Changes in surface composition of Fe-Si-Cr-K oxide alkylation catalyst: the marked role of potassium ferrites

The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite.     

Evaluation of semiconducting sensor materials on the basis of catalytic test reaction

Oxidative-reductive properties on the acid-base surfaces of the oxide compositions Sn-Ce-Rh-O and Zr-Mg-Y-O, active as catalysts in the ketonization of secondary alcohols were determined based on the isopropanol conversion selectivity. The kinetics of isopropanol conversion was measured in the oxygen-free atmosphere. Activation energies for both directions of conversion (dehydration to propylene and dehydrogenation to acetone) were calculated. The results were compared with the kinetics over SnO₂ and ZrO₂. Both oxide compositions, Sn-Ce-Rh-O and Zr-Mg-Y-O are oxidative-reductive catalysts containing Lewis acid centers.     

Temperature and composition dependence of the energy band gap of Pb1−x Mn x S solid solution

Photovoltaicp-n junctions inn-type Pb_1–xMn _x Sx0.04, have been made by sulphur diffusion. Current-voltage and resistance-voltage characteristics have been examined at various temperatures. The spectral responses of the diodes have been measured within the temperature range from 5 to 300 K at a zero bias. From these measurements the energy band gap of Pb_1–x Mn _x S solid solution has been determined as a function of temperature and manganese content. A phenomenological expression describing the variation of the energy gap of Pb_1–x Mn _x S with temperature and alloy composition has been proposed.     

Metameric esters ketonization in the vapor phase over solid catalyst

Ketonization of metameric esters n-hexyl acetate and ethyl n-hexanoate was carried out in the vapor phase over Sn-Ce-Rh-O catalyst at 370°C and at 1 and 3 h^-1 load. In both cases the main products were dimethyl ketone, dipentyl ketone and methyl pentyl ketone; however, the compositions and ratios of the products obtained from both esters were different. The transformation pathways of both esters were inferred based on the quantitative differences in the composition of the products. The ratios of the particular compounds obtained during transformation of both esters indicate that the reactions proceeded simultaneously - through -ketoesters with partial thermal decomposition of esters and secondary condensation of the formed aldehydes. Also the way of creation of ketones resulting from secondary condensation was proposed.     

Catalytic Preparation of Non-Symmetrical Ketones in the Gas Phase Over Iron Oxide

The catalytic conversion of esters and mixtures of alcohols and aldehydes in the gas phase over iron oxide has been studied. The method allows for effective synthesis of non-symmetrical ketones.     

Changes in surface composition of Fe-Si-Cr-K oxide alkylation catalyst: the marked role of potassium ferrites

The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite.     

ZnFe2O4 as a new catalyst in theC-methylation of phenol

This paper reports the investigation ofC-alkylation of phenol with methanol over zinc ferrite as a catalyst. The reactions were carried out in gas phase at atmospheric pressure in dependence of increasing temperature. The total selectivity towardsortho-cresol and 2,6-xylenol over 300°C surpassed 90%. ZnFe₂O₄ was obtained by oxidative precipitation method from solution of iron (II) sulphate and zinc sulphate at 60°C. Based on the results, the best equation describing the oxidation reaction rate was found. The obtained products have been investigated using X-ray fluorescence spectrometry and X-ray diffraction analysis.     

Evidence for pygmy and giant dipole resonances in 130Sn and 132Sn

The dipole strength distribution above the one-neutron separation energy was measured in the unstable 130Sn and the double-magic 132Sn isotopes. The results were deduced from Coulomb dissociation of secondary Sn beams with energies around 500 MeV/nucleon, produced by in-flight fission of a primary 238U beam. In addition to the giant dipole resonance, a resonancelike structure ("pygmy resonance") is observed at a lower excitation energy around 10 MeV exhausting a few percent of the isovector E1 energy-weighted sum rule. The results are discussed in the context of a predicted new dipole mode of excess neutrons oscillating out of phase with the core nucleons.     

Application of the monophase Zr-Mg-Y oxide system as catalyst for gas-phase phenol methylation

The investigation presented attempts to apply the Zr-Mg-Y oxide system as a catalyst for phenol alkylation with methanol by a gas-phase reaction. The studies were carried out in a continuous process performed at atmospheric pressure. It was indicated that the catalyst obtained is active and ortho-selective in the methylation of phenol. At 370°C, in the presence of Zr-Mg-Y oxide catalyst under the experimental conditions studied, an interesting yield of ortho-cresol (over 46% with 66.5% selectivity) was attained. Zr-Mg-Y-O catalyst was prepared by low temperature method and it was characterised by X-ray powder diffraction, scanning microscopy and nitrogen physisorption. In addition, in this reaction the catalytic specificity of Zr-Mg-O, ZrO₂, MgO and Y₂O₃ was examined.     

Catalytic properties of Sn-Ce-Rh-O in dehydrogenation and oxidative dehydrogenation reactions

A new, single-phase Sn_0.925Ce_0.07Rh_0.005O₂ gas sensitive material has up to now been used as a catalyst for the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. It was subjected to the isopropanol test, the oxidative dehydrogenation of cyclohexane test, and the cyclohexene + H₂ test. A general physico-chemical analysis was done, and it included XRD, SEM, mercury porosimetry, TPD NH₃, and IR (pyridine) spectroscopy. The tests results are compliant with the basic character of the catalyst; however, it reveals significant total acidity (0.274 mmol NH₃/g) and the presence of Lewis strong acid centers (0.126 mmol Py/g). The presence of these centers in the dehydrogenating catalysts cause the ability to catalyze both the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 1, pp. 74–80. The article was submitted by the authors in English.