Three dimensional (3-D) cubic KIT-6 with directly incorporated vanadium was hydrothermally synthesized by using Pluronic P123
and n-butanol as the structure-directing mixture, tetraethyl orthosilicate (TEOS) as the silica source and NH4VO3 as the vanadium source. The molar composition was varied in the range of 0.017 P123/0.08–2.4 V/1.0–2.0 TEOS/1.31–1.70 BuOH/1.83–3.00
HCl/195 H2O. The orderness of mesopore structure was estimated by X-ray diffraction, N2 adsorption, and TEM analysis. The effects of the amount of HCl, TEOS and BuOH on the structure of KIT-6 were discussed. The
time and temperature for the synthesis of KIT-6 were also optimized. The amount of vanadium content influenced the framework
structure and crystallinity of the Ia3d phase significantly. 相似文献
The direct incorporation of vanadium into the three-dimensional (3-D) cubic Ia3d mesostructure designated as V-KIT-6 was prepared,
and the material obtained therein showed a very high specific surface area of ∼1,000 m2/g with tunable pore diameters in a narrow distribution of sizes, ∼5.7 to 6.0 nm. The coordination and nature of the V sites
in V-KIT-6 were characterized by 51V-spin-echo NMR analysis. It shows that after calcination, the V4+ species are totally oxidized to the V5+ state with 4- and 6-coordinated V-O environments in a highly dispersed state with much less crystalline V2O5 formation. The calcined V-KIT-6 materials showed excellent catalytic activity in the direct oxidation of styrene using tert-butyl
hydroperoxide (TBHP) as an oxidant. 相似文献
The direct synthesis of three-dimensional (3-D) cubic V-KIT-6 was prepared using a Pluronic P123 triblock copolymer as the structure directing agent and n-butanol as the co-surfactant. The material obtained therein showed a very high specific surface area 1000 m2/g with pore diameters that could be tuned within a narrow size distribution of 5.7–6.0 nm. After calcination, Raman and UV–vis analysis revealed the presence of V5+ species in a highly dispersed state with much less crystalline V2O5 formation. 51V-NMR analysis showed that the vanadium species interacted directly with the silica framework in an almost symmetrical tetrahedral environment. NH3-TPD analysis for V-KIT-6 showed a wide distribution of acid sites at temperatures ranging from 200 to 800 °C. The calcined V-KIT-6 materials showed excellent catalytic activity in the direct oxidation of cyclohexane using dilute aqueous H2O2 as the oxidant. 相似文献
Nowadays secure medical image watermarking had become a stringent task in telemedicine. This paper presents a novel medical image watermarking method by fuzzy based Region of Interest (ROI) selection and wavelet transformation approach to embed encrypted watermark. First, the source image will undergo fuzzification to determine the critical points through central and final intensity along the radial line for selecting region of interest (ROI). Second, watermark image is altered to time-frequency domain through wavelet decomposition where the sub-bands are swapped based on the magnitude value obtained through logistic mapping. In the each sub-band all the pixels get swapped, results in fully encrypted image which guarantees the watermark to a secure, reliable and an unbreakable form. In order to provide more robustness to watermark image, singular values are obtained for encrypted watermark image and key component is calculated for avoiding false positive error. Singular values of the source and watermark image are modified through key component. Experimental results reveal that the proposed algorithm attains high robustness and improved security to the watermarked image against various kinds of attacks.
A series of vanadia-doped titania pillared clay (V/Ti-PILC) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H2S was investigated in this study. V/Ti-PILCs were characterized using X-ray diffraction (XRD), BET apparatus, and X-ray photoelectron spectroscopy (XPS). V/Ti-PILCs showed better catalytic performance than as such Ti-PILC at temperatures ranging from 220 to 300 °C without any considerable SO2 emission. The H2S conversion over V/Ti-PILC increased with increasing vanadia content up to 5 wt.%. This superior catalytic performance might be related to the uniform dispersion of vanadia in the form of monomeric and polymeric species. However, it decreased at 10 wt.% vanadia loading due to the decrease of surface area and to the formation of crystalline V2O5 phase. The presence of water vapor in the reactant mixture resulted in the decrease of the H2S conversion. 相似文献
Wireless Personal Communications - Healthcare has experienced significant growth in recent years, bringing both advantages and downsides. It is more difficult to provide a precise diagnosis using... 相似文献
A systematic study was carried out to examine the viable synthesis condition at high acidic condition for the direct incorporation of a high level of vanadium into the 3D cubic arrangement of SBA-16 molecular sieves. The extent of mesopore structural ordering was determined by X-ray diffraction, N2 physisorption, SEM and TEM analysis. The coordination and nature of the V sites were characterized by FT-Raman, electron spin resonance, 29Si nuclear magnetic resonance spectroscopy, UV–visible diffuse reflectance spectroscopy and NH3–TPD analysis. The surface area of calcined V-SBA-16 was ~1000 m2/g, while the mesopore volume of the SBA-16 cage ranged from 0.3 to 0.6 cm3g?1. The pore size distribution was ~3.0 nm with a wall thickness of ~9.7 nm at the maximum. The Si/V ratios as determined by ICP-OES technique was varied from 438 to 8, respectively. The calcined samples exhibited promising catalytic activity in the oxidation of styrene with tert-butyl hydroperoxide as an oxidant. 相似文献