditions of combustion (φ=0.7-1.4) were studied extensively. The hydrogen content in the fuel was varied from 0% to 45% and the dilution factor was from 21% to 16%. Since the major components of LPG are butane and propane, an appropriate chemical kinetic model must be chosen to solve the chemical reaction of C3 and C4 species. Validation of the chemical kinetic model against the fundamental combustion data was performed to insure accuracy. In addition, independent simulations were conducted in the opposed-jet, symmetric, twin-flame configuration. The effects of fluid mechanics, as manifested by the induced strain rate, were also considered. The effects of extinction strain rate on flame temperature and the flammability limits were calculated and the results showed that hydrogen-enhanced LPG/air premixed flames were more stable at high flame strain. The lean flammability limits were extended by the H2 addition.
2008, 24(07): 1143-1148
doi: 10.1016/S1872-1508(08)60049-2
Abstract:
A commercial activated carbon was modified by surface treatment using three chemicals, nitric acid, hydrogen peroxide, and ammonia, respectively. The modified carbons were characterized by N2 adsorption-desorption is otherms and FTIR spectroscopy. The resultant carbon electrode-based electric double-layer capacitors (EDLCs) were assembled with 6 mol·L-1 KOH as the electrolyte. The influence of surface modification on the performance of EDLCs was studied by galvanostatic charge-discharge, cyclic voltammetry, and alternating current impedance. The surface modification resulted in no big decrease in specific surface area and little decrease in average pore size, and introduced functional groups, such as hydroxyl, carbonyl, and amidogen, on the carbon surface. These functional groups significantly improved the wettability and reduced the resistance of the activated carbon. As a result, the specific capacitance of the carbon modified with 65%HNO3 reached 250 F·g-1, 72.4% higher than that of original carbon. The leakage current of testing EDLCs decreased unexpectedly to 3-18 μA, only 0.8%-4.9% that of the original carbon electrode-based EDLC (371 μA).
A commercial activated carbon was modified by surface treatment using three chemicals, nitric acid, hydrogen peroxide, and ammonia, respectively. The modified carbons were characterized by N2 adsorption-desorption is otherms and FTIR spectroscopy. The resultant carbon electrode-based electric double-layer capacitors (EDLCs) were assembled with 6 mol·L-1 KOH as the electrolyte. The influence of surface modification on the performance of EDLCs was studied by galvanostatic charge-discharge, cyclic voltammetry, and alternating current impedance. The surface modification resulted in no big decrease in specific surface area and little decrease in average pore size, and introduced functional groups, such as hydroxyl, carbonyl, and amidogen, on the carbon surface. These functional groups significantly improved the wettability and reduced the resistance of the activated carbon. As a result, the specific capacitance of the carbon modified with 65%HNO3 reached 250 F·g-1, 72.4% higher than that of original carbon. The leakage current of testing EDLCs decreased unexpectedly to 3-18 μA, only 0.8%-4.9% that of the original carbon electrode-based EDLC (371 μA).
2008, 24(07): 1149-1154
doi: 10.1016/S1872-1508(08)60050-9
Abstract:
The effect of cholesterol, desmosterol, stigmasterol, sitosterol, er sterol, and androsterol on the phase behavior of aqueous dispersions of dipalmitoylphosphatidylcholine (DPPC) was studied to understand the role of the side chain in the formation of ordered phases of the type observed in membrane rafts. Thermotropic changes in the structure of mixed dispersions and transition enthalpies were examined by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The observations indicated that cholesterol was more efficient than phytosterols (stigmasterol and sitosterol) or er sterol in its interaction with DPPC to form the liquid ordered phase (Lo). The Lo induced by cholesterol or desmosterol was stable over a wide temperature range, whereas, the liquid ordered phase containing phytosterols or er sterol was profoundly dependent on temperature, which should be distinguished as Loβ and Loα, representing the phases below and above the main transition temperature. The characteristics in forming ordered structures of cholesterol and other sterols imply that the evolution may have selected cholesterol as the most efficient sterol for animals to formrafts in their cell membranes.
The effect of cholesterol, desmosterol, stigmasterol, sitosterol, er sterol, and androsterol on the phase behavior of aqueous dispersions of dipalmitoylphosphatidylcholine (DPPC) was studied to understand the role of the side chain in the formation of ordered phases of the type observed in membrane rafts. Thermotropic changes in the structure of mixed dispersions and transition enthalpies were examined by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The observations indicated that cholesterol was more efficient than phytosterols (stigmasterol and sitosterol) or er sterol in its interaction with DPPC to form the liquid ordered phase (Lo). The Lo induced by cholesterol or desmosterol was stable over a wide temperature range, whereas, the liquid ordered phase containing phytosterols or er sterol was profoundly dependent on temperature, which should be distinguished as Loβ and Loα, representing the phases below and above the main transition temperature. The characteristics in forming ordered structures of cholesterol and other sterols imply that the evolution may have selected cholesterol as the most efficient sterol for animals to formrafts in their cell membranes.
2008, 24(07): 1155-1159
doi: 10.1016/S1872-1508(08)60051-0
Abstract:
A new energetic compound (TAGH)2(TNR) (TAG: triaminoguanidine, TNR: 2,4,6-trinitroresorcinol) was prepared by reacting triaminoguanidine with 2,4,6-trinitroresorcinol (styphnic acid) in aqueous solution under nitrogen atmosphere, and characterized by elemental analysis and Fourier transform infrared (FTIR) spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belonged to a monoclinic, C2/c space group. The unit cell parameters were as follows: a=2.2892(6) nm, b=1.2802(3) nm, c=1.3661(4) nm, β=111.174(5)°, V=3.7333(16) nm3, and Z=8. The compound consisted of two cations C(N2H3)+3 and an anion (C6HN3O8)2-. The C(N2H3)+3 and (C6HN3O8)2- were bonded together by electrostatic attraction and hydrogen bonds, and this effect made the compound more stable. The thermal analysis of the compound was studied by using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TG-DTG). Under nitrogen atmosphere with a heating rate of 10 K·min-1, the thermal decomposition of the compound contained only one intense exothermic decomposition process in the range of 450.1-477.7 K in the DSC curve, and the decomposition products were nearly gaseous products.
A new energetic compound (TAGH)2(TNR) (TAG: triaminoguanidine, TNR: 2,4,6-trinitroresorcinol) was prepared by reacting triaminoguanidine with 2,4,6-trinitroresorcinol (styphnic acid) in aqueous solution under nitrogen atmosphere, and characterized by elemental analysis and Fourier transform infrared (FTIR) spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belonged to a monoclinic, C2/c space group. The unit cell parameters were as follows: a=2.2892(6) nm, b=1.2802(3) nm, c=1.3661(4) nm, β=111.174(5)°, V=3.7333(16) nm3, and Z=8. The compound consisted of two cations C(N2H3)+3 and an anion (C6HN3O8)2-. The C(N2H3)+3 and (C6HN3O8)2- were bonded together by electrostatic attraction and hydrogen bonds, and this effect made the compound more stable. The thermal analysis of the compound was studied by using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TG-DTG). Under nitrogen atmosphere with a heating rate of 10 K·min-1, the thermal decomposition of the compound contained only one intense exothermic decomposition process in the range of 450.1-477.7 K in the DSC curve, and the decomposition products were nearly gaseous products.
2008, 24(07): 1160-1164
doi: 10.3866/PKU.WHXB20080707
Abstract:
SiC films were grown at substrate temperature of 900 ℃ by solid source molecular beam epitaxy (SSMBE) on Si(111) with different thicknesses (0, 0.2, 1 nm ) of Ge predeposited on Si prior to the epitaxy of SiC. The films were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), Fourier transforminfrared spectroscopy (FTIR). The results indicated that the quality of the film with Ge predeposition of 0.2 nm was the best. The surface of the sample was even and there were no voids observed. The Ge prdeposition of 0.2 nm suppressed the Si diffusion and decreased the void formation. For the sample without Ge predeposition, the roughness of the surface was larger and there were some voids and Si grains on the surface. For the sample with the Ge prdeposition of 1 nm, island growth mode of Ge caused the surface of SiC films rougher and the crystalline quality of SiC filmworse and even induced the formation of the polycrystalline SiC film.
SiC films were grown at substrate temperature of 900 ℃ by solid source molecular beam epitaxy (SSMBE) on Si(111) with different thicknesses (0, 0.2, 1 nm ) of Ge predeposited on Si prior to the epitaxy of SiC. The films were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), Fourier transforminfrared spectroscopy (FTIR). The results indicated that the quality of the film with Ge predeposition of 0.2 nm was the best. The surface of the sample was even and there were no voids observed. The Ge prdeposition of 0.2 nm suppressed the Si diffusion and decreased the void formation. For the sample without Ge predeposition, the roughness of the surface was larger and there were some voids and Si grains on the surface. For the sample with the Ge prdeposition of 1 nm, island growth mode of Ge caused the surface of SiC films rougher and the crystalline quality of SiC filmworse and even induced the formation of the polycrystalline SiC film.
2008, 24(07): 1165-1168
doi: 10.3866/PKU.WHXB20080708
Abstract:
Pure and Co-doped ZnO nanorods were synthesized by hydrothermal method at low temperature using Zn(NO3)2·6H2O and Co(NO3)2·6H2O as raw materials. The as-prepared samples were studied by XRD, EDS, TEM, and HRTEM, the photoluminescence (PL) property of the samples was principally investigated by PL spectroscopy. The results showed that the crystallinities of pure and ZnO:Co nanorods were rather well. Co atoms substituted Zn atoms positions to incorporate into nanocrystal, the dopant content was about 2%(atomic fraction). The average diameter and length of pure ZnO nanorods were about 20 and 180 nm, whereas the corresponding parameters of doped nanorods were respectively about 15 and 200 nm. This indicated that Co doping could influence the growth of ZnO nanorods. In addition, the Co doping could tune the energy level structure and enrich the surface states of ZnO nanorods, which led to emission peak redshift in UV region and luminescence enhancement in visible light region.
Pure and Co-doped ZnO nanorods were synthesized by hydrothermal method at low temperature using Zn(NO3)2·6H2O and Co(NO3)2·6H2O as raw materials. The as-prepared samples were studied by XRD, EDS, TEM, and HRTEM, the photoluminescence (PL) property of the samples was principally investigated by PL spectroscopy. The results showed that the crystallinities of pure and ZnO:Co nanorods were rather well. Co atoms substituted Zn atoms positions to incorporate into nanocrystal, the dopant content was about 2%(atomic fraction). The average diameter and length of pure ZnO nanorods were about 20 and 180 nm, whereas the corresponding parameters of doped nanorods were respectively about 15 and 200 nm. This indicated that Co doping could influence the growth of ZnO nanorods. In addition, the Co doping could tune the energy level structure and enrich the surface states of ZnO nanorods, which led to emission peak redshift in UV region and luminescence enhancement in visible light region.
2008, 24(07): 1169-1174
doi: 10.3866/PKU.WHXB20080709
Abstract:
In order to know more about the microcosmic structure of the important biochemical model molecule formamide (FM) in aqueous solution, the Optimized Potentials for Liquid Simulations-All Atom(OPLSAA) model were used in the molecular dynamics (MD) simulation for the aqueous solution of FMin the whole concentration range. The radial distribution functions of the solutions were obtained. The interaction between water molecule and FMmolecule was analyzed and calculated. It was found that there was a weak interaction (C—H…O) between the C—H beside the carbonyl of FM and water. The weak interaction could not be ignored, which was suggested to be significant in preventing the tautomerization of FM, especially when the concentration of FM increased in the aqueous solution of FM. By doing the calculation in the whole concentration range of the aqueous solution of FM, it was found that FM could strengthen the local structure of water in water-rich region. As the concentration increased, the association of water itself would be replaced by cross-association between water and FM gradually. In the FM-rich region, it was mainly the linear association of FMitself.
In order to know more about the microcosmic structure of the important biochemical model molecule formamide (FM) in aqueous solution, the Optimized Potentials for Liquid Simulations-All Atom(OPLSAA) model were used in the molecular dynamics (MD) simulation for the aqueous solution of FMin the whole concentration range. The radial distribution functions of the solutions were obtained. The interaction between water molecule and FMmolecule was analyzed and calculated. It was found that there was a weak interaction (C—H…O) between the C—H beside the carbonyl of FM and water. The weak interaction could not be ignored, which was suggested to be significant in preventing the tautomerization of FM, especially when the concentration of FM increased in the aqueous solution of FM. By doing the calculation in the whole concentration range of the aqueous solution of FM, it was found that FM could strengthen the local structure of water in water-rich region. As the concentration increased, the association of water itself would be replaced by cross-association between water and FM gradually. In the FM-rich region, it was mainly the linear association of FMitself.
2008, 24(07): 1175-1179
doi: 10.3866/PKU.WHXB20080710
Abstract:
LiCo1/3Ni1/3Mn1/3O2 was coated by a layer of Y2O3 via a simple method. The bared sample was immersed into Y(NO3)3·6H2O solution and then calcined at a certain temperature to get the coated material. The coated and bared LiCo1/3Ni1/3Mn1/3O2 meterials were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), cyclic voltammetry (CV), and galvanotactic charge-discharge test. It was showed that Y2O3 existed only on the surface, and had no effect on the crystal structure; the LiCo1/3Ni1/3Mn1/3O2 coated with Y2O3 exhibited better capacity retention than the bared LiCo1/3Ni1/3Mn1/3O2 in the higher cutoff voltage and had higher thermal stability. CV results suggested that the Y2O3 coating suppressed the phase transitions and prevented the surface of cathode materials fromdirect contact with the electrolyte.
LiCo1/3Ni1/3Mn1/3O2 was coated by a layer of Y2O3 via a simple method. The bared sample was immersed into Y(NO3)3·6H2O solution and then calcined at a certain temperature to get the coated material. The coated and bared LiCo1/3Ni1/3Mn1/3O2 meterials were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), cyclic voltammetry (CV), and galvanotactic charge-discharge test. It was showed that Y2O3 existed only on the surface, and had no effect on the crystal structure; the LiCo1/3Ni1/3Mn1/3O2 coated with Y2O3 exhibited better capacity retention than the bared LiCo1/3Ni1/3Mn1/3O2 in the higher cutoff voltage and had higher thermal stability. CV results suggested that the Y2O3 coating suppressed the phase transitions and prevented the surface of cathode materials fromdirect contact with the electrolyte.
2008, 24(07): 1180-1184
doi: 10.1016/S1872-1508(08)60052-2
Abstract:
The effects of nonelectrolytes (ureas, amino acids, sugars) on the cloud point (CP) of nonionic surfactant Triton X-114 (TX-114) and tetra-n-butylammonium bromide (TBAB) system were studied. Ureas as well as thioureas increased the CP. Behaviors of amino acids depended upon their nature. Nonpolar and uncharged polar amino acids were less effective in changing the CP. However, tryptophan and phenylalanine increased the CP sharply. Acidic amino acid (aspartic acid) and sugars decreased the CP. The results were explained in terms of their effect on water structure. Amino acids t solubilized either in the micellar interior or in the bulk phase.
The effects of nonelectrolytes (ureas, amino acids, sugars) on the cloud point (CP) of nonionic surfactant Triton X-114 (TX-114) and tetra-n-butylammonium bromide (TBAB) system were studied. Ureas as well as thioureas increased the CP. Behaviors of amino acids depended upon their nature. Nonpolar and uncharged polar amino acids were less effective in changing the CP. However, tryptophan and phenylalanine increased the CP sharply. Acidic amino acid (aspartic acid) and sugars decreased the CP. The results were explained in terms of their effect on water structure. Amino acids t solubilized either in the micellar interior or in the bulk phase.
2008, 24(07): 1185-1191
doi: 10.1016/S1872-1508(08)60053-4
Abstract:
The inhibition effect of 1,1’-thiocarbonyldiimidazole (TCDI) on the corrosion behaviors of mild steel (MS) in 0.5 mol·L -1 H2SO4 solution was studied with the help of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) techniques. The effect of immersion time on the inhibition effect of TCDI was also investigated over 72 h. For the long-term tests, hydrogen evolution with immersion time (VH2-t) was measured in addition to the three techniques already mentioned. The thermodynamic parameters, such as adsorption equilibrium constant (Kads) and adsorption free energy (⊿Gads) values, were calculated and discussed. To clarify inhibition mechanism, the synergistic effect of iodide ion was also investigated. The potential of zero charge (PZC) of the MS was studied by electrochemical impedance spectroscopy method, and a mechanism of adsorption process was proposed. It was demonstrated that inhibition efficiency increased with the increase in TCDI concentration and synergistically increased in the presence of KI. The inhibition efficiency was discussed in terms of adsorption of inhibitor molecules on the metal surface and protective filmformation.
The inhibition effect of 1,1’-thiocarbonyldiimidazole (TCDI) on the corrosion behaviors of mild steel (MS) in 0.5 mol·L -1 H2SO4 solution was studied with the help of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) techniques. The effect of immersion time on the inhibition effect of TCDI was also investigated over 72 h. For the long-term tests, hydrogen evolution with immersion time (VH2-t) was measured in addition to the three techniques already mentioned. The thermodynamic parameters, such as adsorption equilibrium constant (Kads) and adsorption free energy (⊿Gads) values, were calculated and discussed. To clarify inhibition mechanism, the synergistic effect of iodide ion was also investigated. The potential of zero charge (PZC) of the MS was studied by electrochemical impedance spectroscopy method, and a mechanism of adsorption process was proposed. It was demonstrated that inhibition efficiency increased with the increase in TCDI concentration and synergistically increased in the presence of KI. The inhibition efficiency was discussed in terms of adsorption of inhibitor molecules on the metal surface and protective filmformation.
2008, 24(07): 1192-1198
doi: 10.3866/PKU.WHXB20080713
Abstract:
High-crystallized β-zeolites with different silica-alumina molar ratios were successfully synthesized in extremely dense aqueous system using tetraethylammonium hydroxide (TEAOH) as template and solid silica gel as silica source, respectively. The silica-alumina molar ratios in the initial gels were 30, 60, 150, 300, 500, and pure silica, respectively, which were consistent with those in so-prepared samples determined by chemical method and XRF analysis. Subsequently, the physicochemical properties of samples were characterized by XRD, FT-IR, SEM, NH3-TPD, and N2-adsorption analysis. The results showed that the extent of dealumination was changed obviously and the acid content was decreased significantly in the low silica β-zeolite with highest aluminium content after hydrothermal treatment. The high silica or pure silica β-zeolites could not display higher hydrothermal stability partly due to their small grain sizes. After hydrothermal treatment, the medium silica-alumina ratio zeolite beta could remain higher acid amount and showed better hydrothermal stability. The effect of β-zeolites with different n(SiO2)/n(Al2O3) ratios as an active additive on cracking performance has been investigated. It was found that β-zeolite could increase the activity of cracking catalyst and improve the performance of resistance to carbon deposition. As β-zeolite with n(SiO2)/n(Al2O3) molar ratio of 150 was added, the cracking catalyst exhibited the higher cracking gasoline yield and lower carbon deposition.
High-crystallized β-zeolites with different silica-alumina molar ratios were successfully synthesized in extremely dense aqueous system using tetraethylammonium hydroxide (TEAOH) as template and solid silica gel as silica source, respectively. The silica-alumina molar ratios in the initial gels were 30, 60, 150, 300, 500, and pure silica, respectively, which were consistent with those in so-prepared samples determined by chemical method and XRF analysis. Subsequently, the physicochemical properties of samples were characterized by XRD, FT-IR, SEM, NH3-TPD, and N2-adsorption analysis. The results showed that the extent of dealumination was changed obviously and the acid content was decreased significantly in the low silica β-zeolite with highest aluminium content after hydrothermal treatment. The high silica or pure silica β-zeolites could not display higher hydrothermal stability partly due to their small grain sizes. After hydrothermal treatment, the medium silica-alumina ratio zeolite beta could remain higher acid amount and showed better hydrothermal stability. The effect of β-zeolites with different n(SiO2)/n(Al2O3) ratios as an active additive on cracking performance has been investigated. It was found that β-zeolite could increase the activity of cracking catalyst and improve the performance of resistance to carbon deposition. As β-zeolite with n(SiO2)/n(Al2O3) molar ratio of 150 was added, the cracking catalyst exhibited the higher cracking gasoline yield and lower carbon deposition.
2008, 24(07): 1199-1206
doi: 10.3866/PKU.WHXB20080714
Abstract:
Doped manganese oxide coating electrodes were prepared by pulse anodic electrodeposition. Their morphology, phase structure and electrochemical properties were studied by field emitted scanning electron microscopy (FESEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical methods. The results showed that electrodes with high electrocatalytic activity and stability could be produced by adjusting the pulse parameter. The deposition rate was high when pulse frequency (f) was 90 Hz and the pulse duty factor was 1:2. The oxide has a network structure mixed by nanowires and spherical nanoparticles, which can effectively improve the electrocatalytic activity and service life of these electrodes. The accelerated life of electrode was 1635 h, which was 55.3% higher than that of direct current electrodeposition.
Doped manganese oxide coating electrodes were prepared by pulse anodic electrodeposition. Their morphology, phase structure and electrochemical properties were studied by field emitted scanning electron microscopy (FESEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical methods. The results showed that electrodes with high electrocatalytic activity and stability could be produced by adjusting the pulse parameter. The deposition rate was high when pulse frequency (f) was 90 Hz and the pulse duty factor was 1:2. The oxide has a network structure mixed by nanowires and spherical nanoparticles, which can effectively improve the electrocatalytic activity and service life of these electrodes. The accelerated life of electrode was 1635 h, which was 55.3% higher than that of direct current electrodeposition.
2008, 24(07): 1207-1213
doi: 10.3866/PKU.WHXB20080715
Abstract:
The mechanisms of the reaction of peroxynitrous acid and tyrosine were studied using the density functional theory (DFT) at B3LYP/6-311G(d,p) level. The geometries of all the molecules were optimized; the harmonic vibration frequencies and the energies were calculated as well. The calculation results showed that stepwise mechanism rather than concerted mechanism was preferred for the reaction of peroxynitrous acid and tyrosine. The stepwise pathway started with homolysis of the HO—ONO bond to discrete·OH and·NO2 radicals, which then reacted with tyrosine via two different pathways: (i) the H atom of tyrosine hydroxyl was abstracted by·OH to produce IM3, which then combined with·NO2 forming the intermediate (IM1). Subsequently, the IM1 underwent further transformation leading to the product of 3-nitrotyrosine. (ii) the·OHwas added to the phenol ring of tyrosine to produce the IM2, which then combined with·NO2 forming the intermediate (IM21). The IM21 also underwent further transformation leading to the product of 3-hydroxytyrosine. The activation energies of the rate-determining steps of these two pathways were 82.86 and 48.05 kJ·mol-1, respectively. This conclusion was in od agreement with the corresponding experimental data. Additionally, effects of aqueous solvation of water on this reaction were also investigated and the results indicated that the reaction preferably took place in water.
The mechanisms of the reaction of peroxynitrous acid and tyrosine were studied using the density functional theory (DFT) at B3LYP/6-311G(d,p) level. The geometries of all the molecules were optimized; the harmonic vibration frequencies and the energies were calculated as well. The calculation results showed that stepwise mechanism rather than concerted mechanism was preferred for the reaction of peroxynitrous acid and tyrosine. The stepwise pathway started with homolysis of the HO—ONO bond to discrete·OH and·NO2 radicals, which then reacted with tyrosine via two different pathways: (i) the H atom of tyrosine hydroxyl was abstracted by·OH to produce IM3, which then combined with·NO2 forming the intermediate (IM1). Subsequently, the IM1 underwent further transformation leading to the product of 3-nitrotyrosine. (ii) the·OHwas added to the phenol ring of tyrosine to produce the IM2, which then combined with·NO2 forming the intermediate (IM21). The IM21 also underwent further transformation leading to the product of 3-hydroxytyrosine. The activation energies of the rate-determining steps of these two pathways were 82.86 and 48.05 kJ·mol-1, respectively. This conclusion was in od agreement with the corresponding experimental data. Additionally, effects of aqueous solvation of water on this reaction were also investigated and the results indicated that the reaction preferably took place in water.
2008, 24(07): 1214-1218
doi: 10.3866/PKU.WHXB20080716
Abstract:
In order to understand the synergistic effects between dielectric barrier discharge (DBD) plasmas and catalysts, the interactions between DBD and NO or NO/O2 saturated CuZSM-5 have been studied by adsorption and temperature programmed desorption (TPD) techniques. The results demonstrated that NO adsorbed on the CuZSM-5 surface and NOx species adsorbed on Cu active sites could be partly desorbed by DBD plasmas. Nitrogen oxides could be formed by plasma-induced surface reactions. A small amount of N2O and O2 could be formed in the NO/N2 system, and a significant amount of NOx (N2O, NO2, and NO) was generated in the NO/O2/N2 system by interactions between DBD plasmas and NO or NO/O2 adsorbed CuZSM-5. NOx removal over CuZSM-5 was tested by means of CuZSM-5 with or without plasma-pretreatment. After CuZSM-5, which had showed lower activity, was pretreated by N2 flow or DBD plasmas, NOx conversions in NO/N2 were 30.3% and 46.7%, respectively. The corresponding NOx conversion over fresh CuZSM-5 catalyst was 39.2%in NO/N2. A comparison of TPD profiles of NO and O2 over CuZSM-5 with or without plasma-pretreatment reveled that the key of the enhancement of NOx conversion on CuZSM-5 was the removal of NOx species present at Cu site by plasma-pretreating CuZSM-5.
In order to understand the synergistic effects between dielectric barrier discharge (DBD) plasmas and catalysts, the interactions between DBD and NO or NO/O2 saturated CuZSM-5 have been studied by adsorption and temperature programmed desorption (TPD) techniques. The results demonstrated that NO adsorbed on the CuZSM-5 surface and NOx species adsorbed on Cu active sites could be partly desorbed by DBD plasmas. Nitrogen oxides could be formed by plasma-induced surface reactions. A small amount of N2O and O2 could be formed in the NO/N2 system, and a significant amount of NOx (N2O, NO2, and NO) was generated in the NO/O2/N2 system by interactions between DBD plasmas and NO or NO/O2 adsorbed CuZSM-5. NOx removal over CuZSM-5 was tested by means of CuZSM-5 with or without plasma-pretreatment. After CuZSM-5, which had showed lower activity, was pretreated by N2 flow or DBD plasmas, NOx conversions in NO/N2 were 30.3% and 46.7%, respectively. The corresponding NOx conversion over fresh CuZSM-5 catalyst was 39.2%in NO/N2. A comparison of TPD profiles of NO and O2 over CuZSM-5 with or without plasma-pretreatment reveled that the key of the enhancement of NOx conversion on CuZSM-5 was the removal of NOx species present at Cu site by plasma-pretreating CuZSM-5.
2008, 24(07): 1219-1224
doi: 10.3866/PKU.WHXB20080717
Abstract:
Clustered and flowerlike CdS nanostructures were synthesized via the controllable solvent thermal
method using ethylenediamine as the structure-directing template. The phase structures and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRDpatterns demonstrated that the CdS nanorod cluster sample was hexa nal cell and the flowerlike CdS nanostructure was cubic cell. Experimental results showed that the whole self-assembly process was made-up of nucleation and growth, which was due to the competition in the nucleation. And the template function of ethylenediamine played an important role in the self-assembly. The self-assembly mechanisms of forming the clustered and flowerlike nanostructures were investigated on the basis of the time-and temperature-dependent experiments and were briefly discussed. At room temperature, photoluminescence (PL) spectrum experiments revealed that CdS nanostructures had two visible emission peaks respectively at the wavelengths of 433 nm and nearly 565 nm, which should arise respectively from the excitonic emission and surface-defect. The specific surface areas were characterized by the Brunauer-Emmett-Teller (BET) method. The photocatalysis of clustered and flowerlike CdS nanostructures in methyl orange (MeO) under high-pressure mercury lamp illumination was investigated. The experimental results indicated that the performance of photocatalytic system employing flowerlike CdS nanostructure, with higher specific surface area, was observed to be better than other CdS materials.
Clustered and flowerlike CdS nanostructures were synthesized via the controllable solvent thermal
method using ethylenediamine as the structure-directing template. The phase structures and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRDpatterns demonstrated that the CdS nanorod cluster sample was hexa nal cell and the flowerlike CdS nanostructure was cubic cell. Experimental results showed that the whole self-assembly process was made-up of nucleation and growth, which was due to the competition in the nucleation. And the template function of ethylenediamine played an important role in the self-assembly. The self-assembly mechanisms of forming the clustered and flowerlike nanostructures were investigated on the basis of the time-and temperature-dependent experiments and were briefly discussed. At room temperature, photoluminescence (PL) spectrum experiments revealed that CdS nanostructures had two visible emission peaks respectively at the wavelengths of 433 nm and nearly 565 nm, which should arise respectively from the excitonic emission and surface-defect. The specific surface areas were characterized by the Brunauer-Emmett-Teller (BET) method. The photocatalysis of clustered and flowerlike CdS nanostructures in methyl orange (MeO) under high-pressure mercury lamp illumination was investigated. The experimental results indicated that the performance of photocatalytic system employing flowerlike CdS nanostructure, with higher specific surface area, was observed to be better than other CdS materials.
2008, 24(07): 1225-1232
doi: 10.3866/PKU.WHXB20080718
Abstract:
For many engineering applications, it is important to obtain reliable data of the solubility of air in dimethyl silicone and hydraulic oils. Overcoming some drawbacks of previous methods for measuring gas-solubility, a new piston apparatus was established, in which the state equation of ideal gas was used to determine the amount of gas-dissolution. An expression of the Bunsen solubility of air in 500cSt silicone at temperatures of 293.2 and 353.2 K and in the gas-pressure range of 0-350 kPa was determined. The Bunsen solubilities of air in 20cSt silicone and Chinese 32# hydraulic oils at 298.2 K under various gas-pressures were also measured. Reliability and accuracy analyses indicated that the error range of the experimental data was about 6%. The Bunsen solubility and gas-pressure exhibited od linearity, while the relationship between the molar fraction and the pressure in the experimental range was nonlinear but could be well fitted by the Krichevsky-Ilinskaya equation. It was discovered that the Bunsen solubilities of air in silicone with quite different molecular mass were close to each other. The results suggested that the molar fraction based on the monomer mass was more appropriate than that based on the molecular mass for engineering extrapolation of the solubility data of small and non-polar solutes in polymer solvents. At last, for solvents containing much different or uncertain molecular mass, the commonplace in engineering applications, the Bunsen solubility was appropriate to give the dissolved gas concentration.
For many engineering applications, it is important to obtain reliable data of the solubility of air in dimethyl silicone and hydraulic oils. Overcoming some drawbacks of previous methods for measuring gas-solubility, a new piston apparatus was established, in which the state equation of ideal gas was used to determine the amount of gas-dissolution. An expression of the Bunsen solubility of air in 500cSt silicone at temperatures of 293.2 and 353.2 K and in the gas-pressure range of 0-350 kPa was determined. The Bunsen solubilities of air in 20cSt silicone and Chinese 32# hydraulic oils at 298.2 K under various gas-pressures were also measured. Reliability and accuracy analyses indicated that the error range of the experimental data was about 6%. The Bunsen solubility and gas-pressure exhibited od linearity, while the relationship between the molar fraction and the pressure in the experimental range was nonlinear but could be well fitted by the Krichevsky-Ilinskaya equation. It was discovered that the Bunsen solubilities of air in silicone with quite different molecular mass were close to each other. The results suggested that the molar fraction based on the monomer mass was more appropriate than that based on the molecular mass for engineering extrapolation of the solubility data of small and non-polar solutes in polymer solvents. At last, for solvents containing much different or uncertain molecular mass, the commonplace in engineering applications, the Bunsen solubility was appropriate to give the dissolved gas concentration.
2008, 24(07): 1233-1238
doi: 10.3866/PKU.WHXB20080719
Abstract:
We have studied the structural, energetical, and electronic properties of CdxZn1 -xO films in wurtzite structure and CdO in rocksalt, zinc blende, and wurtzite structures by the method of total energy plane-wave expansion with first-principles ultrasoft pseudo-potential technology based on the density functional theory (DFT). Stabilities of CdO in different structures were analyzed and it was concluded that rocksalt and wurtzite structures of CdO almost had the same stability, but the zinc blende structure was not so stable. From the simulation of CdxZn1-xO films, we obtained the equilibrium lattice constants, the formation energies, and the band gap energy bowing parameter. The results of formation energies revealed that the CdxZn1-xOfilms were unstable at the composition of about x=0.4. Phase segregation between ZnO and CdO might occur at this point.
We have studied the structural, energetical, and electronic properties of CdxZn1 -xO films in wurtzite structure and CdO in rocksalt, zinc blende, and wurtzite structures by the method of total energy plane-wave expansion with first-principles ultrasoft pseudo-potential technology based on the density functional theory (DFT). Stabilities of CdO in different structures were analyzed and it was concluded that rocksalt and wurtzite structures of CdO almost had the same stability, but the zinc blende structure was not so stable. From the simulation of CdxZn1-xO films, we obtained the equilibrium lattice constants, the formation energies, and the band gap energy bowing parameter. The results of formation energies revealed that the CdxZn1-xOfilms were unstable at the composition of about x=0.4. Phase segregation between ZnO and CdO might occur at this point.
2008, 24(07): 1239-1244
doi: 10.3866/PKU.WHXB20080720
Abstract:
The inhibition performance of four corrosion inhibitors in HCl mild steel corrosions, including 2-mercaptobenzimidazole (A), 2-amidobenzimidazole (B), 2-methylbenzimidazole (C), and benzimidazole (D), was theoretically evaluated using quantum chemistry calculations and molecular dynamics simulations, and the corrosion inhibition mechanism was analyzed. Global activity indices indicated that 2-mercaptobenzimidazole bore the highest reaction activity among the four molecules. For the three other molecules, Fukui indices and total electron density distributions suggested that 2-amidobenzimidazole possessed two electrophilic attack centers, which enabled multi-center adsorption of the molecule on metal surfaces and thus had preferable corrosion inhibition performance compared to 2-methylbenzimidazole and benzimidazole. Molecular dynamics simulation results showed that 2-methylbenzimidazole was more stably adsorbed on the metal surfaces than benzimidazole did when the interaction of the inhibitor molecules with three layers of iron atoms was considered. With the help of the theoretical results, the efficiency order of the four inhibitors was found to be A>B>C>D, which accorded well with experimental results.
The inhibition performance of four corrosion inhibitors in HCl mild steel corrosions, including 2-mercaptobenzimidazole (A), 2-amidobenzimidazole (B), 2-methylbenzimidazole (C), and benzimidazole (D), was theoretically evaluated using quantum chemistry calculations and molecular dynamics simulations, and the corrosion inhibition mechanism was analyzed. Global activity indices indicated that 2-mercaptobenzimidazole bore the highest reaction activity among the four molecules. For the three other molecules, Fukui indices and total electron density distributions suggested that 2-amidobenzimidazole possessed two electrophilic attack centers, which enabled multi-center adsorption of the molecule on metal surfaces and thus had preferable corrosion inhibition performance compared to 2-methylbenzimidazole and benzimidazole. Molecular dynamics simulation results showed that 2-methylbenzimidazole was more stably adsorbed on the metal surfaces than benzimidazole did when the interaction of the inhibitor molecules with three layers of iron atoms was considered. With the help of the theoretical results, the efficiency order of the four inhibitors was found to be A>B>C>D, which accorded well with experimental results.
2008, 24(07): 1245-1251
doi: 10.3866/PKU.WHXB20080721
Abstract:
The reaction mechanism of CH3SH with radical CN·was investigated by using B3LYP method with 6-311++G(d,p) basis set, and three reaction channels were found. The geometries of the reactants, intermediates, transition states, and products were optimized. Stationary points of the reaction channels were confirmed by the intrinsic reaction coordinate (IRC) tracing. The energies of the species were corrected at CCSD/6-311++G(d,p) level. The calculated results successfully explained the conclusions of Brian’s experimental study. The cleavage and formation of the chemical bonds in the reaction process were discussed by the topological analysis of electronic density, and the transition state with six-member-ring structure (STS) was found.
The reaction mechanism of CH3SH with radical CN·was investigated by using B3LYP method with 6-311++G(d,p) basis set, and three reaction channels were found. The geometries of the reactants, intermediates, transition states, and products were optimized. Stationary points of the reaction channels were confirmed by the intrinsic reaction coordinate (IRC) tracing. The energies of the species were corrected at CCSD/6-311++G(d,p) level. The calculated results successfully explained the conclusions of Brian’s experimental study. The cleavage and formation of the chemical bonds in the reaction process were discussed by the topological analysis of electronic density, and the transition state with six-member-ring structure (STS) was found.
2008, 24(07): 1252-1256
doi: 10.3866/PKU.WHXB20080722
Abstract:
Geometry structures, electronic structures, and magnetic properties of (CoCr)n (n=1-5) clusters were systematically investigated by using density functional theory with generalized gradient approximation (GGA). The ground state and metastable state of clusters were confirmed. The research results indicated that geometric configurations of the ground state CoCr alloy clusters showed symmetry and ordered arrangement; magnetisms of alloy clusters all showed anti-ferromagnetic coupling, coordination number and bond length of CoCr alloy clusters had obvious influence on local magnetism; and due to the influence of chromium atom, in (CoCr)4 cluster, non-adjacent Co atoms presented anti-ferromagnetic coupling.
Geometry structures, electronic structures, and magnetic properties of (CoCr)n (n=1-5) clusters were systematically investigated by using density functional theory with generalized gradient approximation (GGA). The ground state and metastable state of clusters were confirmed. The research results indicated that geometric configurations of the ground state CoCr alloy clusters showed symmetry and ordered arrangement; magnetisms of alloy clusters all showed anti-ferromagnetic coupling, coordination number and bond length of CoCr alloy clusters had obvious influence on local magnetism; and due to the influence of chromium atom, in (CoCr)4 cluster, non-adjacent Co atoms presented anti-ferromagnetic coupling.
2008, 24(07): 1257-1263
doi: 10.3866/PKU.WHXB20080723
Abstract:
The optimized stable (CH3)2S…ClOH halogen bond and (CH3)2S…HOCl hydrogen bond complexes were found on the potential energy surface by means of DFT-B3LYP/6-311++G**. The obvious red shifts of the 10Cl—11O and 12H—11O stretching vibrational frequencies in the two complexes were obtained via frequency analysis. The halogen bond interaction energy of (CH3)2S…ClOH was -11.69 kJ·mol-1, and the hydrogen bond interaction energy of (CH3)2S…HOCl was -24.16 kJ·mol-1, which were calculated with basis set superposition error (BSSE) correction via counterpoise procedure (CP) method at MP2/6-311G** level. Natural bond orbital (NBO) theory analysis showed that two kinds of charge transfers existed in (CH3)2S…ClOH halogen bond system: (i) lone pair LP(1S)1→σ*(10Cl—11O); (ii) lone pair LP(1S)2→σ*(10Cl—11O), and the natural population of the σ*(10Cl—11O) increased by 0.14035e. Analo us charge transfers existed in (CH3)2S…HOCl hydrogen bond complex. Bond order analysis with natural resonance theory (NRT) showed that bond order of 10Cl—11O in (CH3)2S…ClOH halogen bond complex and bond order of 12H—11Oin (CH3)2S…HOCl hydrogen bond complex both decreased. The topological properties of the halogen bond and hydrogen bond structures were also investigated by the atoms-in-molecules (AIM) theory.
The optimized stable (CH3)2S…ClOH halogen bond and (CH3)2S…HOCl hydrogen bond complexes were found on the potential energy surface by means of DFT-B3LYP/6-311++G**. The obvious red shifts of the 10Cl—11O and 12H—11O stretching vibrational frequencies in the two complexes were obtained via frequency analysis. The halogen bond interaction energy of (CH3)2S…ClOH was -11.69 kJ·mol-1, and the hydrogen bond interaction energy of (CH3)2S…HOCl was -24.16 kJ·mol-1, which were calculated with basis set superposition error (BSSE) correction via counterpoise procedure (CP) method at MP2/6-311G** level. Natural bond orbital (NBO) theory analysis showed that two kinds of charge transfers existed in (CH3)2S…ClOH halogen bond system: (i) lone pair LP(1S)1→σ*(10Cl—11O); (ii) lone pair LP(1S)2→σ*(10Cl—11O), and the natural population of the σ*(10Cl—11O) increased by 0.14035e. Analo us charge transfers existed in (CH3)2S…HOCl hydrogen bond complex. Bond order analysis with natural resonance theory (NRT) showed that bond order of 10Cl—11O in (CH3)2S…ClOH halogen bond complex and bond order of 12H—11Oin (CH3)2S…HOCl hydrogen bond complex both decreased. The topological properties of the halogen bond and hydrogen bond structures were also investigated by the atoms-in-molecules (AIM) theory.
2008, 24(07): 1264-1270
doi: 10.3866/PKU.WHXB20080724
Abstract:
Electrochemical reduction characteristics of fumaric acid (FA) and maleic acid (MA) at lead electrode were investigated by voltammetry, chronocoulometry, and electrochemical impedance spectrum (EIS). The corresponding transfer coefficients, apparent energies of activation, and diffusion coefficients were calculated and the mechanism of electrochemical reduction were discussed. The experimental results showed that the electrochemical reduction of FA and MA was two-electron irreversible reaction, in which the diffusion process was the rate-determined step. The reductive potential of FA at lead was about 0.1 V higher than that of MA, indicating that FA is more difficult to be electroreduced. The corresponding diffusion coefficients for 0.04 mol·L-1 FA and MA in 0.1 mol·L-1 sulphuric acid solution were 7.96×10-6 and 6.72×10-6 cm2·s-1, respectively. The EIS results showed that charge transfer was the rate-determined step in the electroreduction processes of FA and MA at Pb electrode under low DC bias. As increase in bias potential, the diffusion process became the rate-determined step gradually. The difference in the electroreduction characteristics of FA and MA at Pb electrode was due to their different three-dimensional structure.
Electrochemical reduction characteristics of fumaric acid (FA) and maleic acid (MA) at lead electrode were investigated by voltammetry, chronocoulometry, and electrochemical impedance spectrum (EIS). The corresponding transfer coefficients, apparent energies of activation, and diffusion coefficients were calculated and the mechanism of electrochemical reduction were discussed. The experimental results showed that the electrochemical reduction of FA and MA was two-electron irreversible reaction, in which the diffusion process was the rate-determined step. The reductive potential of FA at lead was about 0.1 V higher than that of MA, indicating that FA is more difficult to be electroreduced. The corresponding diffusion coefficients for 0.04 mol·L-1 FA and MA in 0.1 mol·L-1 sulphuric acid solution were 7.96×10-6 and 6.72×10-6 cm2·s-1, respectively. The EIS results showed that charge transfer was the rate-determined step in the electroreduction processes of FA and MA at Pb electrode under low DC bias. As increase in bias potential, the diffusion process became the rate-determined step gradually. The difference in the electroreduction characteristics of FA and MA at Pb electrode was due to their different three-dimensional structure.
2008, 24(07): 1271-1276
doi: 10.3866/PKU.WHXB20080725
Abstract:
The decomposition of CF4 in the absence of water on γ-Al2O3-based metal oxides was carried out to destruct the disposal perfluoro-carbons (PFCs) from industrial processes. In the present work, the conversion of CF4 was tested over bare γ-Al2O3 at different temperatures of 825, 850 and 900 ℃. It was found that the initial activity of Al2O3 increased in the order of 825 ℃<850 ℃<900 ℃CO2 yield declined quickly with time on stream because the un-reacted γ-Al2O3 was transformed into inactive α-Al2O3 phase that resulted from the highly exothermic effect of Al2O3-fluorination reaction. As for the CF4 decomposition on M -Al2O3, fluorination of Mg species and the highly exothermic effect produced led to the collapse of MgAl2O4 structure, in which the magnesium element was fluorinated into MgF2. Al2O3 modified with P or Ni could inhibit the transformation of un-reacted γ-Al2O3 into α-Al2O3 during CF4 decomposition, and consequently CF4 conversion reached a stable level with time on stream.
The decomposition of CF4 in the absence of water on γ-Al2O3-based metal oxides was carried out to destruct the disposal perfluoro-carbons (PFCs) from industrial processes. In the present work, the conversion of CF4 was tested over bare γ-Al2O3 at different temperatures of 825, 850 and 900 ℃. It was found that the initial activity of Al2O3 increased in the order of 825 ℃<850 ℃<900 ℃CO2 yield declined quickly with time on stream because the un-reacted γ-Al2O3 was transformed into inactive α-Al2O3 phase that resulted from the highly exothermic effect of Al2O3-fluorination reaction. As for the CF4 decomposition on M -Al2O3, fluorination of Mg species and the highly exothermic effect produced led to the collapse of MgAl2O4 structure, in which the magnesium element was fluorinated into MgF2. Al2O3 modified with P or Ni could inhibit the transformation of un-reacted γ-Al2O3 into α-Al2O3 during CF4 decomposition, and consequently CF4 conversion reached a stable level with time on stream.
2008, 24(07): 1277-1282
doi: 10.3866/PKU.WHXB20080726
Abstract:
Semiconductor behavior of epoxy resin coated on carbon steel immersed in 0.5 mol·L-1 sulfuric acid aqueous solution during its degradation was investigated. Potential (U)-capacitance (C) measurement and Mott-Schottky analysis technology were utilized to understand the coat’s conduction mechanism during its degradation in the electrolyte. The epoxy resin film was still an insulator in the initial immersion stage (10 min), but its outer layer (the side that contacts with solution) gradually changed into n type semiconductor due to the corrosion with growing immersion time. Charge carrier density of this semiconductor film increased by degrees with extension of immersion time from 1010 cm-3 at 7 h to 1012 cm-3 at 48 h approximately. Between 7 h and 48 h, the organic film had not entirely transformed into semiconductor but only the outer side, and the inner was still insulator. Therefore, an MIS structure (metal-insulator-semiconductor) was generated. The result indicated that this MIS structure was in inversion state between -0.5 V and 0.5 V, and carrier charges were electron holes in inversion layer. The measured space-charge capacitance was series capacitance of inversion layer capacitance and depletion layer capacitance at relatively low frequency. The capacitance value decreased with growing polarization potential. The measured capacitance at relatively high frequency was only the depletion layer capacitance and remained constant in the total scanning potential region. An anodic drift occurred about the C-U characteristic curve of the MIS structure.
Semiconductor behavior of epoxy resin coated on carbon steel immersed in 0.5 mol·L-1 sulfuric acid aqueous solution during its degradation was investigated. Potential (U)-capacitance (C) measurement and Mott-Schottky analysis technology were utilized to understand the coat’s conduction mechanism during its degradation in the electrolyte. The epoxy resin film was still an insulator in the initial immersion stage (10 min), but its outer layer (the side that contacts with solution) gradually changed into n type semiconductor due to the corrosion with growing immersion time. Charge carrier density of this semiconductor film increased by degrees with extension of immersion time from 1010 cm-3 at 7 h to 1012 cm-3 at 48 h approximately. Between 7 h and 48 h, the organic film had not entirely transformed into semiconductor but only the outer side, and the inner was still insulator. Therefore, an MIS structure (metal-insulator-semiconductor) was generated. The result indicated that this MIS structure was in inversion state between -0.5 V and 0.5 V, and carrier charges were electron holes in inversion layer. The measured space-charge capacitance was series capacitance of inversion layer capacitance and depletion layer capacitance at relatively low frequency. The capacitance value decreased with growing polarization potential. The measured capacitance at relatively high frequency was only the depletion layer capacitance and remained constant in the total scanning potential region. An anodic drift occurred about the C-U characteristic curve of the MIS structure.
2008, 24(07): 1283-1286
doi: 10.3866/PKU.WHXB20080727
Abstract:
To enhance the absorption in the visible region for TiO2, C and/or N doping of TiO2 nanotube was carried out by a novel method——plasma electrolysis. The doping was achieved with active C and Nproduced fromthe plasma electrolysis of HCONH2, NaNO2, or (NH2)2CO. The results of XPS revealed that C and N were successfully doped into the lattice of TiO2. UV-Vis diffuse reflectance spectra showed a shift to longer wavelengths and an enhancement of the absorption in the visible region (>400 nm) for the C, N-codoped TiO2, compared to the pure TiO2, C-doped TiO2 and N-doped TiO2. The C, N-codoped TiO2 showed the best photocatalytic activities for the degradation of methyl orange under visible light irradiation, and was a promising photocatalyst for utilizing the solar energy.
To enhance the absorption in the visible region for TiO2, C and/or N doping of TiO2 nanotube was carried out by a novel method——plasma electrolysis. The doping was achieved with active C and Nproduced fromthe plasma electrolysis of HCONH2, NaNO2, or (NH2)2CO. The results of XPS revealed that C and N were successfully doped into the lattice of TiO2. UV-Vis diffuse reflectance spectra showed a shift to longer wavelengths and an enhancement of the absorption in the visible region (>400 nm) for the C, N-codoped TiO2, compared to the pure TiO2, C-doped TiO2 and N-doped TiO2. The C, N-codoped TiO2 showed the best photocatalytic activities for the degradation of methyl orange under visible light irradiation, and was a promising photocatalyst for utilizing the solar energy.
2008, 24(07): 1287-1291
doi: 10.3866/PKU.WHXB20080728
Abstract:
Nanostructured CuF2 thin films were prepared by pulsed laser deposition on stainless steel substrates. The charge and discharge curves showed a high reversible capacity of 540 mAh·g-1, corresponding to 2.0 Li per CuF2. The cyclic voltammograms showed that a new couple of reduction and oxidation peaks at 2.2 and 2.8 V (vs Li/Li+) appeared for the first time. The components and structure of the films after charging and discharging were characterized by ex-situ high-resolution transmission electron microscopy and selected area electron diffraction measurements. Electrochemical reaction mechanism of nanostructured CuF2 thin films with lithium was revealed, in which the reversible decomposition and formation of LiF driven by transition metal Cu were involved.
Nanostructured CuF2 thin films were prepared by pulsed laser deposition on stainless steel substrates. The charge and discharge curves showed a high reversible capacity of 540 mAh·g-1, corresponding to 2.0 Li per CuF2. The cyclic voltammograms showed that a new couple of reduction and oxidation peaks at 2.2 and 2.8 V (vs Li/Li+) appeared for the first time. The components and structure of the films after charging and discharging were characterized by ex-situ high-resolution transmission electron microscopy and selected area electron diffraction measurements. Electrochemical reaction mechanism of nanostructured CuF2 thin films with lithium was revealed, in which the reversible decomposition and formation of LiF driven by transition metal Cu were involved.
2008, 24(07): 1292-1296
doi: 10.3866/PKU.WHXB20080729
Abstract:
Zn-Cu alloy nanocomposites were prepared directly from Zn-Cu alloy wire (w(Zn)=0.65)) by wire electrical explosion (WEE) method. The average particle size was in the range of 60-90 nm. Subsequently, Zn-Cu nanoparticles were oxidized to form ZnO-CuO nanocomposites after calcination at 500 ℃ in air for 2 h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the structure and morphology of the ZnO-CuO nanocomposites. Furthermore, the ZnO-CuO nanocomposites were coated on the surface of a ceramic tube to fabricate thick filmgas sensors, which showed strong gas sensing activities to C2H5OH.
Zn-Cu alloy nanocomposites were prepared directly from Zn-Cu alloy wire (w(Zn)=0.65)) by wire electrical explosion (WEE) method. The average particle size was in the range of 60-90 nm. Subsequently, Zn-Cu nanoparticles were oxidized to form ZnO-CuO nanocomposites after calcination at 500 ℃ in air for 2 h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the structure and morphology of the ZnO-CuO nanocomposites. Furthermore, the ZnO-CuO nanocomposites were coated on the surface of a ceramic tube to fabricate thick filmgas sensors, which showed strong gas sensing activities to C2H5OH.
2008, 24(07): 1297-1301
doi: 10.3866/PKU.WHXB20080730
Abstract:
The catalytic properties of PtSn/γ-Al2O3, PtSn/MCM-41 and PtSn/Al2O3/MCM-41 catalysts for propane dehydrogenation were studied using microreactor tests combined with X-ray diffraction (XRD), BET surface area and pore structure measurements, temperature-programmed reduction (TPR), H2-chemisorption and thermogravimetric (TG) analysis. It was shown that the PtSn catalysts supported on Al2O3-modified MCM-41 (Al2O3/MCM-41) exhibited higher activity than the PtSn/MCM-41 catalyst, and higher catalytic stability than the conventional PtSn/γ-Al2O3 catalyst for propane dehydrogenation. The characterization results of the catalysts revealed that on the surface of pure MCM-41, the dispersed Sn species were easier to be reduced to metallic state due to weak interaction of Sn with MCM-41 support, resulting in lower Pt dispersity and thus lower catalytic activity. In contrast, modifying the surface of MCM-41 by alumina could enhance the interaction between Sn and Al2O3/MCM-41 support, and increase Pt dispersity and catalytic activity for propane dehydrogenation. Moreover, the PtSn/Al2O3/MCM-41 catalysts had larger bare fraction of Pt surface after coke deposition, leading to their higher catalytic stability than the PtSn/γ-Al2O3 catalyst. It is suggested that the unique catalytic properties of PtSn/Al2O3/MCM-41 catalysts are correlated not only to the strong interaction of Sn with Al2O3/MCM-41support but also to the mesoporous structure of the Al2O3/MCM-41 support.
The catalytic properties of PtSn/γ-Al2O3, PtSn/MCM-41 and PtSn/Al2O3/MCM-41 catalysts for propane dehydrogenation were studied using microreactor tests combined with X-ray diffraction (XRD), BET surface area and pore structure measurements, temperature-programmed reduction (TPR), H2-chemisorption and thermogravimetric (TG) analysis. It was shown that the PtSn catalysts supported on Al2O3-modified MCM-41 (Al2O3/MCM-41) exhibited higher activity than the PtSn/MCM-41 catalyst, and higher catalytic stability than the conventional PtSn/γ-Al2O3 catalyst for propane dehydrogenation. The characterization results of the catalysts revealed that on the surface of pure MCM-41, the dispersed Sn species were easier to be reduced to metallic state due to weak interaction of Sn with MCM-41 support, resulting in lower Pt dispersity and thus lower catalytic activity. In contrast, modifying the surface of MCM-41 by alumina could enhance the interaction between Sn and Al2O3/MCM-41 support, and increase Pt dispersity and catalytic activity for propane dehydrogenation. Moreover, the PtSn/Al2O3/MCM-41 catalysts had larger bare fraction of Pt surface after coke deposition, leading to their higher catalytic stability than the PtSn/γ-Al2O3 catalyst. It is suggested that the unique catalytic properties of PtSn/Al2O3/MCM-41 catalysts are correlated not only to the strong interaction of Sn with Al2O3/MCM-41support but also to the mesoporous structure of the Al2O3/MCM-41 support.
2008, 24(07): 1302-1306
doi: 10.3866/PKU.WHXB20080731
Abstract:
Et4NBF4/LiPF6-based electrolytes were investigated to study the effects of the electrolytes with blend solvent EC+PC+DMC on the interface characteristics of graphite electrode. Cyclic voltammetry (CV) and charge-discharge test were used to examine the compatibility between the electrolytes and graphite anode. FTIR spectroscopy was used to analyze the variational component of the solid electrolyte interface (SEI) film. The results showed that Et4NBF4 was concerned with the formation of SEI film. Irreversible capacity in the first circle remarkably reduced when the concentrations of Et4NBF4 were 0.2 and 0.5 mol·L-1, and the circle efficiencies rose to 76.0% and 81.6%, respectively. LiPF6/Et4NBF4 blend-salt electrolytes system can effectively improve the compatibility between PC-based electrolyte and graphite anode.
Et4NBF4/LiPF6-based electrolytes were investigated to study the effects of the electrolytes with blend solvent EC+PC+DMC on the interface characteristics of graphite electrode. Cyclic voltammetry (CV) and charge-discharge test were used to examine the compatibility between the electrolytes and graphite anode. FTIR spectroscopy was used to analyze the variational component of the solid electrolyte interface (SEI) film. The results showed that Et4NBF4 was concerned with the formation of SEI film. Irreversible capacity in the first circle remarkably reduced when the concentrations of Et4NBF4 were 0.2 and 0.5 mol·L-1, and the circle efficiencies rose to 76.0% and 81.6%, respectively. LiPF6/Et4NBF4 blend-salt electrolytes system can effectively improve the compatibility between PC-based electrolyte and graphite anode.
2008, 24(07): 1307-1312
doi: 10.3866/PKU.WHXB20080732
Abstract:
Micromachining of magnesium alloy by confined etchant layer technique (CELT) was investigated. The variation of hydrogen ion concentration on the electrode surface during the electrochemical process was explored for some thermodynamically available“etchant-scavenger”systems, and their corrosion rate to magnesium alloy was measured. An effective electrochemistry“etching-scavenging”system was selected. Using NaNO2 as precursor for electrochemically generating etchant HNO3, NaOH as scavenger, and small amount of Na2SiO3 as inhibitor, 3-D microstructure lattice on a mold was replicated onto the magnesium alloy surface. The microstructures processed were approximately the negative copy of the ones on the mold. Sub-micrometer scale resolution was reached. The result suggested that CELT could be applied to machine the 3-D microstructure on magnesium alloy surface, which had potential to be used for the fabrication of micro electromechanical systems (MEMS).
Micromachining of magnesium alloy by confined etchant layer technique (CELT) was investigated. The variation of hydrogen ion concentration on the electrode surface during the electrochemical process was explored for some thermodynamically available“etchant-scavenger”systems, and their corrosion rate to magnesium alloy was measured. An effective electrochemistry“etching-scavenging”system was selected. Using NaNO2 as precursor for electrochemically generating etchant HNO3, NaOH as scavenger, and small amount of Na2SiO3 as inhibitor, 3-D microstructure lattice on a mold was replicated onto the magnesium alloy surface. The microstructures processed were approximately the negative copy of the ones on the mold. Sub-micrometer scale resolution was reached. The result suggested that CELT could be applied to machine the 3-D microstructure on magnesium alloy surface, which had potential to be used for the fabrication of micro electromechanical systems (MEMS).
2008, 24(07): 1313-1315
doi: 10.3866/PKU.WHXB20080733
Abstract:
The N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy=4,4’-dicarboxy-2,2’-bipyridyl), was demonstrated to be a highly selective luminescent and ratiocolorimetric sensors towards fluoride ion over chloride and bromide ions, by means of UV-Vis absorption and emission spectrophotometric titration method in dimethyl sulfoxide(DMSO) solution. Alarge“turn on”emission enhancement factor of 40, observed by the interaction of the N3 with fluoride ion was rather rare among the rutheniumcomplex-based fluoride ion sensors reported to date.
The N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy=4,4’-dicarboxy-2,2’-bipyridyl), was demonstrated to be a highly selective luminescent and ratiocolorimetric sensors towards fluoride ion over chloride and bromide ions, by means of UV-Vis absorption and emission spectrophotometric titration method in dimethyl sulfoxide(DMSO) solution. Alarge“turn on”emission enhancement factor of 40, observed by the interaction of the N3 with fluoride ion was rather rare among the rutheniumcomplex-based fluoride ion sensors reported to date.
2008, 24(07): 1316-1320
doi: 10.3866/PKU.WHXB20080734
Abstract:
The dilution enthalpies of N,N-dimethylformamide (DMF) in pure water and aqueous sodium chloride solutions were determined by using flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients in the range of sodium chloride concentration from 0 to 0.6 mol·kg-1 were calculated according to the McMillan-Mayer theory. It was found that enthalpic pairwise interaction coefficients (h2) of DMF were all positive in aqueous sodium chloride solutions and became larger with increasing the concentration of sodium chloride. The results were discussed in terms of the solute-solute and solute-solvent interactions.
2008, 24(07): 1321-1325
doi: 10.3866/PKU.WHXB20080735
Abstract:
A novel real-time measurement method to determine the refractive index and the thickness of a polymer film during photobleaching process was proposed based on the non-scanning attenuated total reflection (ATR) technique. Several dark lines corresponding to the guided-wave modes were demonstrated on the computer screen by a CCD camera. According to the shift of the dark lines, the changing values of refractive index and thickness of the polymer film can be simultaneously determined in time during photobleaching process. And we found that both chemical and physical change processes existed in the changes of refractive index and thickness of the polymer.
A novel real-time measurement method to determine the refractive index and the thickness of a polymer film during photobleaching process was proposed based on the non-scanning attenuated total reflection (ATR) technique. Several dark lines corresponding to the guided-wave modes were demonstrated on the computer screen by a CCD camera. According to the shift of the dark lines, the changing values of refractive index and thickness of the polymer film can be simultaneously determined in time during photobleaching process. And we found that both chemical and physical change processes existed in the changes of refractive index and thickness of the polymer.
2008, 24(07): 1326-1328
doi: 10.3866/PKU.WHXB20080736
Abstract:
Lithium iron phosphate powders were prepared by hydrothermal synthesis, and coated using glucose as carbon precursor. The contact angles for calculating surface free energy of LiFePO4 powders with three probe liquids were measured. The surface free energy and its dispersive part and polar part were calculated, based on Young equation and the method suggested by Wu. The relations of surface free energy to conductivity, coating property and specific capacity were studied. The results indicated that with the same conductivity, the dispersive/polar ratio of surface free energies (SE) of the powders had no effect on lowrate discharge capability, whereas had great effect on high rate discharge capability. The higher temperature and longer time of pyrolytic reaction led to an increase of the dispersive/polar ratio, which was beneficial for its adhesion with polyvinylidene fluoride (PVdF) and the enhancement of high rate discharge capability.
Lithium iron phosphate powders were prepared by hydrothermal synthesis, and coated using glucose as carbon precursor. The contact angles for calculating surface free energy of LiFePO4 powders with three probe liquids were measured. The surface free energy and its dispersive part and polar part were calculated, based on Young equation and the method suggested by Wu. The relations of surface free energy to conductivity, coating property and specific capacity were studied. The results indicated that with the same conductivity, the dispersive/polar ratio of surface free energies (SE) of the powders had no effect on lowrate discharge capability, whereas had great effect on high rate discharge capability. The higher temperature and longer time of pyrolytic reaction led to an increase of the dispersive/polar ratio, which was beneficial for its adhesion with polyvinylidene fluoride (PVdF) and the enhancement of high rate discharge capability.
