Effects of Catalyst Heating Rates Upon the Activity of Silica-Supported Silicomolybdic Acid Catalysts for Methane Partial Oxidation

Silica-supported silicomolybdic acid (SMA) catalysts showed a very high activity for partial oxidation of methane into formaldehyde at 873 K in the presence of an excess amount of water vapor in feed. However, the high activity was observed only when the catalysts were heated to 873 K with very high heating rates such as 100 K min^-1. In this article, the reason why these high heating rates are necessary to exhibit the higher catalytic activity into formaldehyde will be discussed based on the structural changes in SMA during heating the catalysts to 873 K.     

Comparison of two-dimensional periodic arrays of convex and concave nanostructures for efficient SERS templates

We describe the optical power enhancement on the surface of the 2D (two-dimensional) periodic arrays of convex and concave gold nanostructures for comparing the characteristics of the nanostructures for surface-enhanced Raman spectroscopy (SERS) templates. The optical power enhancement is due to the surface plasmon polaritons, which is calculated by the Finite-Difference Time-Domain (FDTD) method at commercially-available 532 nm pump light. A periodic array of closely-packed gold particles is defined as convex nanostructure, while a periodic array of hemispherical holes, or voids, on gold substrate is defined as concave nanostructure. The peak power enhancement factor, the average power enhancement factor and the activity rate of each structure were compared. The convex nanostructures show a strong enhancement factor in localized hotspots, while the concave nanostructures show not only the peak power enhancement factor comparable to that of convex nanostructures, but also higher spatially-averaged power enhancement factors and activity rates than those observed on the convex nanostructures, meaning that the highly enhanced near-field zone distributes densely on the substrate. We also revealed the dependence of the void diameter on the inter-void distance for the power enhancement in the concave nanostructures system, providing a guideline for the fabrication of the efficient SERS template, which shows a strong power enhancement factor with a high area density.     

Correlation between shapes of Shockley stacking faults and structures of basal plane dislocations in 4H-SiC epilayers

Abstract

Shockley-type stacking faults expanded in 4H–SiC epilayers induced by ultraviolet illumination were investigated using a photoluminescence imaging method, a photoluminescence mapping method and X-ray topography. After ultraviolet illumination, more than 30 patterns of Shockley-type stacking faults which expanded from perfect basal plane dislocations were observed by photoluminescence imaging. The initial basal plane dislocations were crystallographically classified, and individual shapes of expanded Shockley-type stacking faults were predicted. The correspondence between the predicted shapes and observed ones was discussed.     

Theoretical study on keto–enol tautomerisation of glutarimide for exploration of the isomerisation reaction pathway of glutamic acid in proteins using density functional theory

ABSTRACT

In order to elucidate the reason why glutamic acid residues have lesser racemisation reactivity than asparaginic acid, we investigated the racemisation energy barrier of piperidinedione, which is the presumed intermediate of the isomerisation reaction of L-Glu to D-Glu, by density functional theory calculations. In two-water-molecule-assisted racemisation, the activation barrier for keto–enol isomerisation was 28.1 kcal/mol. The result showed that the activation barrier for the racemisation of glutamic acid residues was not different from that for the racemisation of aspartic acid residues. Thus, glutamic acid residues can possibly cause the racemisation reaction if the cyclic intermediate stably exists.     

Noncommutative deformation of instantons

We study instanton solutions on noncommutative Euclidean 4-space which are deformations of instanton solutions on commutative Euclidean 4-space. We show that the instanton numbers of these noncommutative instanton solutions coincide with the commutative solutions and conjecture that the instanton number in R⁴${\mathbb{R}}^4$ is preserved for general noncommutative deformations. We also study noncommutative deformation of instanton solutions on a T⁴$T^4$ with twisted boundary conditions.     

Synthesis, reaction and structure of a highly light-stable silver(I) cluster with an Ag4S4N4 core having a tridentate 4N-morpholyl 2-acetylpyridine thiosemicarbazone ligand: use of water-soluble silver(I) carboxylates as a silver(I) source

A novel neutral tetrameric silver(I) cluster [Ag(mtsc)](4) was obtained from reactions of a tridentate (4)N-morpholyl 2-acetylpyridine thiosemicarbazone ligand (N'-[1-(2-pyridyl)ethylidene] morpholine-4-carbothiohydrazide, Hmtsc) and silver(I) sources containing Ag-O bonds (Ag(2)O, Ag(OAc), silver(I) 2-pyrrolidone-5-carboxylate (infinity){[Ag(Hpyrrld)](2)}, silver(I) 5-oxo-2-tetrahydrofurancarboxylate (infinity){[Ag(othf)](2)}, and silver(I) complexes with camphanic acid (infinity){[Ag(ca)]} and (infinity){[Ag(ca)(Hca)]}). The cluster was characterized by elemental analysis, TG/DTA, FTIR and single-crystal X-ray analysis in the solid state. The solution properties of the complexes were investigated using solution molecular weight measurement, ESI-MS and solution ((1)H, (13)C and (31)P) NMR spectroscopy. The obtained cluster is a novel example of a light-stable Ag(I) cluster with a tridentate thiosemicarbazone ligand and the second report of a crystal structure of a thiosemicarbazone silver(I) complex. The reaction of the tetramer with a large excess of PPh(3) gave dimeric complexes, namely, [Ag(micro(S)-mtsc)(PPh(3))](2) and [(PPh(3))(2)Ag(micro(S)-mtsc)(2)Ag]. The chloroform solution of the tetrameric complex showed modest and effective activities against selected bacteria (Bacillus subtilis, Staphylococcus aureus and Pseudomonas aeruginosa) and yeasts (Candida albicans and Saccharomyces cerevisiae), respectively, but it did not inhibit the growth of any selected microorganisms in a water-suspension system.     

Novel synthesis of macroporous poly(N-isopropylacrylamide) hydrogels using oil-in-water emulsions

Porous N-isopropylacrylamide (NIPA) hydrogels having a unique structure, that is, spherelike cavities distributed randomly and a homogeneous network in the gel phase, were successfully synthesized by means of an emulsion templating method; this method involves the synthesis of NIPA gels in an oil-in-water (O/W) emulsion by free radical copolymerization with a cross-linker, followed by washing (removal) of the dispersed oil as a pore template (porogen). The synthesis conditions, O/W volume ratio, amount of added surfactant, and monomer concentration affect the internal pore structure, equilibrium swelling, and swelling/shrinking kinetics. A porous hydrogel swollen at 10 degrees C has a pore diameter distribution in the range of 1-40 microm, which was observed with a scanning electron microscope. Scanning electron micrographs and swelling degree reveal that the pore size and porosity can be adjusted by varying the O/W volume ratios and surfactant amounts. The porous hydrogels show very rapid swelling/shrinking in accordance with the temperature swing. The fast response is attributed to the convection flow of water through the macropores. In addition to a faster response gel, the emulsion templating method can yield potentially intelligent gels in which the pores function as spaces for reaction, separation, and storage.     

Burning velocity measurement of HFC-41, HFC-152, and HFC-161 by the spherical-vessel method

The burning velocities of fluoromethane (HFC-41), 1,2-difluoroethane (HFC-152), fluoroethane (HFC-161) and ethane were measured by the spherical-vessel (SV) method at room temperature and at initial pressures of 80-107 kPa over a wide range of HFC/air equivalence ratios (?). The burning velocities were determined from the measured pressure increases by application of a spherical flame model. Schlieren photography was used to directly observe flame propagation behavior in a cylindrical vessel equipped with optical windows. The time evolution of the flame radii derived from the pressure increases agreed with the time evolution observed with the Schlieren technique. The maximum burning velocities of HFC-41, HFC-152, HFC-161 and ethane were 28.3 cm s⁻¹ at ? = 1.01, 30.1 cm s⁻¹ at ? = 1.07, 38.3 cm s⁻¹ at ? = 1.07 and 40.9 cm s⁻¹ at ? = 1.05, respectively. The maximum burning velocities for the HFCs, including previously reported C₁ and C₂ fluoroalkanes, decreased with increasing F-substitution rate (the ratio of the number of F atoms to the sum of the number of H and F atoms). The concentrations of chemical species in the flames were investigated by means of an equilibrium calculation, and the results suggested that the burning velocity was correlated with the concentrations of H and OH radicals that were not deactivated by F radicals in the flame. The results also suggested that the burning velocities were linearly related to the heats of combustion of the C₁ and C₂ fluoroalkanes.