共查询到20条相似文献,搜索用时 15 毫秒
1.
Nasr-Allah M Deraz 《Thermochimica Acta》2003,401(2):175-185
Mn/Fe mixed oxide solids doped with Al2O3 (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (SBET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N2 adsorption isotherms and CO oxidation by O2. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn2O3 interacted readily with Fe2O3 to produce well-crystallized manganese ferrite (MnFe2O4) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al2O3-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al2O3 followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and SBET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al2O3 added, due to the enhanced formation of MnFe2O4 phase which is less reactive than the free oxides (Mn2O3 and Fe2O3). The activation energy of formation (ΔE) of MnFe2O4 was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe2O4 was attributed to an effective increase in the mobility of reacting cations. 相似文献
2.
Yun Guo Shuben Li Bin Zhang Jianzhong Niu Qiang Gao Ling Gao 《Reaction Kinetics and Catalysis Letters》2000,69(1):153-159
The influence of ZrO2 on the properties of Al2O3 and performances of Pd/Al2O3 catalyst in CO oxidation have been investigated. TPD results show that the activity enhanced is due to the increase of the adsorptive capacity of CO and the activation of C=O bond after the introduction of ZrO2. 相似文献
3.
Zr对CuO/ZnO/Al_2O_3前驱体物相、催化剂结构及其合成甲醇性能的影响 总被引:1,自引:0,他引:1
采用并流共沉淀法,在CuO/ZnO/Al2O3三元催化剂中加入第四组分Zr,考察了沉淀温度对四元催化剂的前驱体物相组成及浆态床合成甲醇催化活性的影响。通过XRD、DTG、TPR、FTIR、CO-TPD、XPS、HR-TEM等对所制备催化剂及其前驱体的微观结构进行了表征。研究表明:Zr促进了绿铜锌矿(Cu,Zn)5(CO3)2(OH)6物相的生成,使催化剂前驱体中绿铜锌矿含量增加,焙烧后的催化剂铜锌协同作用增强,CuO分散度提高,CuO晶粒平均直径只有4.18nm,同时还原温度显著降低为150℃,CO吸附能力增强,结果显著提高了浆态床合成甲醇催化活性和稳定性。与CuO/ZnO/Al2O3三元催化剂相比,80℃沉淀制备的含4%Zr的CuO/ZnO/Al2O3/ZrO2四元催化剂的甲醇时空收率提高了8.67%,失活率降低了65.12%。 相似文献
4.
Hyoung Lim Koh Sang Ho Lee Kyung Lim Kim 《Reaction Kinetics and Catalysis Letters》2000,71(2):239-244
The effect of MoO3 addition to alumina supported vanadia catalysts on the catalytic activity for the selective catlaytic reduction of NO is investigated. Upon the addition of MoO3, catalytic activity is enhanced and the particle size of V2O5 which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO3-V2O5/Al2O3 catalyst also exhibits more resistance to SO2 deactivation than V2O5/Al2O3 does. 相似文献
5.
Pedro de Lima Neto Mohamed Atik Luis A. Avaca Michel A. Aegerter 《Journal of Sol-Gel Science and Technology》1994,2(1-3):529-534
Sol-gel thin coatings of ZrO2, SiO2, 70SiO2-30TiO2 and 88SiO2-12Al2O3 compositions (mole %) have been prepared from sonocatalyzed sols and deposited by dip-coating technique on 316L stainless steel foils. The influence of the coatings on the chemical corrosion of the substrate has been measured through potentiodynamic polarization curves in aqueous 15% H2SO4 solution between 25 and 50°C. The values of the corrosion potential, polarization resistance and corrosion rate have been determined. Analysis of the data combined with scanning electron microscopy studies indicate that the films act as a geometric blocking against exposure to the corrosive media and increase the lifetime of the substrate up to a factor 8.5. 相似文献
6.
Nano‐ and microcomposite Al2O3‐ZrO2 coatings were deposited on various substrates in a sol‐gel ceramic paint by a supercentrifugal force and a gradual sintering process. Fine metal oxide powders were dispersed in a sol‐gel solution by superpower ball milling so as to form a uniform stable ceramic paint. High‐resolution microscopy (FE‐SEM) was used to characterize the coating, indicating that the coating is composed of composite particle clusters with an average diameter of ~1 µm. The clusters consisted of larger particles with an average diameter of ~0.5 µm in center and smaller particles of ~100 nm surrounding the larger ones. The coating was relatively dense and increasingly dense toward the substrate surface. 相似文献
7.
Sergio Cava Renata Benincá Sergio M. Tebcherani Iedo A. Souza Carlos A. Paskocimas Elson Longo José A. Varela 《Journal of Sol-Gel Science and Technology》2007,43(1):131-136
Al2O3 and Al2−x
Cr
x
O3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution
of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy
(reflectance spectra and CIEL*a*b* color data). The obtained results allow to identify the γ-Al2O3 to α-Al2O3 phase transition. The single-phase α-Al2O3 powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and
ruby luminescence lines observed for the powders of Al2−x
Cr
x
O3 are related to the γ to α-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium content. 相似文献
8.
E. Marin L. Guzman A. Lanzutti L. Fedrizzi M. Saikkonen 《Electrochemistry communications》2009,11(10):2060-2063
In the last 30 years, thin hard coatings were intensively investigated due to their high-performance characteristics: high wear resistance, low friction coefficient and good thermal stability. Performances were furthermore improved using multilayer configurations, although often limited by feasibility or cost considerations. One of the main problems to overcome was the low corrosion protection that these coatings assure to the tool steel substrates on which they are applied. To assure high performances and corrosion protection it is possible to employ a completely new approach, suitable either as a pre-treatment of the substrate or as top coating, by using materials of different nature in the form of nano-layers.Monolayer and multilayer coatings obtained by PVD (Physical Vapor Deposition, using reactive arc evaporation) and by PVD + ALD (Atomic Layer Deposition) were studied and compared. Both in-depth composition and corrosion resistance properties were investigated using SEM–EDXS, GDOES (Glow Discharge Optical Emission Spectrometry) and polarization curves in a 0.2 M NaCl solution. The coatings studied were a TiAlN/TiN bi-layer and a TiCN monolayer obtained by PVD and an Al2O3 nano-layer obtained by ALD. 相似文献
9.
制备了Ni负载量为15%的3种催化剂Ni/Al_2O_3、Ni/SiO_2、Ni/ZrO_2,考察了其在1,4-丁炔二醇加氢反应中的催化性能,结合XRD、H_2-TPR、H_2-TPD、N_2物理吸附等表征,研究了载体性质对催化剂1,4-丁炔二醇加氢性能的影响.结果表明,Ni/SiO_2催化剂上,由于Ni与SiO_2间弱的相互作用,Ni物种主要以大晶粒形式存在,产生大量弱吸附H_2物种,有利于低温下1,4-丁炔二醇加氢,在温度50℃,氢气压力1 MPa时,反应2 h可实现1,4-丁炔二醇的完全转化,1,4-丁烯二醇和1,4-丁二醇选择性分别达到68.1%与18.2%.Ni/Al_2O_3中Ni与载体间具有强相互作用,主要存在Ni-Al_2O_3界面或溢流到Al_2O_3载体表面的强吸附H_2物种,而Ni表面的弱吸附H_2物种较少,催化加氢活性明显降低.Ni/ZrO_2中由于还原过程中ZrO_2的迁移包裹作用,Ni表面低温吸附H_2物种最少,活性最低,1,4-丁炔二醇转化率仅为8.1%,主产物为1,4-丁烯二醇. 相似文献
10.
M.A. Flores-Gonzalez S. Roux P. Perriat O. Tillement 《Journal of solid state chemistry》2005,178(4):989-997
Sub-micrometer Tb-doped Y2O3 luminescent powders were prepared from nitrate precursors using the polyol method. Just after precipitation, the powders consist of agglomerates with a spherical shape and a size ranging between 400 and 500 nm. Each agglomerate is composed of ultra-small crystallites (from 3 to 6 nm) of a bcc oxide phase whose luminescence presents original features in comparison with bulk materials. Powders were further calcinated at different temperatures and for annealing below 900 °C, highly crystalline samples with the classical green 5D4→7F5 luminescent transitions of Tb3+ ions are obtained. For optimized annealing temperatures, sintering between the agglomerates is avoided and a sub-micrometric powder with a narrow size distribution and a high luminescence is obtained. 相似文献
11.
The chemisorption of CO2 has been studied on alumina-supported Co-and Ni-promoted molybdenum-oxide (CoMo, NiMo) and, besides those, on monometallic
Co and Ni. Chemisorbed amounts on the monometallic samples were equal to that on the alumina support. XPS measurements were
performed with the NiMo and Ni samples. The amounts of surface Mo-and Al-ions were calculated. It could be established that
molybdenum oxide forms a near to monomolecular layer on the Co-and Ni-promoted molybdena-alumina samples. 相似文献
12.
Satoshi Sumiya Mika Saito Masataka Furuyama Nobutsune Takezawa Kiyohide Yoshida 《Reaction Kinetics and Catalysis Letters》1998,64(2):239-246
The Ag/Al2O3 catalyst supported on cordierite honeycomb (Ag/Al2O3/ cordierite) is highly active forthe reduction of lean NOx by ethanol. Addition of H2O enhances the NOx reduction to CO2 and N2, and suppresses the formation of by-products such as CO, CH3CHO and C2H4. 相似文献
13.
Effect of K promotion on the CO hydrogenation activity and selectivity of coprecipitated Co/Al2O3 has been studied. K addition is found to lower total activity while enhancing C2-C4 olefins selectivity; kinetic data indicate that the reaction mechanism is not affected. 相似文献
14.
15.
Hashem Sharghi Zahra Shahsavari-Fard 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2491-2501
A new facile method for thia-Fries rearrangement of arylsulfonates has been developed. A variety of arylsulfonates rearrange in excellent yields in the presence of Al2O3/MeSO3H as a new reagent without the use of any solvent. 相似文献
16.
Zinc ferrite nano-powders with a nominal composition of ZnFe2O4 were prepared by combustion synthesis using mixture of urea and ammonium nitrate as fuel. The influence of alumina-doping on the structural, morphological and magnetic properties of ZnFe2O4 nano-particles was investigated by means of X-ray powder diffraction (XRD), infrared (IR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and vibrating sample magnetometer (VSM). XRD and IR analyses confirm the cubic spinel phase of ZnFe2O4 nano-particles. The Zn ferrite presented a uniform microstructure with grain size in nano-scale. Alumina-doping brought about a change in the morphology of the as prepared ferrite from sphere-like to regular hexagon. Al2O3-treatment led to a decrease in the coercivity (Hc), magnetization (Ms) and magnetic moment (nB) of the investigated system. The maximum decrease in the values of Hc, Ms and nB due to the treatment with 1.5 wt% Al2O3 attained 13.5, 17.4 and 13.5%, respectively. The observed results can be explained on the basis of particle size and the Fe3+ concentration in the octahedral and tetrahedral sites involved in the cubic spinel structure. 相似文献
17.
Shemseddine Fessi Abdelhamid Ghorbel 《Journal of Sol-Gel Science and Technology》2003,26(1-3):837-841
In this work, the metal dispersion of the Pd/Al2O3 catalyst prepared by sol-gel method is improved by an adequate optimisation of the preparative variables. First, the gelation temperature and the ageing time are selected, in order to avoid the reduction of the metal precursor (palladium acetylacetonate, Pd(acac)2) by the solvent (sec-butanol, sB). The metal sintering effect on the catalysts treated in oxygen at 500°C is then minimized when the alumina pore size is controlled by the variation of the alumium alkoxide (AsB) concentration and the acetic acid amount ([AcA]/[AsB]). The appearance of new palladium particles on the alumina surface and the matching between the particle diameters and the pore sizes were also effective for the metallic surface area improvement on the samples treated in oxygen at 800°C. Compared to the reference catalysts, the higher metal dispersion obtained on the sol-gel ones was the determinant factor for their higher catalytic activity in methane combustion. 相似文献
18.
An optical pyrometer is used to measure and, in conjunction with temperature programmer and controller, control the temperature of the NETSZSCH Dilatometer DIL 402 E/7 up to 2400°C. This instrument is thus suitable to investigate sintering of technical ceramic materials such as SSiC and ZrO2. Measurements carried out on these materials containing organic additives show that the sintering range of SSiC starts at 1800°C—although its final density is not reached at 2400°C at a heating rate of 20 deg·min?1—and that the densification of ZrO2 occurs between 1000° and 1800°C. Using rate controlled sintering (RCS) the sintering process can be extended on a time scale, but the same densities are obtained at the same temperatures when comparing the measurements with and without RCS. 相似文献
19.
E. Castro Luna A. M. Becerra M. I. Dimitrijewits 《Reaction Kinetics and Catalysis Letters》1999,67(2):247-252
The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using
Rh-promoted Ni/Al2O3 catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted
catalysts showed an increase in CH4 reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase
in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al2O3. 相似文献
20.
In this study, the reaction conditions of poly-4-[(2-methylphenyl)iminomethyl]phenol (P-2-MPIMP) were studied by using oxidants such as air O2, H2O2 and NaOCl in an aqueous alkaline medium between 50 and 90 °C. The structures of the synthesized monomer and polymer were confirmed by FT-IR, UV-vis, NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of poly-4-[(2-methylphenyl)iminomethyl]phenol (P-2-MPIMP) was found to be 20% (for air O2 oxidant), 33% (for H2O2 oxidant), and 74% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of P-2-MPIMP were found to be 3300, 4100 g mol−1 and 1.242, using H2O2, and 4550, 5150 g mol−1and 1.132, using air O2 and 5300, 5850 g mol−1 and 1.104, using NaOCl, respectively. According to TG analysis, the weight losses of 4-[(2-methylphenyl)iminomethyl]phenol (2-MPIMP) and P-2-MPIMP were found to be between 75.29% and 48.17% at 1000 °C, respectively. P-2-MPIMP was shown to have a higher stability against thermal decomposition. Also, electrical conductivity of the P-2-MPIMP was measured, showing that the polymer is a typical semiconductor. Electrochemically, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and electrochemical energy gaps ( of 2-MPIMP and P-2-MPIMP were found to be −6.01, −6.03; −2.63, −2.82; 3.38 and 3.21 eV, respectively. According to UV-vis measurements, the optical band gap (Eg) of 2-MPIMP and P-2-MPIMP was found to be 3.40 and 2.97 eV, respectively. 相似文献