共查询到20条相似文献,搜索用时 15 毫秒
1.
Yun Hau Ng Izan Izwan Hadi Nur Mohd Nazlan Mohd Muhid Halimaton Hamdan 《Journal of fluorine chemistry》2007,128(1):12-16
A series of amphiphilic fluorinated zirconia containing titanium was prepared by titanium impregnation followed by fluorination and alkylsilylation of zirconium oxide. Physical properties of the resulting samples were characterized by XRD analysis, UV-vis spectroscopy, BET surface area analysis and EDAX analysis. The effects of fluorine and alkylsilane groups on the samples were studied by the epoxidation of 1-octene with aqueous hydrogen peroxide. The epoxidation of alkenes is one of the most important methods of functionalizing simple hydrocarbons. The amphiphilic fluorinated catalysts were more active and more efficient than the conventional titania-silica and zirconia-silica mixed oxides in linear alkene epoxidation; enhanced by the presence of alkylsilane and fluorine groups in the catalysts. Modification with alkylsilane successfully induces the hydrophobic behavior of zirconia which is hydrophilic in nature; whereas fluorine was chosen for its electron-withdrawing effect which further activates the titanium active sites. 相似文献
2.
Feixue Gao Toshihiro Yamase Hideo Suzuki 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):97-108
The H2O2-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu4nN]4[Pr2iNH3]2H[P{Ti(O2)}2W10O38]·H2O (1) (with two η2-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. 31P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)}2W10O38]7−or [P{Ti(OOH)}Ti(O2)W10O38]7−. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H2O2] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst. 相似文献
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Intramolecular epoxidation is shown to occur when trimethyl ortho oleate is treated with H2O2. 相似文献
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A series of Au/Fe2O3/Al2O3 catalysts were prepared by the homogeneous deposition-precipitation method. The catalytic activity of the catalyst samples for selective catalytic reduction of NO by propene under oxygen-rich atmosphere was evaluated. The results showed that 2%Au/10%Fe2O3/Al2O3 exhibited good low-temperature activity. The maximum of NO conversion reached 43% at 300 °C, while it was only 21% over the 2%Au/Al2O3 catalyst at the same temperature. The addition of 2% steam to the feed gas had little effect on the catalytic activity. X-ray diffraction results indicated that both Au and Fe2O3 particles were highly dispersed over Al2O3. H2-temperature-programmed reduction results indicated that there was strong interaction between Au and Fe2O3, which made the reduction of Fe2O3 easy. The synergistic effect between Au and Fe2O3 was probably responsible for the good catalytic performance of the Au/Fe2O3/Al2O3 catalyst at low temperature. 相似文献
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In this study, a new facile preparation method of nanocomposites consisting of graphene oxide and manganese dioxide nanowires(GO/MnO_2 NW_s) was developed. The morphology, structure and composition of the resulted products were characterized by transmission electron microscopy, X-ray diffraction and N_2 adsorption and desorption. The GO/MnO_2 nanocomposite was used as an electrode material for non-enzymatic determination of hydrogen peroxide. The proposed sensor exhibits excellent electrocatalytic performance for the determination of hydrogen peroxide in phosphate buffer solution(PBS, pH7) at an applied potential of 0.75 V. The non-enzymatic biosensor for determination of hydrogen peroxide displayed a wide linear range of 4.90 mmol L~(-1)–4.50 mmol L~(-1)with a correlation coefficient of 0.9992, a low detection limit of 0.48 mmol L~(-1) and a high sensitivity of 191.22μA(mmol L~(-1))~(-1)cm~(-2)(signal/noise, S/N = 3). Moreover, the non-enzymatic biosensor shows an excellent selectivity. 相似文献
8.
Gamil A. El-Shobaky Abd El-Mohsen M. Turky 《Colloids and surfaces. A, Physicochemical and engineering aspects》2000,170(2-3):161-172
The effects of doping of Co3O4with MgO (0.4–6 mol%) and V2O5 (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H2O2 at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V2O5 doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co3O4 solid. Treatment of Co3O4 with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H2O2 decomposition, of Co3O4 was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40°C on Co3O4 due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V2O5-doping of Co3O4 brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V2O5-doped Co3O4 solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO3+–CO2+ ion pairs and created Mg2+–CO3+ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H2O2. V2O5-doping exerted an opposite effect via decreasing the number of CO3+–CO2+ ion pairs besides the possible formation of cobalt vanadate. 相似文献
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The specific adsorption of sulfate ions on Cr2O3 was studied by a radiotracer technique using 35S-labelled sulfuric acid in low concentrations (c<10–3 mol dm–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined.
It was found that the extent of adsorption is determined by the protonation of the surface sites, similar to other oxides
studied previously. A comparison of Cr2O3 and Al2O3 in this respect shows that the protonation of the former takes place at significantly lower pH values than that of the latter.
The indirect radiotracer study of the adsorption of chromate on Al2O3 was carried out using labelled sulfate ions as indicator species. The results obtained show that the adsorption strength
of chromate species is very low in comparison to sulfate ions and a regular Langmuir-like adsorption behaviour can be observed.
It is believed that the observations presented may contribute to a better understanding of the behaviour of surface layers
with a mixed oxide content.
Electronic Publication 相似文献
11.
Hassan Hosseini Monfared Azar Mohajeri Ali Morsali Christoph Janiak 《Monatshefte für Chemie / Chemical Monthly》2009,17(1):1437-1445
Abstract
The Mn(II) dicarboxylate coordination polymers [Mn(μ-terephthalate)(H2O)2] n , [Mn(μ-oxalate)(H2O)2] n , and [Mn(μ-d-(−)-tartrate)] n were prepared in water and characterized by FT-IR spectroscopy and CHN analysis. Particles of the terephthalate catalyst were also synthesized, by reaction of terephthalic acid and MnCl2·4H2O by a sonochemical method. The catalytic potential of these coordination polymers as slow-release sources of catalytically active Mn species was tested in the oxidation of cyclooctene to its epoxide in acetonitrile, using hydrogen peroxide as oxygen source. For the terephthalate species the catalytic activity was found to increase with increasing dielectric constant and dipole moment of the solvent (being highest in acetonitrile), with reaction temperature to a maximum at 60 °C, and with an imidazole co-catalyst (highest activity found for a imidazole-to-catalyst molar ratio of 20:1). Good activity with more than 64% conversion in 24 h was obtained for epoxidation of cyclooctene and cyclohexene, whereas low yields only were obtained from aryl-substituted olefins. Some exo versus endo regioselectivity was found for norbornene. 相似文献12.
János Halász Alida Éll Dóra Méhn Edit Meretei Imre Kiricsi 《Reaction Kinetics and Catalysis Letters》2001,74(2):371-376
Ti- and V-containing MFI, MEL and MCM-41 catalysts were studied in the oxidation of cyclohexane, cyclohexene, naphthalene, tetralin, decalin and phenol with H2O2. Although TS-1 and TS-2 exhibited the highest activity and selectivity in the oxidation of
n
-hexane and 1-hexene, cyclohexene could only be oxidized effectively on the MCM-41 silicates. Since the oxidation of condensed aromatic systems over Ti- and V-containing MFI and MEL zeolites runs to difficulties, MCM-41 type catalysts may be offered for these reactions. 相似文献
13.
研究了一些氧化物的H2-TPR及CO-TPR行为,结果发现,Co3O4/Al2O3,NiO/SiO2,NiO和Pd/NiO的H2-TPR温度要低于它们的CO-TPR温度,特别是Pd/NiO样品,它的H2-TPR温度为598K,而其CO-TPR温度高达949K,差别为351K,因此有可能利用Pd/NiO在一定温度下选择性地与CO中的H2反应而将其除去. 实验结果表明,Pd/NiO可在603K及4000h-1的条件下从H2(0.34%),CO(50%)和N2(余)的混合气中选择性地除去90%以上的H2,吸氢容量为每克样品55mL标准态H2. 相似文献
14.
Alkenes a–d interact at ?80°C in 15 min. with the Vilsmeier reagent (Me2N=CHCl)+PO2Cl2? in presence of 30% H2O2 to yield the corresponding epoxides a–d. The reaction could involve the formation of the highly reactive hydroperoxymethylenedimethylammonium salt (Me2N=CHOOH)+PO2Cl?2. 相似文献
15.
Wei Zheng Xiaofeng Lu Wei Wang Zhenyu Li Hongnan Zhang Zhaojie Wang Xiuru Xu Shangyu Li Ce Wang 《Journal of colloid and interface science》2009,338(2):366-370
In this paper, we presented a simple and effective solution route to deposit Pt nanoparticles on electrospun In2O3 nanofibers for H2S gas detection. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). The results showed that large quantities of In2O3 nanofibers with diameters about from 60 to 100 nm were obtained and the surface of them was decorated with Pt nanoparticles (5–10 nm in size). The In2O3 nanofibers decorated by Pt nanoparticles exhibited excellent gas sensing properties to H2S, such as high sensitivity, good selectivity and fast response at relatively low temperature. 相似文献
16.
P.Veeraraghavan Ramachandran Bodhuri PrabhudasDebarshi Pratihar J.Subash ChandraM.Venkat Ram Reddy 《Tetrahedron letters》2003,44(19):3745-3748
The synthesis of the C7C21 fragment of epothilone A involving asymmetric alkoxyallyl- and crotylboration using α-pinene-derived reagents is described. 相似文献
17.
N. I. Kuznetsova A. S. Lisitsyn V. A. Likholobov 《Reaction Kinetics and Catalysis Letters》1989,38(1):205-208
Conditions are found for the preparation of Pt catalysts providing the formation of epoxy-derivative in the reaction of cyclohexene with an O2/H2 mixture.
Pt .相似文献
18.
Yingpu Bi 《中国科学:化学(英文版)》2023,(5):1239-1240
<正>Hydrogen peroxide(H2O2) is a chemical that is widely of interest in both environmental and energy fields. On the one hand, as a clean oxidant, H2O2 has been commonly used in the field of bleaching, disinfection, and advanced oxidation processes. On the other hand, H2O2 has also been explored as a liquid fuel alternative to H2 or fossil fuels in fuel cells due to its high energy density. However, the current ind... 相似文献
19.
Nicola Pinna Markus Antonietti Markus Niederberger 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):211-213
The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V2O3 and Nb2O5. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V2O3 crystals exhibit particle sizes between 20 and 50 nm, and the Nb2O5 crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character. 相似文献
20.
利用溶胶-凝胶法合成纳米NiCo2O4,并利用X射线衍射和透射电镜分析其结构和表面形貌. 结果表明NiCo2O4具有尖晶石结构, 平均粒径约为15 nm. 利用电势线性扫描和恒电势法测定了其对H2O2在碱性溶液中电化学还原反应的催化性能. 发现NiCo2O4对H2O2电化学还原具有高的催化活性和稳定性, 在H2O2浓度低于0.6 mol·L-1时, 其电化学还原反应主要通过直接还原途径进行. 以NiCo2O4为阴极催化剂的Al-H2O2半燃料电池在室温下的开路电压达1.6 V; 在1.0 mol·L-1 H2O2溶液中, 峰值功率密度达209 mW·cm-2, 此时电流密度为220 mA·cm-2. 相似文献