Platinum catalysts supported on silica, silica-alumina and alumina supports were prepared using four different cationic and anionic platinum precursors in order to examine the contribution of the precursors and supports to the platinum dispersion. The pH adjustment of the precursor suspension to obtain an opposing surface charge of the support to that on the platinum precursor ions considerably improved the platinum dispersion by strengthening their adsorption on the support. However, exceptional platinum dispersion was achieved, regardless of the precursor and support, by simultaneous pH adjustment and titania incorporation on the supports. The increase in the interaction between the platinum precursor and the titania-incorporated support raised the dispersion and stability of the platinum catalysts with high-loading, even after reduction at 400 °C. The physico-chemical states of platinum and titanium were investigated by XRD, TEM, XAFS spectroscopy and CO adsorption technique. The platinum catalysts supported on the titania-incorporated supports with pH adjustment exhibited highly dispersed platinum particles ranging in size from 1 to 3 nm. They also exhibited high catalytic activity in the oxidation of carbon monoxide because of its incorporated titania and partially oxidized, small platinum particles. 相似文献
Hard coatings were deposited on a polycarbonate plate using a sol–gel process with a melamine derivative, poly(vinyl alcohol) (PVA), and silicates and examined as potential substitutes for glass in cars. PVA was partially functionalized with (3-isocyanatopropyl)triethoxysilane, and the synthesized polymer was used to form a coating solution with methylated poly(melamine-co-formaldehyde), tetraethoxysilane, and methyltriethoxysilane. The coatings that contained both the melamine and silicate structures were deposited using a sol–gel process. The optimum conditions and formulation to obtain excellent physical properties of the coating were determined. Smooth coatings with the hardness of a 3H class pencil, excellent abrasion resistance and transparency were formed. 相似文献
This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of municipal secondary sludge. Sludge samples (500 g) were heated for 0, 3, 5, 7, 9, 11, and 15 min in a microwave oven (2450 MHz, 700 W). The solubilization degree (soluble chemical oxygen demand (SCOD)/COD) of sludge increased asymptotically with microwave irradiation time from 2% at 0 min to 22% at 15 min. The concentrations of soluble protein, carbohydrate, lipid, and calcium also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) of sludge increased from 3.58 to 4.77 g COD l−1. The results show that microwave irradiation increases the solubilization degree and BAP of municipal secondary sludge. 相似文献
Tailor made : We report the rational biosynthesis of C15 hydroxylated non‐quinone geldanamycin analogues by site‐directed mutagenesis of the geldanamycin polyketide synthase (PKS), together with a combination of post‐PKS tailoring genes. Rational biosynthetic engineering allowed the generation of geldanamycin derivatives, such as DHQ3 illustrated in the figure, which had superior pharmacological properties in comparison to the parent compound.
We investigated the dependence of unipolar diffusion charging of nanoparticles on the dielectric constant of the particle material experimentally. The examined nanoparticles (10–200 nm) cover a wide range of dielectric constant but have almost the same spherical or compact morphology. Measurements of both intrinsic charged fraction and mean charge per particle show very small differences among different materials. The level of the small difference is consistent with the estimation by Fuchs’ [(1963). On the stationary charge distribution on aerosol particles in bipolar ionic atmosphere. Geofisica Pura e Applicata, 56, 185–193] theory. 相似文献
We demonstrate that the nanoscopic block copolymer patterns on GaN can enhance light extraction efficiency of GaN-based light
emitting diodes. Nanoporous patterns were fabricated on a bare GaN substrate via self-assembly of poly(styrene-b-methyl methacrylate) block copolymers from which PMMA microdomains were selectively removed later on. A bare GaN surface
was treated with a photo-crosslinkable thin layer of poly(styrene-r-methyl methacrylate) random copolymers to tune the cylindrical microdomain orientations. The nanoporous block copolymer thin
film was controlled to be thicker than its typical repeat period in bulk by incorporating PMMA homopolymer into block copolymer.
Consequently, the light extraction efficiency in photoluminescence spectra could be tuned with the thickness of nanopatterned
thin film on GaN.
This paper is dedicated to Professor Chul Soo Lee on the occasion of his retirement from Korea University. 相似文献
Surfactant systems show highly non-ideal phase behavior because of the inter-association and intra-association hydrogen bond.
We present a lattice fluid equation of state that combines the multi-fluid nonrandom lattice fluid model with modified Veytsman
statistics for intra+inter molecular association to calculate phase behavior for mixture containing surfactant systems. The
literatureresults fitted to this model show good accordance for mixtures containing nonionic surfactant systems.
This article is dedicated to Professor Chul Soo Lee in commemoration of his retirement from Department of Chemical and Biological
Engineering of Korea University. 相似文献
The sensitivity of two-dimensional isothermal film casting processes to ongoing sinusoidal disturbances has been investigated
by using the frequency response method with transient simulation techniques. Amplitude ratios of state variables such as cross-sectional
area, film width and film thickness at the take-up position with respect to a sinusoidal disturbance show resonant peaks along
the frequency domain. Effects of operating conditions, such as drawdown ratio and aspect ratio, on the process sensitivity
have been examined. Increasing drawdown ratio and decreasing aspect ratio make the system more sensitive to disturbances.
Also, the dichotomous behavior in the sensitivity analysis using viscoelastic Phan-Thien and Tanner fluids has been elucidated.
This frequency response method can be a useful tool to optimally design process systems for better processability and product
quality.
This article is dedicated to Professor Chul Soo Lee in commemoration of his retirement from Department of Chemical and Biological
Engineering of Korea University. 相似文献
The preparation and microwave dielectric properties of ZnAl2O4-based glass–ceramic composites were investigated. Using zinc borosilicate (ZBS) glass and Al2O3, glass–ZnAl2O4 composites with high quality factor was successfully prepared at temperatures below 950 °C. The linear shrinkage for 50 vol% ZBS glass–ZnAl2O4 composite showed a steep increase up to 650 °C and a plateau between 700 °C and 950 °C, implying that one-stage densification process occurred. The crystallization of ZnAl2O4 was observed above 700 °C and an insufficient densification occurred due to the consumption of the glass. As the sintering temperature increased, the quality factor (Q × f0) showed an increase with an S-type curve whereas the dielectric constant was almost constant. The formation of ZnAl2O4 might correspond to the increase of Q × f0; a high value of 17,757 GHz (1415 at 12.6 GHz) was obtained for the specimen sintered at 900 °C. 相似文献
By carbothermally reducing a TiO2 core–sucrose shell precursor, titanium carbide mesoporous nanoparticles with a very high specific surface area (147 m2/g at 1500°C) have been prepared. The high specific surface area results from the mesoporous nature of the produced nanoparticles with two types of pores: the one with a pore diameter of about 20 nm and the other with <4 nm. 相似文献