共查询到20条相似文献,搜索用时 109 毫秒
1.
M. D. Smolikov K. V. Kazantsev E. V. Zatolokina D. I. Kir’yanov E. A. Paukshtis A. S. Belyi 《Kinetics and Catalysis》2010,51(4):584-594
The state of surface Pt atoms in the Pt/SO4/ZrO2/Al2O3 catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al2O3 alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO4/ZrO2/Al2O3 superacid catalyst were used in this study. With the use of IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced
form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties
of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic
activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation
of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization. 相似文献
2.
L. Li X. Wang J. Shen L. Zhou T. Zhang 《Journal of Thermal Analysis and Calorimetry》2005,82(1):103-107
Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO2catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum
catalysts. In addition, microcalorimetric adsorption of H2, O2, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst.
It is found from the microcalorimetric results of H2and O2adsorption that the addition of Ag to Pt/SiO2leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO2catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO
adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO2. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation
of dissociative species (ethylidyne) upon the chemisorption of C2H4on Pt-Ag/SiO2. The differential heat vs. uptake plots for C2H4adsorption on the oxygen-preadsorbed Pt/SiO2and Pt-Ag/SiO2catalysts suggest that the incorporation of Ag to Pt/SiO2could decrease the ability for the oxidation of C2H4. 相似文献
3.
Kinetics of processes occurring at H+/solid electrolyte/Pt, H2 three-phase interface are studied subject to the platinum content on the electrode. The study was performed with model electrochemical
cells PbO2/H3PW12O40/Pt with different platinum content at the working electrode that consisted of platinum deposited onto the E-Tek LT1200-N
carbon-nanotubes paper. On the basis of the obtained results, the occurring processes were practically fully separated. It
is shown by the analyzing of relaxation curves that there exist at least two processes in the system: the faster one corresponds
to the hydrogen reaction; the slower, to the oxygen one. The rates of both processes depend on the platinum content at the
working electrode; they have an extreme at the platinum concentration of 0.5 mg/cm2. Impedance data allowed revealing the processes’ limiting stages. The experimental data allowed suggesting that at low platinum
content the relaxation time is determined by the electrochemical reaction rate; at higher content, by gas diffusion through
the platinum dense layer. 相似文献
4.
2CaO·3B2O3·H2O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and
TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B2O3·H2O in HCl·54.572H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HCl·54.501H2O and of CaO in (HCl+H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol−1 of 2CaO·3B2O3·H2O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method. 相似文献
5.
Majid M. Heravi Khadijeh Bakhtiari Tina Benmorad Fatemeh F. Bamoharram Hossein A. Oskooie Maryam H. Tehrani 《Monatshefte für Chemie / Chemical Monthly》2007,138(5):449-452
Summary. The nitration of aromatic compounds was carried out in the presence of divanadium-substituted molybdophosphoric acid, H5PMo10V2O40, as catalyst and a mixture of nitric acid and acetic anhydride as nitrating agent. In the presence of this heteropolyacid
the ortho- and para-nitro compounds were obtained in good to excellent yields under mild reaction conditions. 相似文献
6.
Ji-min Yang Yan Yao Run-zhi Zhang Ai-de Sun Bao-hui Li Hong-zhi Lu Qi-ying Xia 《Journal of solution chemistry》2009,38(4):429-439
Osmotic coefficients and water activities for the Li2B4O7+LiCl+H2O system have been measured at T=273.15 K by the isopiestic method, using an improved apparatus. Two types of osmotic coefficients, φ
S and φ
E, were determined. φ
S is based on the stoichiometric molalities of the solute Li2B4O7(aq), and φ
E is based on equilibrium molalities from consideration of the equilibrium speciation into H3BO3,B(OH)4− and B3O3(OH)4−. The stoichiometric equilibrium constants K
m
for the aqueous speciation reactions were estimated. Two types of representations of the osmotic coefficients for the Li2B4O7+LiCl+H2O system are presented with ion-interaction models based on Pitzer’s equations with minor modifications: model (I) represents
the φ
S data with six parameters based on considering the ion-interactions between three ionic species of Li+, Cl−, and B4O72−, and model (II) for represents the φ
E data based on considering the equilibrium speciation. The parameters of models (I) and (II) are presented. The standard deviations
for the two models are 0.0152 and 0.0298, respectively. Model (I) was more satisfactory than model (II) for representing the
isopiestic data. 相似文献
7.
V. V. Lesnyak V. K. Yatsimirskii O. Yu. Boldyreva T. D. Kinder 《Theoretical and Experimental Chemistry》2008,44(3):189-194
The catalytic activity in the oxidation of hydrogen (in the gaseous state in the presence of excess oxygen) has been studied
for samples of Pt(Pd)/Ta2O5−x, formed by reduction with hydrogen. The samples obtained had greater activity than the traditional catalysts Pt(Pd)/Al2O3. According to X-ray diffraction analysis and electron microscopic studies, Ta2O5−x becomes amorphous with the formation of more reduced non-stoichiometric oxygen-deficient tantalum oxides with a surface layer
of catalyst.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 180–185, May–June, 2008. 相似文献
8.
The surface area and the pentane isomerization activity of Pt/MoO3 were enlarged by H2 reduction. The enlargements was observed only when the reduction proceeded through the formation of hydrogen molybdenum bronze, HxMoO3. The catalytic activities of H2-reduced MoO3 with different noble metals for pentane isomerization and 2-propanol dehydration depended on the ability of noble metal to produce the HxMoO3 phases. H2-reduced Pt/MoO3 was more active for pentane isomerization than Pt/H, and its activity was comparable to that of Pt/HZSM-5. In heptane isomerization, H2-reduced Pt/MoO3 exhibited a lower activity than Pt/H, although heptane was isomerized very selectively. Strong adsorption of heptane onto H2-reduced Pt/MoO3 is likely to be a reason for its lower heptane isomerization activity. 相似文献
9.
V. V. Lesnyak V. K. Yatsimirskii O. Yu. Boldyreva T. D. Kinder 《Theoretical and Experimental Chemistry》2008,44(4):266-270
X-ray photoelectron spectroscopy (XPS) was used to establish that the surface layer of catalysts obtained by the reduction
of Ta2O5 with added Pt and Pd by hydrogen contains nonstoichiometric oxides TaOx, which enhance the activity of the catalyst. A study of the hydrogen oxidation kinetics showed that the kinetic relationships
are described satisfactorily by the Eley-Riedel mechanism, according to which the reaction occurs by an interaction of hydrogen
from the gas phase with adsorbed oxygen.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 4, pp. 254–258, July–August, 2008. 相似文献
10.
Ag/Al2O3 is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO
x
in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO
x
over a Ag/Al2O3 catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al2O3-reductant systems for the SCR of NO
x
; the low-temperature activity improvement of H2-assisted HC-SCR of NO
x
over Ag/Al2O3; and the application of a Ag/Al2O3-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/Al2O3-reductant systems and H2-assisted HC-SCR of NO
x
over Ag/Al2O3. A SO2-resistant surface structure in situ synthesized on Ag/Al2O3 by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight
into the design of a high-efficiency NO
x
reduction system. The diesel engine bench test results showed that a Ag/Al2O3-ethanol system is promising for catalytic cleaning of NO
x
in diesel exhaust. 相似文献
11.
The absence of experimental evidence for the occurrence of the catalytic reaction 2H2 + O2 → 2H2O on platinum in accordance with the Langmuir-Hinshelwood mechanism was established. It was found that the heterogeneous process can be described more adequately and its nature can be better understood with consideration for chemical transformations involving molecules in a precursor state in a model of the above reaction. The inverse kinetic problem was solved. It was found that the model in which an unambiguously specified set of rate constants for the elementary steps of the reaction was used provided an opportunity to describe experimental data obtained by various authors concerning the oxidation of hydrogen on platinum over the detonating gas pressure range 10?3-105 Pa. The signs of the occurrence of heterogeneous reactions by an adsorption mechanism were found. 相似文献
12.
H. Y. He 《Research on Chemical Intermediates》2011,37(8):1057-1067
Hydrogen gas as a clear energy resource was found to be largely bubbled from a H2O/H2O2/MnWO4 system. MnWO4 powder was fabricated by an aqueous reaction method. The powder was characterized with X-ray diffraction (XRD), transmission
electron microscope (TEM), and X-ray photoelectron spectrometry (XPS). The efficiency of the hydrogen generation increases
with an increase in initial pH in the appropriate range, H2O2 proportion, MnWO4 proportion, and intensity of light resource. Calcining at 400 °C for 1 h can make the MnWO4 powder synthesized by an aqueous reaction more effective for H2 generation and more stable in higher initial pH. The MnWO4 catalyst shows a long-term stability for photocatalytic H2 generation. A mechanism was suggested for the hydrogen generation from the H2O/H2O2/MnWO4 system together with XPS analysis. 相似文献
13.
Xiangzhong Ren Yingkai Jiang Peixin Zhang Jianhong Liu Qianling Zhang 《Journal of Sol-Gel Science and Technology》2009,51(2):133-138
One-dimensional (1D) submicron-belts of V2O5 have been prepared by a sol–gel route using V2O5, H2O2 and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform
infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors
as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement
and cyclic voltammeter. The results showed that the synthesized V2O5 appeared to be submicron-belts and orthorhombic structure. The V2O5 submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge
rate in the potential region 1.8–4.0 V. 相似文献
14.
Fe3O4 nanorods and Fe2O3 nanowires have been synthesized through a simple thermal oxide reaction of Fe with C2H2O4 solution at 200–600°C for 1 h in the air. The morphology and structure of Fe3O4 nanorods and Fe2O3 nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals
Fe3O4 nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air.
When the temperature was 600°C, the samples completely became Fe2O3 nanowires with hexagonal structure. It was found that C2H2O4 molecules had a significant effect on the formation of Fe3O4 nanorods. A possible mechanism was also proposed to account for the growth of these Fe3O4 nanorods.
Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China
(Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010) 相似文献
15.
Jun Wang Wenzhao Li Chunying Yu Yanxin Chen Yingzhen Zhang 《Reaction Kinetics and Catalysis Letters》1997,62(2):217-224
Recucibility of Mo species in Pt/MoO3 and PtMo/Al2O3 has been investigated by temperature-programmed reduction (TPR), temperature-programmed desorption of hydrogen (H2-TPD) and temperature programmed electronic conductivity (TPEC) techniques. In Pt/MoO3 at H2 atmosphere, it was found by TPEC and TPR that, a slight amount of Pt could activate the transfer of the species and H atoms
between H2 and MoO3, and thus accelerate the reduction of MoO3. In PtMo/Al2O3, TPR and H2-TPD revealed that the reduction of surface Mo species could also be facilitated by Pt. Two kinds of hydrogen molybdenum species
were proposed on the surface of the catalyst after prereduction. 相似文献
16.
M. Yu. Smirnov A. V. Kalinkin V. I. Bukhtiyarov 《Journal of Structural Chemistry》2007,48(6):1053-1060
The reactions of the platinum and rhodium model catalysts applied to aluminum oxide with NOx (10 Torr NO + 10 Torr O2) were studied by X-ray photoelectron spectroscopy. The reaction conducted at room temperature formed on the surface of the oxide support the NO 3,s ? nitrate ions characterized by the N1s line at 407.4 eV and O1s line at 533.1 eV and the NO 2,s ? nitrite ions characterized by the N1s line with a binding energy of 404.7 eV. At the same time, the Pt4f and Rh3d lines of the supported platinum particles are shifted toward higher binding energies by 0.5–1.0 eV and 0.7–1.2 eV, respectively. It is assumed that the binding energies increase due to changes in the chemical state of the platinum metal in which oxygen is dissolved. The reaction of NOx with Pt/Al2O3 at 200°C forms platinum oxide defined by the Pt4f 7/2 line with a binding energy of 72.3 eV. 相似文献
17.
Inorganic-organic hybrid membranes containing silica as the structure matrix, poly(N-vinylpyrrolidone) (PVP) as the organic mediating agent and silver ions as olefinic carriers were prepared using sol–gel method and dip-coating process. The structure and permeances of the membranes for N2, He, C2H4, C2H6 at different temperatures indicated that defect-free membranes were obtained and the transportation of the C2H4 through the membranes followed the dissolution and diffusion mechanism. Ideal separation factors of C2H4/C2H6 through the membranes were evaluated at the temperature of 298, 373 and 423 K respectively using mixture gas of 50% C2H4-50% C2H6. The results showed that the ideal separation factors of C2H4/C2H6 through the membranes were obviously greater than the ratio of PC2H4/PC2H6 obtained from the single gas measurement due to the hindering effect by the adsorbed C2H4. The ideal separation factors of C2H4/C2H6 increased with temperature and reached 10 at 423 K, which suggested that C2H4 and C2H6 could be separated at lower humidity compared to the reported organic polymer/silver salt membranes in which humidified gases and higher silver loading were usually used. The transport of C2H4 in the inorganic-organic hybrid membrane was proposed to follow the hopping mechanism, that is, olefins moved across the fixed silver sites. 相似文献
18.
Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V2O5/SiO2 and V2O5/TiO2, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V2O5/SiO2 and V2O5/TiO2 catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V2O5/SiO2 and V2O5/TiO2 were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified. 相似文献
19.
N. I. Giricheva G. V. Girichev N. P. Kuzmina Yu. S. Medvedeva A. Yu. Rogachev 《Journal of Structural Chemistry》2009,50(1):52-59
In the framework of synchronous gas-phase electron diffraction and mass spectrometry experiment, the saturated vapor of N,N′-ethylenebis(salicylaldiminate) copper(II) CuO2N2C16H14 is studied at a temperature T 574(5) K. It is found that evaporation is congruent and the saturated vapor consists of monomeric molecules. Electron diffraction data are proved to correspond to the geometric model for the CuO2N2C16H14 molecule of C 2 symmetry with an almost planar structure of the CuN2O2 coordination fragment and internuclear distances \(r_{h_1 } \)(Cu-O) = 1.917(13) Å and \(r_{h_1 } \)(Cu-N) = 1.931(15) Å. The stuctural parameters obtained are compared to those quantum chemically calculated and molecular parameters in crystals. 相似文献
20.
Catalytic performance of gallia-supported iridium catalysts in the reaction of selective hydrogenation of crotonaldehyde in the gas phase was studied and compared to that of platinum and ruthenium catalysts. The best catalytic properties in terms of the selectivity to crotyl alcohol are shown by 5 wt % Pt/α-Ga2O3 and 5 wt % Ir/α-Ga2O3 catalysts prepared from nonchlorine precursors: Pt(acac)2 and Ir(acac)3, but for the 5 wt % Pt/α-Ga2O3 a very high selectivity of 75% at the high conversion (ca. 60%) is observed. A high selectivity of galia-supported iridium and platinum catalysts was explained by the surface reducibility of gallium oxide leading to covering (decoration) of platinum and iridium by gallium suboxides and the promoting effect of gallium. 相似文献