Showing papers by "Xiamen University published in 1997"
TL;DR: In this paper, the NiO and MgO components in this catalyst precursor formed, due to their highly mutual solubility, a NixMg1 − xO solid solution, and the high dispersion of Ni-species in this solid solution and the effect of valence-stabilization by the mgO crystal field would be in favor of inhibiting deep reduction of Ni2+ to Ni0 and aggregation of the Ni0 to form large metal particles at the surface of catalyst.
337 citations
TL;DR: In this article, supported Au catalysts were obtained by attaching Au phosphine complexes on as-precipitated metal hydroxides, followed by temperature-programmed calcination in a flow of dry air.
172 citations
TL;DR: In this article, confocal microprobe Raman spectroscopy and a unique electrochemical pretreatment procedure for the Pt surface were used to extend the detailed surface Raman studies, for the first time, to bare Pt electrodes in a wide potential region (e.g. −1.0 to +1.4 V vs SCE) and to more general adsorbates such as SCN and CO having small Raman scattering cross sections.
Abstract: By using confocal microprobe Raman spectroscopy and a unique electrochemical pretreatment procedure for the Pt surface, we are able to extend the detailed surface Raman studies, for the first time, to bare Pt electrodes in a wide potential region (e.g. −1.0 to +1.4 V vs SCE) and to more general adsorbates such as SCN- and CO having small Raman scattering cross sections. Taking advantage of being capable of observing the adsorbate−metal vibrational bands in the low-frequency region over IR and SFG techniques, the surface Raman spectroscopy has demonstrated the virtues of yielding detailed information on the surface bonding affected by surface coverage, coadsorbate, electrolyte ions, and electrode potential. The potential-dependent Raman spectra of SCN- reveal that the N-bound adsorbate is favored at the more negative potentials. The orientation conversion to the S-bound species occurs in the more positive region, depending on the SCN- concentration. In a solution of 10-5 M NaSCN and 0.1 M NaClO4, a new C−N...
144 citations
TL;DR: In this article, a theoretical comparative study of methane dissociation on Ni, Pd, Pt and Cu surfaces has been carried out using a quasirelativistic density functional method.
77 citations
TL;DR: In this paper, surface enhanced Raman scattering from pyrazine adsorbed on roughened Ni electrodes was observed for the first time, and a special surface roughening procedure was carried out by a HNO3-etching method to obtain high-quality surface spectra.
73 citations
TL;DR: In this article, the electronic structure, geometries and magnetic moment of small Co n (n = 2−8) clusters have been studied by using nonlocal density functional calculations, and the calculated bond dissociation energies in most cases are in good agreement with the collision-induced dissociation experiment.
72 citations
TL;DR: In this paper, the role of the surface oxides of a polycrystalline surface of a Pt polysilicon surface in the electrocatalytic oxidation of C1 to C4 primary alcohols has been investigated.
70 citations
TL;DR: Rivanol binds to the double helical DNA with a high affinity, as deduced from the absorption and fluorescence spectral data and the results of competitive binding studies proved the intercalation of RVN into DNA base stack.
68 citations
TL;DR: It is suggested that Cu(+) ions locate in the open channels of the ZSM-5 framework and bind to mixed (Si- and Al-) bridged oxide ion and exist as a CuO cluster in small cages as well as in open channels.
Abstract: Cu−ZSM-5 samples with various Cu+/Cu2+ ratios have been successfully prepared in three different methods and studied by XPS and FTIR. Cu+ ions are found, by XPS, to mainly exist in the samples prepared by solution ion exchange and microwave solid-state reaction exchange. On the basis of the chemical shift of the Al 2p core level to a higher binding energy [Al(species II)], with the atomic ratio of Cu+/Al(species II) being approximately one, and the vanishing of the IR band at 3640 cm-1 due to copper exchange, it is suggested that Cu+ ions locate in the open channels of the ZSM-5 framework and bind to mixed (Si- and Al-) bridged oxide ion. From the ZSM-5 pore structure consideration, as well as from the observed decrease in the IR intensity ratio of bands 550/450 cm-1 with enhanced Cu2+ loading, it is also suggested that Cu2+ ions are a predominant Cu species in solid-state reaction exchanged Cu−ZSM-5 samples and exist as a CuO cluster in small cages as well as in open channels. The IR bands at 907 and 964...
63 citations
TL;DR: In this article, TPR and EPR techniques have been employed to characterize the catalytic performances of high-purity rare-earth orthovanadates, and in situ Raman experiments confirmed the presence of low-valence vanadates at the catalyst surface in the reaction process.
Abstract: High-purity rare-earth orthovanadates
(R
E
VO
4
), PrVO
4
, GdVO
4
,
DyVO
4
, HoVO
4
, ErVO
4
,
NdVO
4
, TbVO
4
and LuVO
4
, have been
prepared by the citrate method. XRD, FTIR, LRS, UV–VIS diffuse
reflectance, TPR and EPR techniques have been employed to characterize
them. The catalytic performances of PrVO
4
,
ErVO
4
, GdVO
4
, DyVO
4
and
NdVO
4
in the oxidative dehydrogenation of propane can
compete with that of Mg
3
V
2
O
8
. The
selectivity of propene over TbVO
4
, LuVO
4
and
HoVO
4
was relatively low. TPR results showed that the more
easily the catalyst is reduced, the higher the propene selectivity.
EPR and in situ Raman experiments confirmed the
presence of low-valence vanadates at the catalyst surface in the
reaction process. We observed that 18
O
2
-isotope
exchange occurred over the catalysts via a double-step single
exchange process and the activity of the catalysts increased with an
increase of isotope exchange rate.
58 citations
TL;DR: In this paper, the activation of molecular oxygen on the surface of cerium oxide and the reactivities of surface oxygen species with methane and ethane were studied by means ofin situconfocal microprobe Raman spectroscopy in the temperature range 298-1023 K.
Abstract: The activation of molecular oxygen on the surface of cerium oxide and the reactivities of surface oxygen species with methane and ethane were studied by means ofin situconfocal microprobe Raman spectroscopy in the temperature range 298–1023 K. The results showed that O22-, O2- and O2δ- (0<δ<1) adspecies formed on the surface of an oxygen-pretreated cerium oxide sample when the temperature was below 423 K. As the temperature was increased, some oxygen species desorbed from the sample surface. At 1023 K, only the CeO2F2gpeak (at 449 cm-1) and O2- species (at 1159 cm-1) were observed on the CeO2 surface. In the absence of gaseous oxygen, ethane reacted with lattice oxygen species and diatomic oxygen adspecies, including O22-, O2- and O2δ- (0<δ<1) below 373 K. In contrast, the reactions of methane with superoxide and lattice oxygen species apparently did not take place until the temperature was increased to 1023 K. © 1997 by John Wiley & Sons, Ltd.
TL;DR: The adsorption of CO on dispersed thin layers of platinum and palladium supported on glassy carbon (Pt/GC and Pd/GC) was studied using in sity multi-step FTIR spectroscopy (MS-FTIRS) as discussed by the authors.
TL;DR: In this article, a method for the determination of nucleic acids with methylene blue (MB) as a fluorescence probe was developed, based on the quenching of the fluorescence of MB in the presence of NAs.
Abstract: A method for the determination of nucleic acids with methylene blue(MB) as a fluorescence probe was developed, based on the quenching of the fluorescence of MB in the presence of nucleic acids. The calibration graph was linear in the range of 0–40 μg/ml for CT DNA and 0–55 μg/ml for yeast RNA, the limit of detection was 28 ng/ml for CT DNA and 82 ng/ml for yeast RNA. CT DNA could be determined in the presence of 30%(w/w) yeast RNA and yeast RNA was determined when the content of CT DNA in synthetic samples was below 5%(w/w).
TL;DR: In this article, the mechanism of glucose oxidation on a Pt|WO3 electrode in sulphuric acid medium was investigated by HPLC and in-situ FTIR spectroscopy, the major oxidation products were identified to be glucono-δ-lactone, CO2 and a probable five-member ring lactone.
TL;DR: In this article, the authors present a careful study of the energy of substitution in aluminum in both the bulk and small cluster environments, based on the pseudopotential method with plane-wave expansion and periodic boundary conditions.
Abstract: We present a careful study of the energetics of vacancy and substitutional impurities in aluminum in both the bulk and small cluster environments. The calculations are done within the framework of the local-density-functional formalism and are based on the pseudopotential method with plane-wave expansion and periodic boundary conditions. Both the ionic and electronic degrees of freedom are fully relaxed. The electronic structure problem is treated with a preconditioned conjugate-gradient method that applies equally well to insulators and metals, and is suitable for parallel computing. We have considered up to 216 atoms in the supercell, and we show that reliable results can be obtained with 108-atom cells with proper {bold k}-point sampling. Vacancy-formation energy, heats of solution of the impurities and the relaxations near the defects are in good agreement with available experimental data. The energetics of substitution in small clusters was found to be rather different from bulk. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: The preferential uptake of selenite (Se(IV) over selenate (VI) by the marine phytoplankters Chaetoceros calcitrans and Chlorella vulgaris was demonstrated in this article.
02 Jun 1997
TL;DR: In this article, the impingement cooling midchord region of the gas turbine aerofoils in case of an initial crossflow is also present, where the relative position of the jet hole to the ribs is investigated.
Abstract: Impingement heat transfer from rib roughened surface within two-dimensional arrays of circular jet has been investigated experimentally After the jet impinges on the rib roughened surface parallel to the jet plate, it is constrained to exit in a single direction along the channel formed by the jet plate and the rib roughened surface An initial crossflow is present which approaches the arrays through an upstream extension of the channel The configurations considered are intended to simulate the impingement cooling midchord region of the gas turbine aerofoils in case where an initial crossflow is also present The study covered four different relative positions of the jet hole to the ribs: jet hole before the rib (−p/4), jet hole on the rib, jet hole behind the rib (+p/4) and jet hole between the ribs (midst,+p/2) The tests were performed for Reynolds number Re = 8000 and 15000, and the nondimensional jet-to-surface spacing z/d = 14, 20 and 30 The test results show that the impingement heat transfer from the rib roughened surface can be considerably improved by adequately arranging the relative position of the jet hole to the ribsCopyright © 1997 by ASME
TL;DR: In this article, the authors investigated the distribution and characterization of remaining mangrove stands in Hong Kong and found that 43 mangroves still remained along the coastline of Hong Kong despite tremendous reclamation and development which occurred in the past 40 years.
Abstract: Ecological surveys were carried out to investigate the distribution and characterization of remaining mangrove stands in Hong Kong The field studies indicate that 43 mangrove stands, excluding Mai Po Nature Reserve, still remained along the coastline of Hong Kong despite tremendous reclamation and development which occurred in the past 40 years Most mangrove stands were found in Deep Bay (western part) and Sai Kung District (eastern coasts) The total areas occupied by these mangrove stands were 178 ha, varying from a very small stand (with 1–2 mangrove shrubs) to fairly extensive mangroves in Deep Bay (> 10 ha) It appeared that mangrove stands located in Deep Bay area were larger than those in the eastern coasts Twenty plant species were identified from these stands, with 13 being exclusive or associate mangrove species The major constituent species were Kandelia candel, Aegiceras corniculatum, Excoecaria agallocha and Avicennia marina Rare species such as Heritiera littoralis were only found in a few mangrove stands Out of the 43 remaining mangrove stands, 23 were more worthwhile for conservation and their plant community structures were further investigated by transect and quadrat analyses The importance values (sum of relative abundance, frequency and dominance) show that K candel was the most dominant species Species richness and Simpson’s indices together with tree height, tree density and canopy area fluctuated significantly between mangrove stands These values were used to prioritize the conservation potential of the remaining mangrove stands in Hong Kong
TL;DR: In this article, the anion of the complex contains a bent (MoO 2 )O(MoO2 ) core with an MoOMo angle 142°.
TL;DR: In this article, the performance of a thermoelectric device used as a heat pump or refrigerator is mainly affected by the Peltier, Fourier, Joule and Thomson effects.
TL;DR: In this article, the surface Raman spectra of pyridine adsorbed at Ru, Rh and Pd film electrodes deposited on glassy carbon (GC) substrates respectively have been obtained, for the first time, by utilizing a highly sensitive confocal Raman microscope.
TL;DR: In this article, the authors show that scalar driving with positive conditional Lyapunov exponents can achieve synchronization of spatio-temporal chaos in a driven subsystem with a first-order dissipative effect.
Abstract: Computer simulations show that, following the scalar driving approach, synchronization of spatiotemporal chaos can also be achieved in driven subsystem with positive conditional Lyapunov exponents. This is a result of the so-called extreme trap. In the neighborhood of the maximum value, the higher-order term of difference causes a first-order dissipative effect, which is not reflected by the conditional Lyapunov exponents. Hence the actual average divergence rate is smaller than the maximum conditional Lyapunov number and thus causes the driven system to synchronize even when the conditional Lyapunov exponents are positive.
TL;DR: A novel fluorimetric method has been developed for rapid determination of DNA and RNA with hypocrellin A (HA) as a fluorescence probe, based on the fluorescence enhancement of HA in the presence of DNA or RNA.
Abstract: A novel fluorimetric method has been developed for rapid determination
of DNA and RNA with hypocrellin A (HA) as a fluorescence probe, based on
the fluorescence enhancement of HA in the presence of DNA or RNA. Maximum
fluorescence is produced in the pH range 3.4–4.0, with maximum
excitation and emission wavelengths at 470 and 600 nm, respectively. Under
optimal conditions, the calibration graphs are linear over the range
0–200.0 ng cm
-
3
for calf thymus DNA and
13.0–200.0 ng cm
-
3
for yeast RNA,
respectively. The corresponding detection limits are 5.0 ng
cm
-
3
for calf thymus DNA and 13.0 ng
cm
-
3
for yeast RNA. The relative standard
deviation of six replicate measurements is 4.5% for 100 ng
cm
-
3
calf thymus DNA. DNA could be determined
in the presence of 20% m/m yeast RNA. The mechanism for the binding of HA
to DNA is also studied.
TL;DR: In this paper, a polyaniline (PANI) film formed under the effects of the magnetic field was characterized in situ conductivity measurements with four microprobe electrodes were performed in acid aqueous solution.
TL;DR: Li et al. as discussed by the authors discovered a new kind of current oscillation during the reduction or oxidation of some anions, which appeared over the limiting reduction and oxidation current of the anions and was loaded on the current of hydrogen or oxygen evolution.
TL;DR: In this article, a triclinic ammonium dicitratonickelate (II) dihydrate (NH4)4[Ni(Hcit)2] ·2H2O, 2, (H4cit = citric acid) has been synthesized and characterized by spectroscopic methods.
Abstract: Dimeric ammonium diaquocitratonickelate (II) dihydrate (NH4)2[Ni(Hcit)(H,O)2]2 -2H2O, 1, and its sodium and potassium salts, as well as ammonium dicitratonickelate (II) dihydrate (NH4)4[Ni(Hcit)2] ·2H2O, 2, (H4cit = citric acid) have been synthesized and characterized by spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray methods. Compound 1 is triclinic. space group Pl with a = 6.4071(7), b = 9.4710(7), c = 9.6904(5) A, α = 105.064(5), β = 91.992(7). γ = 89.334(8)°, V = 567.5(1) A Z = 1, R = 0.037 for 1714 observed reflections. The structure consists of centrosymmetric dimers, [Ni(Hcit)(H2O)2]2 2- The principal Ni[sbnd]O dimensions are Ni[sbnd]O(hydroxy), 2.074(2)A, Ni[sbnd]O(α-carboxy), 2.020(3)A, Ni[sbnd]O(β-carboxy), 2.031(2). 2.037(2)A, Ni[sbnd]O(water), 2.065(2), 2.072(3)A. Compound 2 crystallizes in the monocliruc space group P 21/a with a = 9.361(1), b= 13.496(1), c = 9.4238(7)A, (3= 115.475(6)°, V= 1074.9(3)A;. Z= 2, R = 0.052 for 1507 observed reflections. ...
TL;DR: The cathodic disbonding of a thick, pigmented polyurethane coating from steel in 3.5 wt.% NaCl solution was studied by using an electrochemical AC impedance technique as mentioned in this paper.
TL;DR: In this article, the electrooxidation of 1-butanol (1-BL) on Pt electrodes was studied using cyclic voltammetry and in situ FTIR spectroscopy.
TL;DR: The first asymmetric synthesis of (2R, 3R)-3-amino-1-benzyl-2-methylpyrrolidine, the parent diamine of antipsychotic agent emonapride, from (S)-malic acid was achieved via a highly diastereoselective reductive alkylation as mentioned in this paper.
TL;DR: In this paper, a high speed collision coprecipitation method was used for methanol synthesis and the results indicated that Mn is favorable for the dispersion of copper in the catalysts, preventing the copper particles from sintering.
Abstract: Cu—Zn—Al and Cu—Zn—Al—Mn catalysts, used for methanol synthesis, are prepared by a high speed collision coprecipitation method. The methanol yields are 28.4 and 33.8 mol/l.cat.h over the ternary and quaternary catalysts, respectively. TPR, H 2 -TPD, SEM and FT-IR techniques are used in the study of the catalysts. The results indicated that Mn is favorable for the dispersion of copper in the catalysts, preventing the copper particles from sintering. The diffuse reflectance FT-IR spectra suggested that the formate might be the intermediate in the methanol synthesis.