Kinetic and mechanistic features of carbon dioxide reforming of methane over Co–Ce/ZrO2 catalysts

Carbon dioxide reforming of methane (CDRM) is an effective route to utilize CO₂ and CH₄, the most abundant, thermodynamically stable and hazardous greenhouse gases. To overcome the economical impediments to favor CDRM's industrial applicability, its mechanistic features need to be revealed both for developing efficient catalysts and optimizing operational conditions. In this context, this work aims to obtain power-law type CDRM kinetic expressions over 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts and compare and analyze mechanistic routes to elucidate the effect of the Co:Ce ratio on kinetics. The empirical power-law type rate expressions were estimated with the reaction orders of 1.63 and 1.12 for CH₄ and 0.29 and –0.12 for CO₂ for 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts, respectively. Limited CH₄ activation and, thus, carbon formation due to low Co loading lead to accumulation of surface oxygen on ZrO₂ as redox ability of Ce becomes suppressed. This causes higher CO₂ activation barrier. The presence of H₂ in the feed slows down mechanistic steps involving CH_x. The reactions including CH₄ activation, most probably reversible direct CH₄ dissociation, are found to be rate determining.     

Observation of strain relaxation in Si1-xGex layers by optical and electrical characterisation of a Schottky junction

We have studied the effect of the strain relaxation on the band-edge alignments in a Pt/p-Si_1-xGe_x Schottky junction with x=0.14 by internal photoemission spectroscopy and current–voltage measurements. We have shown that the variations in the band-edge alignments can be observed directly by measuring the optical and electrical properties of a simple Schottky junction. The strain in the Si_1-xGe_x layer has been partially relaxed by thermal treatments at two different temperatures. The degree of relaxation and other structural changes have been determined by a high-resolution X-ray diffractometer. Both optical and electrical techniques have shown that the barrier height of the Pt/Si_0.86Ge_0.14 junction increases with the amount of relaxation in the Si_1-xGe_x layer. This shows that the valence-band edge of the Si_1-xGe_x layer moves away from the Fermi level of the Pt/Si_1-xGe_x junction. The band-edge movement results from the increase in the band gap of the Si_1-xGe_x layer after the strain relaxation. This result agrees with the theoretical predictions for the strain-induced effects on the Si_1-xGe_x band structure. Received: 18 October 2000 / Accepted: 19 December 2000 / Published online: 23 March 2001     

Optical anisotropy in GaSe

Optical anisotropy of the layer semiconductor GaSe has been studied by photoluminescence (PL) and Fourier Transform Infrared Spectroscopy (FTIR). The PL spectra are dominated by two closely positioned emission bands resulting from the free exciton and the bound exciton connected direct band edge of GaSe. Photoluminescence and transmission spectra of GaSe crystals have been measured for two cases in which the propagation vector k is perpendicular (k ⟂ c) and parallel to the c‐axis (k // c). Peak position of the PL emission band and the onset of the transmission have been found to be significantly different for these two cases. This observed anisotropy is related to anisotropic band structure and the selection rules for the optical absorption in layered GaSe. FTIR transmission spectrum is in good agreement with PL results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Copolymers of 4-thieno[3,2-b]thiophen-3-ylbenzonitrile with anthracene and biphenyl; synthesis,characterization, electronic,optical, and thermal properties

Two novel copolymers of 4-thieno[3,2-b]thiophen-3-ylbenzonitrile (TT-CN), possessing electron withdrawing cyano moiety, with anthracene (P1) and biphenyl (P2) were prepared via Suzuki coupling. Optic, electronic, and thermal properties of the copolymers were investigated through UV–Vis spectroscopy, cyclic voltammetry, gel permeation chromatography, and thermal gravimetric analysis. The polymers with anthracene and biphenyl had electronic band gaps of 2.01 and 1.90 eV, respectively. Both polymers demonstrated excellent large Stokes shifts of 101 (anthracene) and 105 nm (biphenyl) as well as very good thermal properties. As they had good optical, electronic, and thermal properties, they are promising candidates for electronic applications.     

Synthesis,structural characterization and biological activities of metal(II) complexes with Schiff bases derived from 5-bromosalicylaldehyde: Ru(II) complexes transfer hydrogenation

In this study, two novel Schiff base ligands (L¹ and L²) derived from condensation of methyl 2-amino-6-methyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate and methyl 2-amino-6-phenyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate, both starting matter with 5-bromo-salicylaldehyde, and their Zn(II) and Ni(II) metal complexes have been prepared using a molar ratio of ligand:metal as 1:1 except the Ru(II) complexes 1:0.5. The structures of the obtained ligands and their metal complexes were characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR, UV–vis, thermal analysis methods, mass spectrometry, and magnetic susceptibility measurements. Antioxidant and antiradical activity of Schiff base ligands and their metal complexes were been evaluated in vitro tests. Antioxidant activities of metal complexes generally were more effectives than free Schiff bases. 1c and 2c were used as catalysts for the transfer hydrogenation (TH) of ketones. 1c, 2c complexes were found to be efficient catalyst for transfer hydrogenation reactions.     

Synthesis of new benzothiazole derivatives bearing thiadiazole as monoamine oxidase inhibitors

Monoamine oxidases (MAO) are enzymes that catalyze the oxidative deamination of monoamines such as dopamine, noradrenaline, adrenaline, and serotonin. Recent studies have shown that numerous benzothiazole derivatives exhibit hMAO inhibitory activity in the micromolar concentration range. In this study, a novel series of benzothiazole-thiadiazole (5a-5l ) was synthesized and characterized their chemical structures by ¹H-NMR, ¹³C-NMR, and Mass spectroscopy. These compounds were evaluated as inhibitors for types A and B MAO enzymes. Compounds 5f and 5l were the most active derivatives in the series with an IC₅₀ values of 0.107 ± 0.003 and 0.128 ± 0.004, respectively. Furthermore, cytotoxicity of compounds 5f and 5l were investigated and found as non-cytotoxic.