共查询到20条相似文献,搜索用时 15 毫秒
1.
G. A. El-Shobaky A. S. Ahmad M. Mokhtar 《Journal of Radioanalytical and Nuclear Chemistry》1997,219(1):89-94
A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al2O3 was prepared by impregnating Al(OH)3 with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of -rays (20–160 Mrad). The surface characteristics namelyS
BETVP andr of different treated adsorbents were determined from N2 adsorption isothems measured at –196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O2 at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theS
BET but increased slightly theV
P (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theS
BET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of -rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to -irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites. 相似文献
2.
G. A. El-Shobaky M. M. Doheim A. M. Turky H. A. El-Boohy 《Journal of Radioanalytical and Nuclear Chemistry》2003,256(1):107-113
NiO-doped Co3O4 samples precalcined at 500 °C were subjected to various doses of -rays within the range 0.2-1.6 MGy. The particle size and BET-surface areas of different samples were determined using XRD and nitrogen adsorption at -196 °C. The catalytic reactions studied were conversion of ethanol and isopropanol at 250-400 °C using a micropulse technique and H2O2 decomposition in aqueous solution at 30-50 °C. The results revealed that the -irradiation brought a significant decrease in the particle size of Co3O4 phase with subsequent increase in the SBET surface areas. The treatment brought also a progressive decrease in the total conversion of both alcohol (dehydration and dehydrogenation) falling to a minimum value (about 20% of its initial activity) at a dose of 0.8 MGy. The catalysts retain their initial activity upon exposure to a dose of 1.6 MGy. On the other hand, the catalytic activity in H2O2 decomposition of the investigated system decreased progressively by increasing the dose of -rays and the catalysts lost more than 90% of their initial activity upon exposure to a dose of 1.6 MGy. 相似文献
3.
Nabil H. Amin Gamil A. El-Shobaky Gehan A. Fagal 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(2):211-218
Methanol conversion reaction was carried out in contact with a poorly crystalline -alumina pre-irradiated with different doses of -rays. The reaction was conducted at 140–440°C using a flow technique under atmospheric pressure. The results obtained revealed that -irradiation of Al2O3 resulted in drastic modifications of its activity and selectivity in methanol conversion reaction. The dose of 15 Mrad was sufficient to suppress completely the formation of dimethyl ether (DME) and stimulated the formation of methane, which started at 200°C instead of 300°C in the case of the unirradiated alumina specimen. However, the rate of CH4 formation was found to decrease as a function of the dose employed. When the dose reached 140 Mrad, DME was reproduced with a rate comparable to that measured for the unirradiated catalyst sample. These results permitted us to conclude that DME is produced on the weak acidic sites (Brönsted acidity of Al2O3) and is not necessarily an intermediate compound for methane formation that takes place directly from methanol on strong acidic sites (Lewis acidity). The doses of 15–75 Mrad expelled completely the Brönsted acidic sites from Al2O3 surface, and the doses above this limit brought about a transformation of Lewis acidic sites into Brönsted acidity that is responsible for dimethyl ether formation. This transformation occurs by the action of liberated water from the dehydration of methyl alcohol. 相似文献
4.
Tsykoza L. T. Ismagilov Z. R. Ushakov V. A. Kuznetsov V. V. Ovsyannikova I. A. 《Kinetics and Catalysis》2003,44(6):806-812
The phase composition of supported Mn–Al–O catalysts and their activity in the reaction of methane oxidation were studied depending on the composition of aluminum oxide supports (-Al2O3 with different -Al2O3 contents modified with individual Mg, La, and Ce oxides or Mg + La and Mg + Ce oxide mixtures) and calcination temperatures (500, 900, and 1300°C). It was found that the Mn–Al–O catalysts based on -alumina containing -Al2O3 and modified with Mg, La, or Ce additives are more active and thermally stable (up to 1300°C) than the samples based on pure -Al2O3. A conclusion was drawn that a higher degree of disorder of the structure of -Al2O3, compared to that of -Al2O3, is favorable for a deeper interaction of manganese and modifying additives with the support at the early stages of the synthesis and for the formation of Mn–Al compounds with complex composition (solid solutions and/or hexaaluminates) at 1300°C. These compounds are responsible for the stability and high activity of the catalysts in methane oxidation. 相似文献
5.
G. A. El-Shobaky N. H. Amin G. A. Fagal 《Journal of Radioanalytical and Nuclear Chemistry》1994,178(1):3-9
The catalytic conversion of isopropanol was conducted over a poorly crystalline -alumina irradiated with different doses of -rays (25–150 Mrad). The catalytic reaction was carried out at 180–400°C in a flow technique under atmospheric pressure. The results showed that the dose of 25 Mrad resulted in a decrease of about 50% of the dehydration activity which suffered a further slight decrease upon irradiation at a dose of 50 Mrad. Increasing the dose in the range of 50–150 Mrad effected an increase in the dehydration activity reaching a maximum limit at 100 Mrad, then decreased abruptly by a dose of 150 Mrad. -irradiation led also to creation of some active sites contributing in dehydrogenation of isopropanol to producing acetone. These results were discussed in terms of removal of Brönsted acidity (25–50 Mrad), responsible for the dehydration reaction and to transformation of Lewis to Brönsted acidity (100 Mrad) by the action of liberated water from the dehydration reaction. The drop in dehydration activity due to irradiation at 150 Mrad might result from an efficient removal of the Brönsted acid sites created. The induced dehydrogenation activity of irradiated aluminas was attributed to creation of some electron-donor centers. 相似文献
6.
Several powder samples of TiO2 are pretreated thermally at 300, 480 and 540°C, subjected to -irradiation and after irradiation added in one of the compartment of the concentration cell made up of Ag/Ag+. The adsorbed oxygen species O
2ad
–
, HO
2ad
–
and O
ad
–
on TiO2 provide negatively charged sites and develop EMF in the cell. The radiation damage, measured in terms of equilibrium EMF, received at lower doses is partially recovered at higher doses. It is proposed that in heating at 480°C, ad species react with Ti3+ ions in the surface and produce –O–O– peroxy linkages and block the negatively charged sites while in heating at 540°C Ti4O7 phase is produced on the surface which adsorbs O2 and provide large number of negatively charged sites. During -irradiation peroxy linkages are broken and the Ti4O7 phase is destroyed. Observed oscillatory variation in equilibrium EMF is explained on the basis of several reactions mentioned above proceeding at different rates during radiolysis. 相似文献
7.
V. N. Doroshenko V. N. Kaurkovskaya E. P. Yakubenko D. I. Pobokin I. R. Entinzon V. M. Ogenko 《High Energy Chemistry》2002,36(3):157-162
The solid-phase decomposition of the iron formate crystal hydrate Fe(HCOO)2 · 2H2O under exposure to 60Co -rays or 3.5-MeV electrons was studied. It was found that the irradiation of this salt to absorbed doses of 0.1–2 MGy resulted in the radiolysis of water of crystallization and the HCOO– anion and in the reduction or oxidation of the Fe2+ cation. The composition of the solid-phase (-Fe, -Fe, FeO, -Fe -Fe2O3, Fe3O4, and FeCO3) and gaseous (H2O, CO, CO2, HCOOH, and CH4) radiolysis products of the substance was determined. 相似文献
8.
S. A. H. Ali N. A. Hassan A. I. Kira 《Journal of Radioanalytical and Nuclear Chemistry》1994,187(3):223-236
Four different samples of NdX, NdY, NdNH4X and NdNH4Y-zeolites were prepared by ionexchange methods. DTA and XRD analyses have been carried out for the samples. The thermally activated zeolites were irradiated by 1.5 and 10.0 Mrad -rays. The catalytic activities of these samples were tested in dehydration of isopropanol. The results of DTA indicated that all samples showed endothermic peaks at about 215 °C related to the release of physically adsorbed water and exothermic peaks at 850–950 °C indicating the collapses of the zeolite. The X-ray analysis revealed that the exchange of sodium by neodymium or ammonium followed by neodymium ions did not change the crystal structure but some decrease in the crystallinity was observed. The catalytic activities of these zeolites were measured in dehydration of isopropanol as a function of temperature. It was found that the activity of the prepared Nd-zeolites depends on the crystallinity of zeolites and on the condensation products formed on catalyst surface. However, the irradiated samples exhibited higher catalytic activities in isopropanol conversion than the unirradiated ones. The observed higher activity for irradiated samples was attributed to the increase of the number of acidic centers responsible for dehydration of alcohols. These centers were formed as a result of the formation of tricoordinate aluminium atoms in -irradiated zeolites. 相似文献
9.
The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, S
D, vary from 49.07 mJ·m–2 at 25°C to 17.20 mJ·m–2 at 150°C. The S
D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of S
D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the S
D values as well as in the dispersive component of the surface enthalpy, h
S
D. Such abrupt change can be attributed to an entropic contribution of the surface free energy. 相似文献
10.
Transparent and porous boehmite, -Al2O3 (500°C) and -Al2O3 (900° and 1000°C) thin sheets (50–100 m) have been prepared from boehmite sols. -Al2O3 shows about 48% porosity and 292 m2/g surface area. On transformation from -Al2O3 (500°C) to -Al2O3 (900°C), the porosity still remains high, i.e. 45%; however, the surface area becomes 138 m2/g. The porosity and surface area of -Al2O3 become about 41% and 97 m2/g respectively on further heating to 1000°C. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both -Al2O3 and -Al2O3 show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the - and -Al2O3. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium. 相似文献
11.
Lamellar single crystals of some regio-selectively substituted cellulose hetero-esters: cellulose propionate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propionyl cellulose), cellulose acetate dipropionate (CADP, 6-O-acetyl-2,3-di-O-propionyl cellulose), cellulose butyrate diacetate (CBDA, 2,3-di-O-acetyl-6-O-butyryl cellulose) and cellulose acetate dibutyrate (CADB, 6-O-acetyl-2,3-di-O-butyryl cellulose), have been prepared at high temperature in a mixture of dibenzyl ether andn-tetradecane. The CPDA crystals were lozenge-shaped whereas those of CADP, CBDA and CADB had a ribbon morphology. CPDA crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a*=0.807 nm–1,b
*=0.400 nm–1 and
*=90° could be determined. Systematic absences occurred at every odd reflection along the two orthogonal axesa
*andb
*. Thus, the CPDA diffraction pattern is consistent with a pgg symmetry. For CADP, the electron diffraction pattern is consistent with a pmg two-dimensional space group withb the unique axis along the ribbon direction. The diagram yields the reciprocal lattice parameters a* = 0.902 nm–1,b
*=0.651 nm–1 and
*=90°. The CBDA electron diffractogram yields the following cell parameters and two-dimensional space group:a
*=0.482 nm–1,b
*=0.659 nm–1 and
*=90°, and a pgg symmetry; and that of CADB:a
*=0.834 nm–1,b
*=0.645 nm–1 and
*=90°, and a pmg symmetry. 相似文献
12.
V. G. Dedgaonkar D. B. Sarwade S. Mitra 《Journal of Radioanalytical and Nuclear Chemistry》1985,93(5):303-308
Variable temperature /303–553 K/ IR spectroscopic studies are made during thermal decomposition of pure and -treated ammonium perchlorate /AP/. Decomposition is enhanced by radiation or in the presence of an additive /Gd2O3/. Intensity of the stretching /1100 cm–1/ and bending /625 cm–1/ frequencies of ClO
4
–
decrease on heating the KBr matrix even below 360 K. Above this temperature, a broad band develops over 480–510 cm–1 in the pure and -treated AP which is attributed to ClO
3
–
/4/. 相似文献
13.
Moo-Jin Kim Soo-Hyun Chang Jung-Sik Choi Wha-Seung Ahn 《Reaction Kinetics and Catalysis Letters》2004,82(1):27-32
Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al2O3 catalyst exhibited much better catalytic activity than the Rh-Ni/-Al2O3 catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe3O4—Cr2O3) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
14.
The influence of MgO dispersed on -Al2O3 in different amounts on the structure and performances of Pd/-Al2O3 catalysts has been studied by means of XRD, H2–O2 titration, BET and catalytic activity test for CO oxidation. It was found that introduction of MgO enhanced greatly the CO oxidation activity of catalyst. It seems that the enhanced activity stems from the stronger interaction between MgO and -Al2O3 at a given temperature (e.g. 450 °C). 相似文献
15.
Crotyl phenyl sulfide is converted to 2-ethyl-2,3-dihydrobenzothiophene and 2- and 4-methylthiochromans in the presence of -Al2O3 and 5, 10, and 20% ZnCl2/Al2O3 at 300°C and is also isomerized to 1-butenyl- and 3-butenyl phenyl sulfides and cleaved to thiophenol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1337–1339, October, 1973. 相似文献
16.
A. M. Pak O. I. Kartonozhkina G. T. Izdebskaya V. N. Ermolaev A. V. Koroiev 《Russian Chemical Bulletin》1993,42(7):1257-1259
The stereoselective hydrogenation of 2-hexyne in ethanol on Cu/-Al2O3 catalysts (1–40 % Cu) at 4–10 atm and 80–120 °C has been studied. The reaction affordscis-2-hexene as the only reaction product in 100 % yield at [Cu] 30 %. For samples with 20 % Cu, hydrogenation proceeds in parallel with absorption of H2 by the catalyst.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1314–1315, July, 1993. 相似文献
17.
I. I. Mustafaev M. Ya Bakirov K. M. Yakubov Kh. M. Gadzhiev N. K. Gulieva 《Journal of Radioanalytical and Nuclear Chemistry》1985,94(1):1-8
The regularities of H2, CO, and CH4 formation at -radiolysis of brown coals, hard coal, petroleum-bituminous rock, petroleum bitumen, tar, and petroleum residue have been studied at room temperature, absorbed radiation dose 30–2400 kGy, dose intensity 1.6–21.1 kGy/h. The radiation-chemical yields of these gases were found to constitute °Gr0.005–0.07 mol/100 eV for coals, and °Gr0.3–0.6 mol/100 eV for petroleum residues. 相似文献
18.
D. Panayotov 《Reaction Kinetics and Catalysis Letters》1996,58(1):73-78
The activity of –Al2O3-supported CuxMn3-xO4 catalysts towards the reduction of NO with CO has been investigated at temperatures of 150–500°C. It was established that the most active sample is Cu1.01Mn1.99O4/–Al2O3,i.e. the sample where the CuMn2O4 spinel is formed. In the presence of oxygen and the reducing agents CO and HC (a propane-butane mixture) oxygen has no blocking effect on the NO+CO reaction. Under oxidative conditions the reactions NO+CO and O2+CO are competitive. 相似文献
19.
Zuyi Tao Wenming Dong Jingzhou Du Zhijun Guo 《Journal of Radioanalytical and Nuclear Chemistry》1996,214(2):147-157
The effect of different solid components of calcareous soil on the retention of I was investigated by a batch technique and selective extraction method, and the effect of -irradiation was also investigated. The sorption and desorption isotherms of I on the one untreated, three treated soils and the calcareous soil irradiated with -rays were determined at 30 °C, pH 8.1±0.2 and in the presence of 1.0×10–4M or 0.67×10–5M CaCl2. It was found that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale, that iodine can be easily transported in the calcareous soil and that the exceptionally high contribution of organic matter to the iodine sorption is demonstrated. 相似文献
20.
M. A. Ryaskentseva 《Russian Chemical Bulletin》1996,45(8):2015-2017
The 2 % Re/sibunite catalyst is more active than 2 % Re/-Al2O3 and 2 % Re/-Al2O3 catalysts in the dehydrogenation of cyclohexane into benzene (T = 350 °C,w = 0.5 h–1). The substitution of NH4ReO4 by HReO4 in the preparation of the catalyst enhances its activity by a factor of 1.3. Treatment with HNO3 or oxalic acid increases the selectivity by a factor of 1.2 and 1.35, respectively, the overall conversion of cyclohexane being 32–40 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2119–2121, August, 1996. 相似文献