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91.
The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H2S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al2O3 and Pt/Al2O3. In the absence of H2S in the feed, Pt/SnO2appears as a very promising catalyst for CH4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al2O3. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO2 is slightly less resistant than Pd/Al2O3. In the presence of H2S, Pt/SnO2catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2sites active in CH4oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2. 相似文献
92.
The factors affecting the adsorption and desorption kinetics in a TEOM are reviewed in detail with particular attention given to the assumptions required to obtain physical transport parameters from the data. Two models are presented to simulate TEOM adsorption data in the case that concentration differences down the catalyst bed can be neglected, as is appropriate when the amount of catalyst used is small, the carrier gas flowrate is large, and/or the adsorbate partial pressure is low. In the first model, the effective diffusion coefficient, De, is taken to be constant. In the second model, the effective diffusion coefficient is assumed to obey the Darken equation, De=D0/(1−θ). The TEOM results obtained on n-hexane, n heptane, n-octane, toluene and p-xylene on a commercial FCC catalyst and on pure rare-earth exchanged zeolite Y under non-reacting conditions (373-) are analysed in detail. It is found that intracrystalline diffusion is not the limiting factor affecting the overall rates of adsorption and desorption for the systems studied. Instead, it is the transport of molecules between the adsorbed and vapour phases at the edge of zeolite crystallites that is the limiting transport step affecting the overall kinetics. For the FCC catalyst, the limiting step is the transport of molecules at the zeolite-matrix interface rather than, say, the matrix-vapour interface. Local rate constants for the desorption of the hydrocarbons at the rate-controlling interface have been obtained. 相似文献
93.
Céline Cohen Rory Giles Victoria Sergeyeva Nitesh Mittal Patrick Tabeling Djamal Zerrouki Jean Baudry Jérôme Bibette Nicolas Bremond 《Microfluidics and nanofluidics》2014,17(5):959-966
The capacity of microfluidic technology to fabricate monodisperse emulsion droplets is well established. Parallelisation of droplet production is a prerequisite for using such an approach for making high-quality materials for either fundamental or industrial applications where product quantity matters. Here, we investigate the emulsification efficiency of parallelised drop generators based on a flow-focusing geometry when incorporating the role of partial wetting in order to make emulsion droplets with a diameter below 10 μm. Confinement intrinsically encountered in microsystems intensifies the role played by interfaces between liquids and solids. We thus take advantage of partial wetting to enhance the maximum confinement accessible due to liquid flow focusing. We compare the performances brought by partial wetting to more established routes such as step emulsification. We show that the step configuration and the partial wetting regime are both well suited for being parallelised and thus open the way to the production of fine and calibrated emulsions for further applications. Finally, this new route of emulsification that exploits partial wetting between the fluids and the channel walls opens possibilities to the formation of substantially smaller droplets, as required in many fields of application. 相似文献
94.
Reading frame selection of nucleic acids has important implications for protein engineering and genomics. Current methods are limited because selection of the gene of interest inevitably depends on the solubility of its translated product. Here we report the construction of the pInSALect vector, which provides strict reading frame selection without concomitant selection for protein solubility or folding. This plasmid incorporates the cis-splicing VMA intein sequence from Saccharomyces cerevisiae to facilitate the post-translational self-excision of the protein of interest, thereby eliminating potential aggregation problems. Results from two libraries of chimeric glycinamide ribonucleotide formyltransferases confirm the superior performance of pInSALect over existing reading frame selection systems. 相似文献
95.
A semitheoretical correlation based on an extension of the random length, random angle statistical model of Davidson (1959) is developed which predicts liquid film mass transfer coefficients in a column packed with partially wetted Raschig rings. The method takes into account the ring size and the mixing which occurs at the packing junctions and allows an estimation of the effective length of a packing piece for a particular liquid viscosity. Predicted values of mass transfer coefficients are in good agreement with the experimental values obtained for the carbon dioxide-water and carbon dioxide-aqueous glycerol systems at 25°C reported by Mangers and Ponter (1980b) and other systems reported by Sherwood and Holloway (1940). 相似文献
96.
PVC profile extrusion compounds have a unique morphology. While other polymers gradually decrease in extrusion die swell with increasing length/thickness (L/D) ratio, PVC profile extrusion compounds have a low die swell, quite independent of the die's L/D ratio in the range of 5 to 20. The fact that the die land length can be changed without changing the extrudate swell is an important consideration, which makes die design and balancing dies simpler and easier for PVC profile extrusion compounds. While other polymers substantially increase extrudate swell with increased shear rate, the swell of the PVC profile compounds is not much affected by shear or extrusion rate. This unique behavior allows wider processing latitude in profile extrusion and faster extrusion rates than with other polymers. Another unique factor in the rheology of PVC profile extrusion compounds is that extrusion die swell increases with increasing melt temperature, while other polymers have decreasing die swell with increasing melt temperature. The unusual rheology of PVC profile extrusion compounds is attributed to its unique melt morphology, where the melt flow units are 1 um bundles and molecules that have low surface to surface interaction and entanglement at low processing temperatures but increased melting and increased entanglement at higher processing temperatures. Other polymers, unlike PVC, have melt flow at the molecular level. 相似文献
97.
The purpose of this work was to examine the possible significance in the formation of metallurgical coke of the anisotropic spherical mesophase exemplified by that found during the carbonization of pitch-like materials, and to ascertain if the various types of optical anisotropy found in coke could form a basis for the characterization of cokes produced from different coals. Vitrains from a wide range of coals were carbonized at temperatures from 370 to 1000 °C and the types and amounts of optical anisotropy in the resulting semi-cokes and cokes were determined from microscopic examination, the anisotropic components being classified according to grain size of the granular mosaics and appearance. The anisotropy developed directly from the isotropic phase, appearing initially as a fine-grained mosaic. With increasing carbonization temperature, this fine-grained mosaic was transformed into progressively coarser-grained anisotropy, the extent of this transformation depending on the rank of the vitrain. It is therefore concluded that the formation, growth and coalescence of anisotropic spherical bodies, such as occurs during the carbonization of pitch, is not a necessary precursor of the mosaic anisotropy in coke. The type and amount of anisotropy developed provide a quantitative means of characterising different cokes. 相似文献
98.
The distribution of plasmalogenase for the hydrolysis of 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (plasmenylethanolamine) in the subcellular fractions of guinea pig tissues was examined. Plasmalogenase
activity was found in high abundance in the cytosolic fractions of the brain and the heart. Assessment of microsomal marker
enzyme activities in the cytosolic fraction revealed that plasmalogenase activity in the cytosol was not due to microsomal
contaminations. The characteristics of the cytosolic plasmalogenase were very similar to the microsomal enzyme with respect
to the pH profile of the reaction, the presence of divalent cations and Km values for plasmenylethanolamine. However, the cytosolic enzyme was slightly less stable at 55°C than the microsomal enzyme.
Cytosolic enzyme activity was eluted as a broad peak in Sepharose 6B chromatography with an average molecular weight of 250,000.
Our results demonstrate that most of brain plasmalogenase activity is soluble which makes the brain cytosol an excellent source
to initiate the purification of this enzyme. 相似文献
99.
100.
PU YiFei SIARRY Patrick ZHOU JiLiu LIU YiGuang ZHANG Ni HUANG Guo LIU YiZhi 《中国科学:信息科学(英文版)》2014,(7):180-198
In this paper,a set of fractional partial differential equations based on fractional total variation and fractional steepest descent approach are proposed to address the problem of traditional drawbacks of PM and ROF multi-scale denoising for texture image.By extending Green,Gauss,Stokes and Euler-Lagrange formulas to fractional field,we can find that the integer formulas are just their special case of fractional ones.In order to improve the denoising capability,we proposed 4 fractional partial differential equation based multiscale denoising models,and then discussed their stabilities and convergence rate.Theoretic deduction and experimental evaluation demonstrate the stability and astringency of fractional steepest descent approach,and fractional nonlinearly multi-scale denoising capability and best value of parameters are discussed also.The experiments results prove that the ability for preserving high-frequency edge and complex texture information of the proposed denoising models are obviously superior to traditional integral based algorithms,especially for texture detail rich images. 相似文献