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1991 Volume 7 Issue 6
1991, 7(06): 641-645
doi: 10.3866/PKU.WHXB19910601
Abstract:
In comparison with the structure of hole-doped T phase (La_(2-x)Sr_x)CuO_4, electron-doped superconductors (Ln_(1.85)Ce_(0.15))CuO_(4-y), Ln=Pr, Nd, Sm, Eu, possess T phase structure with tetra nal I4/mmm symmetry. Their structural features are that the Cu ion is coordinated by four oxygen ions in square planar form and the Ln ion is located in octa-coordinate cubic site in the fluorite type LnO_2Ln duble layers. In this paper, the effects of preparation condition and cation substitution on the structure and superconductivity have been studied. Average ionic radius of Ln-site is limited in very narrow range. It can be changed by the substitution of larger or smaller ions. Its dimension is very important for structural type, structural stability under N_2 atmosphere and superconductivity.
In comparison with the structure of hole-doped T phase (La_(2-x)Sr_x)CuO_4, electron-doped superconductors (Ln_(1.85)Ce_(0.15))CuO_(4-y), Ln=Pr, Nd, Sm, Eu, possess T phase structure with tetra nal I4/mmm symmetry. Their structural features are that the Cu ion is coordinated by four oxygen ions in square planar form and the Ln ion is located in octa-coordinate cubic site in the fluorite type LnO_2Ln duble layers. In this paper, the effects of preparation condition and cation substitution on the structure and superconductivity have been studied. Average ionic radius of Ln-site is limited in very narrow range. It can be changed by the substitution of larger or smaller ions. Its dimension is very important for structural type, structural stability under N_2 atmosphere and superconductivity.
1991, 7(06): 646-647
doi: 10.3866/PKU.WHXB19910602
Abstract:
Both positive and negative phosphrus cluster ions were generated on a homemade laser-probe time-of-flight mass spectrometer. P_6~+ has the highest intensity in positive ion mass spectrum, and P_5~- for negative ions. It is proposed that both P_6~+ and P_5~- adopt the planar monocyclic configuration and are aromatic according to Hückel Rule. Further analysis of mass spectra shows that all cluster anions are composed of 5-membered rings and cations arc composed of 6-membered rings.
Both positive and negative phosphrus cluster ions were generated on a homemade laser-probe time-of-flight mass spectrometer. P_6~+ has the highest intensity in positive ion mass spectrum, and P_5~- for negative ions. It is proposed that both P_6~+ and P_5~- adopt the planar monocyclic configuration and are aromatic according to Hückel Rule. Further analysis of mass spectra shows that all cluster anions are composed of 5-membered rings and cations arc composed of 6-membered rings.
1991, 7(06): 648-650
doi: 10.3866/PKU.WHXB19910603
Abstract:
Chemical experiments and XPS analysis indicate that YBCO superconductor is a relatively strong base, and Ba-O components in YBCO is primarily responsible for its hasicity. Based on the basic property of YBCO, it is suggested that the chemical interactions between YBCO and oxide substrate materials is primarily solid acid-base reactions. The acid-base parameters for substrate materials (M , ZrO_2, Al_2O_3 and SiO_2) are calculated and used as a scale for measuring the acidity or basicity of the oxide substrates and for evaluating the YBCO-substrates chemical reactivity. It is found that the chemical reactivity increases with increasing acid-base parameter (or increases with increasing acidity) of the substrate materials. Therefore the chemical reactivity with YBCO increases in the order of M <ZrO_2<Al_2O_3<SiO_2.
The above rule is also suitable for chemical reaction of BSCCO superconductor with oxide substrate materials.
Chemical experiments and XPS analysis indicate that YBCO superconductor is a relatively strong base, and Ba-O components in YBCO is primarily responsible for its hasicity. Based on the basic property of YBCO, it is suggested that the chemical interactions between YBCO and oxide substrate materials is primarily solid acid-base reactions. The acid-base parameters for substrate materials (M , ZrO_2, Al_2O_3 and SiO_2) are calculated and used as a scale for measuring the acidity or basicity of the oxide substrates and for evaluating the YBCO-substrates chemical reactivity. It is found that the chemical reactivity increases with increasing acid-base parameter (or increases with increasing acidity) of the substrate materials. Therefore the chemical reactivity with YBCO increases in the order of M <ZrO_2<Al_2O_3<SiO_2.
The above rule is also suitable for chemical reaction of BSCCO superconductor with oxide substrate materials.
1991, 7(06): 651-654
doi: 10.3866/PKU.WHXB19910604
Abstract:
1991, 7(06): 655-661
doi: 10.3866/PKU.WHXB19910605
Abstract:
Monodispersed colloidal YOHCO_3·H_2O and Y_2O_3 systems consisting of spherical particles of narrow size distribution were obtained. The formation of those monodispersed colloidal systems was primarily investigated by using the techniques including transmision and scanning electron mieroseopy,IR spectroscopy and electrical conductivity. The change of electrical conductivity in the course of aging YCl_3 solution with urea revealed that the slow decomposition of urea and release of CO_3~(2-) at elevated temperature controlled the generation of pricipitation phase and provided necessary condition for formation of the monodispersed system.
The transformation of calcining monodispersed powders of YOHCO_3·H_2O was observed through SEM. During the process of calcining YOHCO_3·H_2O at 850 ℃, the powders were melten first before formation of monodispersed spheres of Y_2O_3.
Monodispersed colloidal YOHCO_3·H_2O and Y_2O_3 systems consisting of spherical particles of narrow size distribution were obtained. The formation of those monodispersed colloidal systems was primarily investigated by using the techniques including transmision and scanning electron mieroseopy,IR spectroscopy and electrical conductivity. The change of electrical conductivity in the course of aging YCl_3 solution with urea revealed that the slow decomposition of urea and release of CO_3~(2-) at elevated temperature controlled the generation of pricipitation phase and provided necessary condition for formation of the monodispersed system.
The transformation of calcining monodispersed powders of YOHCO_3·H_2O was observed through SEM. During the process of calcining YOHCO_3·H_2O at 850 ℃, the powders were melten first before formation of monodispersed spheres of Y_2O_3.
1991, 7(06): 662-665
doi: 10.3866/PKU.WHXB19910606
Abstract:
It was identified by many techniques such as XRD, IR, XPS, ESR and magnetic susceptibility measurement that the hetero-atoms on the frameworks of M-ZSM-48 type molecular sieves reside at the sites of distorted tetrahedral coordination. V and Cr exist as V(Ⅳ) and Cr(Ⅲ) respectively.
It was identified by many techniques such as XRD, IR, XPS, ESR and magnetic susceptibility measurement that the hetero-atoms on the frameworks of M-ZSM-48 type molecular sieves reside at the sites of distorted tetrahedral coordination. V and Cr exist as V(Ⅳ) and Cr(Ⅲ) respectively.
1991, 7(06): 666-672
doi: 10.3866/PKU.WHXB19910607
Abstract:
The effect of micelle on crystallization behaviour of dilute poly(methyl methacrylate-b-tetrahydrofuran) diblock copolymer/tetrahydrofuran homopolymer, dilute poly (ethylene-b-styrene-b-ethylene) triblock copolymer/ethylene homopolymer solutions has been studied. The results show that with the structural teansitions from spherical to nonspherical micelle in the blends, great changes in the nucleation and spherulite morphologies take place.
The effect of micelle on crystallization behaviour of dilute poly(methyl methacrylate-b-tetrahydrofuran) diblock copolymer/tetrahydrofuran homopolymer, dilute poly (ethylene-b-styrene-b-ethylene) triblock copolymer/ethylene homopolymer solutions has been studied. The results show that with the structural teansitions from spherical to nonspherical micelle in the blends, great changes in the nucleation and spherulite morphologies take place.
1991, 7(06): 673-680
doi: 10.3866/PKU.WHXB19910608
Abstract:
IR-spectroscopy and chemisorption in accompanying with CO, NO, H_2, O_2 as probe molecules have been used to elucidate the function of cobalt and ruthenium in the reduced Co-Mo/Al_2O_3, Ru-Mo/Al_2O_3, Ru-Co-Mo/Al_2O_3 catalysts. It is found, the location of cobalt has a partial block effect on Mo sites in its low oxidation state for adsorbing CO, NO, H_2, O_2 probes on reduced Co-Mo/Al_2O_3 catalysts, the intensities of CO and NO bands on Co sites are increased and the NO bands are shifted to the higher freqency side by about 20 cm~(-1) in comparing with that on Co/Al_2O_3 catalysts. In contrast to cobalt, uptake of CO, NO, H_2, O_2 probes are increased evidently on the Mo sitesin the coordination unsaturated state with the addition of ruthenium in the Ru-Mo/Al_2O_3 and Ru-Co-Mo/Al_2O_3 catalysts. It is suggested that ruthenium can promote the dissociation of hydrogen and the spilling of active hydrogen over Mo sites, which will be beneficial to the formation of more coordination unsaturated Mo sites.
IR-spectroscopy and chemisorption in accompanying with CO, NO, H_2, O_2 as probe molecules have been used to elucidate the function of cobalt and ruthenium in the reduced Co-Mo/Al_2O_3, Ru-Mo/Al_2O_3, Ru-Co-Mo/Al_2O_3 catalysts. It is found, the location of cobalt has a partial block effect on Mo sites in its low oxidation state for adsorbing CO, NO, H_2, O_2 probes on reduced Co-Mo/Al_2O_3 catalysts, the intensities of CO and NO bands on Co sites are increased and the NO bands are shifted to the higher freqency side by about 20 cm~(-1) in comparing with that on Co/Al_2O_3 catalysts. In contrast to cobalt, uptake of CO, NO, H_2, O_2 probes are increased evidently on the Mo sitesin the coordination unsaturated state with the addition of ruthenium in the Ru-Mo/Al_2O_3 and Ru-Co-Mo/Al_2O_3 catalysts. It is suggested that ruthenium can promote the dissociation of hydrogen and the spilling of active hydrogen over Mo sites, which will be beneficial to the formation of more coordination unsaturated Mo sites.
1991, 7(06): 681-687
doi: 10.3866/PKU.WHXB19910609
Abstract:
The mechanism of syngas conversion to ethanol over promoted Rhodium catalyst has been studied by in-situ chemical trapping reaction technique with CH_3OD as trapping agent. After trapping reaction, the products CH_3COOCH_3 and CH_2DCOOCH_3 were identified, which indicated the existence of ketene and acetyl intermediates in the ethanol synthesis reaction. With high CH_3OD/H_2 ratio in the feed (e.g., 18/5), more than 50% of CH_2DCOOCH_3 in total AcOMe was obtained, showing the acetyl intermediate is mainly derived from the tetene by further hydrogenation.
In order to further study ethanol formation mechanism in-situ chemical trapping reaction and isotopic exchange reaction of oxygen with D_2~(18)O as trapping and isotopic exchange agent was conducted. As for trapping reaction with D_2~(18)O, after trapping reaction and scanvenging with methanol in N_2 stream four kinds of methyl acetate, i.e., CH_2H(D)COOCH_3, CH_2H(D)C~(18)OOCH_3 were detected, again proving the existence of ketene and acetyl intermediates. As for isotopec exchange reaction of oxygen with D_2~(18)O, after this reaction and scanvenging with methanol in N_2 stream compounds including CH_3CH_2~(18)OH, CH_3CH~(18)O, and CH_2H(D)C~(18)OOCH_3 were formed, in which exchange of oxygen between D_2~(18)O and the ~(16)O-containing precursors of ethanol such as ketene, acetyl, and adsorbed acetaldehyde. Based on the mode of isotopic exchange of ketene with water produced in the syngas reaction, the isotopic distribution of ethanol in Tabeuchi and Katzer's experiment conducted with ~(13)C~(16)O/~(12)C~(18)O-H_2 could also be obtained by statistic calculation without the hypothesis proposed by Takeuchi and Katzer.
These results support the ketene mechanism, "CO-metalloxycarbene-carbene-ketene-acetyl-ethanol; (acetaldehyde)", proposed by us previously.
The mechanism of syngas conversion to ethanol over promoted Rhodium catalyst has been studied by in-situ chemical trapping reaction technique with CH_3OD as trapping agent. After trapping reaction, the products CH_3COOCH_3 and CH_2DCOOCH_3 were identified, which indicated the existence of ketene and acetyl intermediates in the ethanol synthesis reaction. With high CH_3OD/H_2 ratio in the feed (e.g., 18/5), more than 50% of CH_2DCOOCH_3 in total AcOMe was obtained, showing the acetyl intermediate is mainly derived from the tetene by further hydrogenation.
In order to further study ethanol formation mechanism in-situ chemical trapping reaction and isotopic exchange reaction of oxygen with D_2~(18)O as trapping and isotopic exchange agent was conducted. As for trapping reaction with D_2~(18)O, after trapping reaction and scanvenging with methanol in N_2 stream four kinds of methyl acetate, i.e., CH_2H(D)COOCH_3, CH_2H(D)C~(18)OOCH_3 were detected, again proving the existence of ketene and acetyl intermediates. As for isotopec exchange reaction of oxygen with D_2~(18)O, after this reaction and scanvenging with methanol in N_2 stream compounds including CH_3CH_2~(18)OH, CH_3CH~(18)O, and CH_2H(D)C~(18)OOCH_3 were formed, in which exchange of oxygen between D_2~(18)O and the ~(16)O-containing precursors of ethanol such as ketene, acetyl, and adsorbed acetaldehyde. Based on the mode of isotopic exchange of ketene with water produced in the syngas reaction, the isotopic distribution of ethanol in Tabeuchi and Katzer's experiment conducted with ~(13)C~(16)O/~(12)C~(18)O-H_2 could also be obtained by statistic calculation without the hypothesis proposed by Takeuchi and Katzer.
These results support the ketene mechanism, "CO-metalloxycarbene-carbene-ketene-acetyl-ethanol; (acetaldehyde)", proposed by us previously.
1991, 7(06): 688-693
doi: 10.3866/PKU.WHXB19910610
Abstract:
The activity coefficients and sahing-out constants of o-, m-, p-xylenes in six aqueous salt solutions at 25 ℃ are determined by spectrophotometric method. The salts used are Na_2SO_4, K_2SO_4, (NH_4)_2SO_4, MgSO_4 and MgCl_2. The relations logf-c_s are found to he all straight lines through the origin, in agreement with the Setschenow empirical formula. The order of salting-out ability is Na_2SO_4>K_2SO_4>(NH_4)_2SO_4>MgSO_4>MgCl_2
The experimental results of three xylenes are compared respectively with the calculated results of Debye-MacAulay and Conway-Desnoyers-Smith electrostatic theories, Masterton-Lee scaled particle theory and McDevit-Long internal pressure theory and internal pressure theory modified by Xie. The numerical calculation of the modified internal pressure theory agree with experimental data better.
The activity coefficients and sahing-out constants of o-, m-, p-xylenes in six aqueous salt solutions at 25 ℃ are determined by spectrophotometric method. The salts used are Na_2SO_4, K_2SO_4, (NH_4)_2SO_4, MgSO_4 and MgCl_2. The relations logf-c_s are found to he all straight lines through the origin, in agreement with the Setschenow empirical formula. The order of salting-out ability is Na_2SO_4>K_2SO_4>(NH_4)_2SO_4>MgSO_4>MgCl_2
The experimental results of three xylenes are compared respectively with the calculated results of Debye-MacAulay and Conway-Desnoyers-Smith electrostatic theories, Masterton-Lee scaled particle theory and McDevit-Long internal pressure theory and internal pressure theory modified by Xie. The numerical calculation of the modified internal pressure theory agree with experimental data better.
1991, 7(06): 694-698
doi: 10.3866/PKU.WHXB19910611
Abstract:
A new polynuclear silver complex with bridging diphorsphine ligand has been synthesized and characterized by :single cryatsl X-ray diffraction method The compound crystallizes in the triclinic space group P1 with a=1.27489, b=1.34715, c=1.47015 nm; α=59.747, β=63.949, γ=70.196°; V=1.9369 nm. The simplest formularis [Ag_4· dppe)_3(NO_3)_4], Mr=1874.79, D_c=1.607 g·cm~(-3), Dm=1.62 g·cm~(-3), μ(MoKa)=11.69 cm~(-1), F(OOO)=942. The structure was solved by conventional heavy-atom techniques and refined by full-matrix least squares to give discrepany indices of R=0.048 and RW=0.060(W=1/[σ(Fo)~2+(PWT*Fo)~2+QWT]-Fo) for 5052 reflections. An empirical absorption correction program DIFABS was performed.
Silver atoms are linked by bridging ligands of dppe and nitrate, forming a network extending in space. Each structural unit contains two binuclear subunits, of which silver atoms are bridged by nitrates. The two subunits are connected by one dppe ligand. Silver atoms are not equivalent in subunit and one of the nitrates functions not only as a monodentate bridging ligand, but also as an asymmetric bidentate chelating lingand. All coordinate configurations of silver are shown as distorted tetrahedron.
A new polynuclear silver complex with bridging diphorsphine ligand has been synthesized and characterized by :single cryatsl X-ray diffraction method The compound crystallizes in the triclinic space group P1 with a=1.27489, b=1.34715, c=1.47015 nm; α=59.747, β=63.949, γ=70.196°; V=1.9369 nm. The simplest formularis [Ag_4· dppe)_3(NO_3)_4], Mr=1874.79, D_c=1.607 g·cm~(-3), Dm=1.62 g·cm~(-3), μ(MoKa)=11.69 cm~(-1), F(OOO)=942. The structure was solved by conventional heavy-atom techniques and refined by full-matrix least squares to give discrepany indices of R=0.048 and RW=0.060(W=1/[σ(Fo)~2+(PWT*Fo)~2+QWT]-Fo) for 5052 reflections. An empirical absorption correction program DIFABS was performed.
Silver atoms are linked by bridging ligands of dppe and nitrate, forming a network extending in space. Each structural unit contains two binuclear subunits, of which silver atoms are bridged by nitrates. The two subunits are connected by one dppe ligand. Silver atoms are not equivalent in subunit and one of the nitrates functions not only as a monodentate bridging ligand, but also as an asymmetric bidentate chelating lingand. All coordinate configurations of silver are shown as distorted tetrahedron.
1991, 7(06): 699-702
doi: 10.3866/PKU.WHXB19910612
Abstract:
Spindal, star-shaped and bipyramidal monodispersed particles of Fe_2O_3 were prepared from solutions of Fe(NO_3)_3 by using the simplified procedures under general experimental conditions.The concentration and pH domains for the preparation of these monodispersed systems have been given. One of the important factors which affect the shape of pricipited particles formed at elevated temperature is pH value in the initial solution. The transformation of particles in various shapes were observed by using an electron microscope. The obtained results will be helpfull to preparation in a large scale and practical application of the monodispersed systems.
Spindal, star-shaped and bipyramidal monodispersed particles of Fe_2O_3 were prepared from solutions of Fe(NO_3)_3 by using the simplified procedures under general experimental conditions.The concentration and pH domains for the preparation of these monodispersed systems have been given. One of the important factors which affect the shape of pricipited particles formed at elevated temperature is pH value in the initial solution. The transformation of particles in various shapes were observed by using an electron microscope. The obtained results will be helpfull to preparation in a large scale and practical application of the monodispersed systems.
1991, 7(06): 703-707
doi: 10.3866/PKU.WHXB19910613
Abstract:
The measurements of low angle X-ray diffraction showed that the degression of d_0 of lamellar liquid crystal with increase of weight ratio of C_nOH/SDS decreased with increase of the carbon chain length of alcohol used aseosurfactant. The values of d_0 increased with carbon number of alcohol n at certain weight ratio of C_nOH/SDS. The increase of interlayer spacing d with n was related with the increase of d_0 and the decrease of solvent penetration in lamellar liquid crystal under the conditione of weight ratio of C_nOH/SDS and water content. Both the measurements of low angle X-ray diffraction and the phase diagram behavior showed that the stability of lamellar liquid crystal increased with the chain length of alcohol.
The measurements of low angle X-ray diffraction showed that the degression of d_0 of lamellar liquid crystal with increase of weight ratio of C_nOH/SDS decreased with increase of the carbon chain length of alcohol used aseosurfactant. The values of d_0 increased with carbon number of alcohol n at certain weight ratio of C_nOH/SDS. The increase of interlayer spacing d with n was related with the increase of d_0 and the decrease of solvent penetration in lamellar liquid crystal under the conditione of weight ratio of C_nOH/SDS and water content. Both the measurements of low angle X-ray diffraction and the phase diagram behavior showed that the stability of lamellar liquid crystal increased with the chain length of alcohol.
1991, 7(06): 708-711
doi: 10.3866/PKU.WHXB19910614
Abstract:
A simple chemical method for preparing SERS active surfaces was developed by etching silver foils in concentrated HNO_3 solutions. The enhancement factors were calculated to be 10~6 as compared with solution spectra. The technique was applied to investigate the self-assembly of benzyl disulfide and adsorption orientation of thiophenol on silver surfaces. The results show that the HNO_3 roughened silver foil seems to be a more routinely preparable substrate system for SERS study.
A simple chemical method for preparing SERS active surfaces was developed by etching silver foils in concentrated HNO_3 solutions. The enhancement factors were calculated to be 10~6 as compared with solution spectra. The technique was applied to investigate the self-assembly of benzyl disulfide and adsorption orientation of thiophenol on silver surfaces. The results show that the HNO_3 roughened silver foil seems to be a more routinely preparable substrate system for SERS study.
1991, 7(06): 712-715
doi: 10.3866/PKU.WHXB19910615
Abstract:
Decomposition of formic acid adsorbed on ZrO_2 catalyst was studied by means of TPD and IR spectroscopy. Two peaks of H_2O were observed at about 423 and 623 K in the TPD process. Between the two peaks of H_2O, evolution of CO appeared and gave a peak at about 563 K. IR study showed that the adsorption of formic acid led to the formation of a formate(Ⅰ)and a dimer species(Ⅱ)of the acid on the surface. At 373-473 K, Ⅱ was decomposed to H_2O which produced the first H_2O peak and some new surface formate species (I). At temperature higher than 473 K, the formated species (I), either formed in the initial adsorption of formic acid or produced from II, were decomposed further to CO and surface hydroxyl groups. The main part of the surface hydroxyl groups were eliminated at above 573 K, which produced the second H_2O peak.
Decomposition of formic acid adsorbed on ZrO_2 catalyst was studied by means of TPD and IR spectroscopy. Two peaks of H_2O were observed at about 423 and 623 K in the TPD process. Between the two peaks of H_2O, evolution of CO appeared and gave a peak at about 563 K. IR study showed that the adsorption of formic acid led to the formation of a formate(Ⅰ)and a dimer species(Ⅱ)of the acid on the surface. At 373-473 K, Ⅱ was decomposed to H_2O which produced the first H_2O peak and some new surface formate species (I). At temperature higher than 473 K, the formated species (I), either formed in the initial adsorption of formic acid or produced from II, were decomposed further to CO and surface hydroxyl groups. The main part of the surface hydroxyl groups were eliminated at above 573 K, which produced the second H_2O peak.
1991, 7(06): 716-720
doi: 10.3866/PKU.WHXB19910616
Abstract:
EMF measurement of cell (A) and cell (B)
Pt, H_2(g,101.325 kPa) |HCl(m_1),20 mass% Glucose,
80 mass% H_2O|AgCl-Ag (A)
and
Pt, H_2(g,101.325 kPa)|HGCl(m_1),G(m_2), 20 mass%
Glucose, 80 mass% H_2O|AgCl-Ag (B)
at 5 temperatures ranging from 278.15 to 318.15 K were used to derive (a) the standard emf of the cell with 20 msas% glucose-water. (b) the dissociation constant of glycine by two methods, that is, tradition Debye-Hückel extrapolation and polynomial approximation proposed by us in our former paper. The results obtained from both methods are in od agreement within experiment error.
EMF measurement of cell (A) and cell (B)
Pt, H_2(g,101.325 kPa) |HCl(m_1),20 mass% Glucose,
80 mass% H_2O|AgCl-Ag (A)
and
Pt, H_2(g,101.325 kPa)|HGCl(m_1),G(m_2), 20 mass%
Glucose, 80 mass% H_2O|AgCl-Ag (B)
at 5 temperatures ranging from 278.15 to 318.15 K were used to derive (a) the standard emf of the cell with 20 msas% glucose-water. (b) the dissociation constant of glycine by two methods, that is, tradition Debye-Hückel extrapolation and polynomial approximation proposed by us in our former paper. The results obtained from both methods are in od agreement within experiment error.
1991, 7(06): 721-724
doi: 10.3866/PKU.WHXB19910617
Abstract:
Two peaks, appeared respectively at Ca. 900 K and 800 K on the NH_3-TPD curve of Ni-containing Y zeolite, have been investigated. These two peaks can't be simply explained by means of acidity.
One peak observed at Ca. 90O K, has been contributed to the water gas resulted from the dehydroxylation of zeolite. Another peak, appeared at Ca. 800 K, has been proved to be due to NH_3, formed by decomposation of a complex with the suggested formula Ni~(2+)(NH)_x(OH~-)_(6-x). This complex resulted from the interaction of adsorbed NH_3, the supported Ni~(2+) species and the skeleton OH groups under suitable conditions and decomposed at Ca. 800 K by a first order reaction with an activation energy of about 90.74 kJ·mol~(-1).
Two peaks, appeared respectively at Ca. 900 K and 800 K on the NH_3-TPD curve of Ni-containing Y zeolite, have been investigated. These two peaks can't be simply explained by means of acidity.
One peak observed at Ca. 90O K, has been contributed to the water gas resulted from the dehydroxylation of zeolite. Another peak, appeared at Ca. 800 K, has been proved to be due to NH_3, formed by decomposation of a complex with the suggested formula Ni~(2+)(NH)_x(OH~-)_(6-x). This complex resulted from the interaction of adsorbed NH_3, the supported Ni~(2+) species and the skeleton OH groups under suitable conditions and decomposed at Ca. 800 K by a first order reaction with an activation energy of about 90.74 kJ·mol~(-1).
1991, 7(06): 725-729
doi: 10.3866/PKU.WHXB19910618
Abstract:
The UV and FL spectra of the title compounds were reported and substituent effects of them were discussed in this work. Fairly od correlations between λ_(max)~(uv) and Δσ(σ_p-σ_m), λ_(max)~(FL) and σ_p~+(or σ_m~+), stokes shift values and Δσ were established respectively.It showed that the electron effects of the substituents played a main role Spectra sensitivity toward N(CH_3)_2 and OH substituted compounds were also studied.
The UV and FL spectra of the title compounds were reported and substituent effects of them were discussed in this work. Fairly od correlations between λ_(max)~(uv) and Δσ(σ_p-σ_m), λ_(max)~(FL) and σ_p~+(or σ_m~+), stokes shift values and Δσ were established respectively.It showed that the electron effects of the substituents played a main role Spectra sensitivity toward N(CH_3)_2 and OH substituted compounds were also studied.
1991, 7(06): 730-734
doi: 10.3866/PKU.WHXB19910619
Abstract:
A new method for determination of reaction order n by DTG curve is presented in this paper. The reliability of the method is illustrated by the investigation of the decomposition process of CaC_2O_4·H_2O.
The result shows that the peak area of DTG Curve corresponds to the change of sample weight. The reaction order n may be determined by the following equation:
1-x_m=1/e (n=1); 1-x_m=n~(1/(1-n)) (n≠1)
Where x_m represents the fraction reacted at maximum rate of the reaction, x_m can be calculated by the ratio of sample changed at the top of DTG peak ...
A new method for determination of reaction order n by DTG curve is presented in this paper. The reliability of the method is illustrated by the investigation of the decomposition process of CaC_2O_4·H_2O.
The result shows that the peak area of DTG Curve corresponds to the change of sample weight. The reaction order n may be determined by the following equation:
1-x_m=1/e (n=1); 1-x_m=n~(1/(1-n)) (n≠1)
Where x_m represents the fraction reacted at maximum rate of the reaction, x_m can be calculated by the ratio of sample changed at the top of DTG peak ...
1991, 7(06): 735-739
doi: 10.3866/PKU.WHXB19910620
Abstract:
The anodic and cathodic processes of pyrite in acid solution of sulfate and chloride have been studied.
The stable products of anodic processes are Fe~(3+), SO_4~(2-), as well as Fe~(2+) and S. The first stage of anodic reaction is:
FeS_3= Fe~(2+)+2S+2e~- (1)
followed by the oxidation of Fe~(2+) to Fe~(3+) and the production of SO_4~(2-). The relationship of overpotential (η) and the current density (Ⅰ) can be represented by the equation:
η=0.26+0.115lgI
the exchange current density is 0.005 A·m~(-2), and the standard rate constant is 2.58×10~(-8) ms~(-1).
The mechanism for the reaction (1) might be expressed as:...
The anodic and cathodic processes of pyrite in acid solution of sulfate and chloride have been studied.
The stable products of anodic processes are Fe~(3+), SO_4~(2-), as well as Fe~(2+) and S. The first stage of anodic reaction is:
FeS_3= Fe~(2+)+2S+2e~- (1)
followed by the oxidation of Fe~(2+) to Fe~(3+) and the production of SO_4~(2-). The relationship of overpotential (η) and the current density (Ⅰ) can be represented by the equation:
η=0.26+0.115lgI
the exchange current density is 0.005 A·m~(-2), and the standard rate constant is 2.58×10~(-8) ms~(-1).
The mechanism for the reaction (1) might be expressed as:...
1991, 7(06): 740-746
doi: 10.3866/PKU.WHXB19910621
Abstract:
