Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V₂O₅ loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies (²⁹Si and ⁵¹V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V₂O₅ loading and formation of cerium orthovanadate (CeVO₄) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO₄ phase at higher loadings of V₂O₅. The oxidation activity increases with vanadia loading up to 8 wt.% V₂O₅, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.     

Liquid-phase Friedel-Crafts benzoylation of benzene using CuxMn(1-x)Fe2O4 spinel catalysts

The liquid-phase Friedel-Crafts acylation of benzene using benzoyl chloride as benzoylating agent was carried out over a Cu_xMn_(1-x)Fe₂O₄(x = 0, 0.2, 0.4, 0.6, 0.8 and 1) type system. The catalytic activity has been correlated with surface acidity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of chloral hydrate metabolism in adult and neonate biological fluids after single-dose administration

A simple, rapid and sensitive electron-capture gas chromatographic method has been developed for the simultaneous determination of chloral hydrate, trichloroethanol and trichloroacetic acid in biological fluids. The described method is applicable to single-dose pharmacokinetic studies of chloral hydrate in the adult. The method also meets the important requirement of using very small sample volumes and is sufficiently sensitive and reliable for disposition studies in the neonate.     

Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2

The dissociative photoionization of CH2Br2 in a region approximately 10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH0f,298(CHBr+) < or = 300.7 +/- 1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be < or = 9.17 +/- 0.23 eV. Literature values for DeltaH0f,298(CBr+) = 362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH0f,298(CH2Br2+) is revised to be 236.4 +/- 1.5 kcal mol(-1).     

Birefringence Measurement of Rapid Structural Changes during Collagen Denatu ration

Abstract— Linear birefringence, an optical property that results from a material's structure and composition, can be used to study dynamic changes in tissue structure. Single, 200 μs-long pulses from a Ho:YAG laser emitting 2.1 μm radiation were used to induce changes in the linear birefringence of rat tail tendon. Such changes were measured on a millisecond timescale. The measured rate coefficients describing the denaturation are not predicted by previous studies of collagen denaturation induced by slower, lower-temperature heating. Two types of laser-induced collagen denaturation can be differentiated: thermal denaturation, which appears rate-limited, and thermomechanical denaturation, which is observed at higher laser radiant exposures. Neither process is described by standard Arrhenius-type kinetic models.     

Selective benzylation of toluene over tungsten promoted ceria catalysts prepared by a “pseudo-template” method

Summary High surface area ceria was prepared by a pseudo-template method and doped with tungsten and sulfate ions. The modified systems were found to catalyze the liquid phase Friedel-Crafts benzylation of toluene using benzyl chloride efficiently with high selectivity towards monoalkylated product. The catalyst systems were characterized by XRD, surface area and pore volume measurements. Acid structural properties were obtained from temperature programmed desorption of ammonia.     

NDDO MO calculations

The Roby version of the NDDO MO method has been analysed by performing extensive calculations on several molecular systems employing a minimum basis set of STO-3G functions. The effect of using uniform scale factors and those derived from theS-expansion technique, for electron repulsion integrals has also been studied. At the all-electron level, the method, with all its refinements, does not appear promising. The all-valence NDDO MO method after correction byS-expansion, however, yields results which are in good agreement withab initio results. The performance of this scheme is comparable to that of the simplifiedab initio method of Brown and Roby.     

Conformations of dimethoxymethane: matrix isolation infrared and ab initio studies

Conformations of dimethoxymethane (DMM) were studied using matrix isolation infrared spectroscopy. DMM was trapped in an argon matrix using an effusive source at 298, 388 and 430 K. Experiments were also done using a supersonic jet source to look for conformational cooling in the expansion process. As a result of these experiments, spectrally resolved infrared features of the ground and first higher energy conformer of DMM have been recorded, for the first time. The experimental studies were supported by ab initio computations performed at HF and B3LYP levels, using a 6-31++G** basis set. Computationally, four minima were identified corresponding to conformers with GG, TG, G+G- and TT structures. The computed frequencies at the B3LYP level were found to compare well with the experimental matrix isolation frequencies, leading to a definitive assignment of the infrared features of DMM, for the GG and TG conformers. At the B3LYP/6-31++G** level, the energy difference between the GG and TG conformers was computed to be 2.30 kcal mol(-1). The barrier for conformation interconversion, TG-->GG level was calculated to be 0.95 kcal mol(-1). This value is consistent with the experimental observation that the spectral features due to the TG conformer disappeared in the matrix on annealing.     

Experiments and Calculations on Photoionization and Dissociative Photoionization of CH2CO

The dissociative photoionization of molecular‐beam cooled CH₂CO in a region of ?10–20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH₂CO⁺ and of observed fragment ions CH₂⁺, CHCO⁺, HCO⁺, C₂O⁺, CO⁺, and C₂H₂⁺ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH₂CO are computed with the Gaussian‐3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C‐H bonds to form CH₂⁺ + CO and CHCO⁺ + H, respectively; at greater energies, dissociation involving H migration takes place.