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11.
Masaru Ogura 《Catalysis Surveys from Asia》2008,12(1):16-27
A composite silicate material, which possesses the characteristics of both microporous zeolite and mesoporous silica materials,
is developed by top–down and bottom–up synthesis techniques. In order to realize a micro- and mesoporous composite material,
several essential points must be clarified, since each porous material is synthesized under very different metastable conditions:
zeolite is a silicate crystal, while the wall of mesoporous material is composed of amorphous silicate. Here, some aspects
of the realization of a micro- and mesocomposite porous material are described, as are our experimental results regarding
the successful production of composite catalyst. 相似文献
12.
J. Goering Shweta Sah U. Burghaus K. W. Street Jr. 《Surface and interface analysis : SIA》2008,40(11):1423-1429
JSC‐1a (a simulated lunar dust sample) supported on a silica wafer (SiO2/Si(111)) has been characterized by scanning electron microscopy (SEM), energy dispersive x‐ray (EDX) spectroscopy, and Auger electron spectroscopy (AES). The adsorption kinetics of water has been studied primarily by thermal desorption spectroscopy (TDS) and in addition by collecting isothermal adsorption transients. Blind experiments on the silica support have been performed as well. JSC‐1a consists mostly of aluminosilicate glass and other minerals containing Fe, Na, Ca, and Mg, as characterized in detail in prior studies, for example, at NASA. The particle sizes span the range from a few micrometers up to 100 µm. At small exposures, H2O TDS is characterized by broad (100–450) K structures; at large exposures, distinct TDS peaks emerge, which are assigned to amorphous solid water (ASW) (145 K) and crystalline ice (CI) (165 K). Water dissociates on JSC‐1a at small exposures but not on the bare silica support. Coadsorption TDS data (alkane–water mixtures) indicate that rather porous condensed ice layers form at large exposures, with the mineral particles acting most likely as nucleation sites. At thermal impact energies, the initial adsorption probability amounts to 0.92 ± 0.05. It is evident that the drop‐and‐dry technique, developed in studies about nanoparticles/tubes, can be extended to obtain samples for surface science studies based on powders consisting of particles with rather large diameters. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
CHEN Yan-ping LUO De-li HUANG Bin CHENG Hao TANG Xian-chen LI Qiang LEI Hong-bo CHEN Dan-ping 《光谱学与光谱分析》2021,41(6):1863-1868
采用熔融-淬冷法制备了Tb3+掺杂锂铝硅酸盐闪烁玻璃,用紫外激发光谱、发射光谱及荧光寿命表征了光致发光性能,用X射线和阴极射线激发测试了辐射致发光性能。研究结果表明:低Tb3+掺杂浓度时,随着其浓度增大,Tb3+间的交叉弛豫增加导致了5D3→7Fj跃迁的能量逐渐向5D4→7Fj迁移转变,5D3激发态的荧光寿命和发射强度均明显下降,5D4-7Fj发射强度逐渐增大。较高Tb3+浓度时,其浓度继续增加会提升非辐射比例,是荧光寿命降低和荧光猝灭的最主要原因。比较光致发光和辐照致发光性能,发现随着激发源的能量上升,会增加激发态5D3能级向5D4能级的能量转移,同时,由于玻璃的密度低会导致辐照致发光效率随激发源的能量上升而下降。 相似文献
14.
The dc field rheological properties and frequency dependent dielectric properties of a set of electrorheological (ER) fluids composed of oxidized polyacrylonitrile or aluminosilicate materials dispersed in silicone oil were examined in this paper. Our experimental investigations show that there is a complicated relationship between the dielectric properties of dispersed particles and the ER effect. The dielectric loss of dispersed particles, which has not attracted much attention in previous work, was found to play a considerable role in ER response. The large dielectric loss tangent, experimentally around 0.10 at 1000 Hz, is found to be needed for a strong ER effect. A good ER solid material should first have large dielectric loss, and then the higher the dielectric constant, the stronger the ER effect. The large dielectric loss would facilitate the turning of dispersed particles, and the high dielectric constant would maintain the fibrillation structure stable and strong. Two processes, the particle turning process and the particle polarization process, are thought to be involved in ER activity. Our findings, in connection with the Wagner model, can better explain why the strongest ER effect occurs at particle conductivity of 10−7S/m; why the shear stress of some ER fluids decreases with frequency while with others the shear stress increases with frequency; and why trace water can enhance the ER effect considerably, which would help in understanding the mechanism of the ER effect. Too large a dielectric loss is thought to be unfavorable for the ER effect, and its suitable range is worth further study. The results also present a method of designing high performance ER fluids, which would significantly promote development of electrorheology and its application in industrial areas. 相似文献
15.
间、对-甲基异丙苯是生产间、对-苯酚的反应中间体,因此其制备受到国内外广泛关注.ZSM-5,Y型,betn等沸石分子筛和掺杂zn的Al-MCM-41介孔分子筛在此反应中表现出不同的择形性.近年来利用沸石分子筛前驱体自组装技术合成的新型介孔材料已显示出优异的催化性能, 相似文献
16.
Laby L. Klein L.C. Turniansky A. Avnir D. 《Journal of Sol-Gel Science and Technology》1997,10(2):177-184
Using the sol-gel process, we prepared two types of xerogels. Thin, transparent, crack-free alumina disks were prepared from aluminum tri-secondary butoxide (ASB). Addition of partially hydrolyzed tetraethylortho-silicate (TEOS) to such alumina sols produced translucent, warped silica-containing alumina xerogels. While the pure alumina xerogels were water soluble, addition of silica improved their durability. To understand the change in water solubility, we investigated the chemical and structural changes that occurred when silica was added. Characterization was performed using X-ray diffraction analysis, thermal analysis, nitrogen sorption analysis and 27Al NMR spectroscopy. 相似文献
17.
Feng-Shou Xiao 《Catalysis Surveys from Asia》2004,8(3):151-159
Microporous zeolites are widely used commercial catalysts, but their applications are intrinsically limited by their small channel diameters. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS and SBA-15. These mesoporous materials have pore diameters of 30–60 Å and exhibit catalytic properties for the catalytic conversion of bulky reactants, but unfortunately, when compared with microporous zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. We review here that the assembly of preformed zeolite precursors with surfactants can synthesize a series of ordered mesoporous materials, which include (1) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (2) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (3) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (4) hydrothermally stable mesoporous ferrisilicates. This work would open a door for the industrial application of mesoporous materials as catalysts for large molecules. 相似文献
18.
The ordered mesoporous aluminosilicate molecular sieve (MASMS-1) stable in the high-temperature steam has been successfully synthesized from the assembly of diluted ZSM-5-type precursor with mesoporous MCM-41. The material was characterized by XRD, N2 adsorption-desorption, FE-SEM, TEM, FT-IR spectroscopy and 27A1 MAS NMR techniques. This mesoporous material shows high stability in the high-temperature steam [H2O (φ=20%) in N2 at 800 ℃ for 4 h], which might be ascribed to the synergistic effect of both thick walls containing zeolite-like five-membered ring subunits and highly condensed surface silanol groups. 相似文献
19.
Tailor and Control of Acidic Strength in Ordered Mesoporous Aluminosilicates by Using Preformed Zeolite Precursors 总被引:1,自引:0,他引:1
The acidic strength of ordered mesoporous aluminosilicates of MAS-2, MAS-3, MAS-7 and MAS-9 and microporous crystals of Y, L, beta, and ZSM-5 zeolites was systemically investigated by temperature-programmed desorption of ammonia (NH3-TPD). Due to the use of preformed zeolite precursors of Y, L, beta and ZSM-5, the ordered mesoporous aluminosilicates with distinguished acidic strength were obtained, being dependent on the type of preformed zeolite precursors. Therefore, the acidic strength of these mesoporous aluminosilicates could be tailored and controlled. 相似文献
20.
Barbara Pacewska I. Wilińska M. Bukowska G. Blonkowski Wiesława Nocuń-Wczelik 《Journal of Thermal Analysis and Calorimetry》2004,77(1):133-142
The so-called pozzolanic activity of waste catalysts from fluidised cracking was investigated. For this purpose a series of
cement mixtures with this waste material were prepared and subsequently the pastes and mortars were produced. Waste aluminosilicate
catalyst was used both in raw form and after grinding in a ball mill for 60 min. The hydrating mixtures were subjected to
the calorimetric measurements in a non-isothermal/non-adiabatic calorimeter. After an appointed time of curing the hydrating
materials were studied by thermal analysis methods (TG, DTG, DTA). The pozzolanic activity factors were determined, basing
on the compressive strength data. The increased activity of cement — ground pozzolana systems has been thus proved. An accelerated
Ca(OH)2 consumption as well as higher strength were found for materials containing ground waste catalyst, as compared to those, mixed
with the raw one. Thus grinding was also proved to result in mechanical activation in the case of the waste catalyst from
fluidised cracking.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献