Wyniki wyszukiwania - Biblioteka Nauki

1

Catalytic Transfer Hydrogenation of Cycloalkanones on MgO. Vapour and Liquid Phase Modes of Reaction

100%

Gliński M.

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2009

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tom Vol. 83, nr 2

187-194

EN

The reactivity of a series of cycloalkanones of the general formula (CH2)nCO, where n = 4, 5, 6, 7, 11 and 14 in the transfer hydrogenation reaction over magnesium oxide as the catalyst, either in vapour or liquid phase (VP or LP) has been studied. In the VP mode of reaction the activity of MgO treated with triethylamine, water, phenol or benzoic acid in the reduction of cyclopentanone by propan-2-ol has been determined. A strongly diminished or residual activity of MgO has been observed after the catalyst's treatment with phenol or benzoic acid, respectively. The occurence of side reactions of cyclopentanone in the LP mode of reaction resulted in high conversions of the ketone (up to 91%), very low yields of cyclopentanol (I) (be low 6%) and very high yields of 2-cyclo pentylidene-cyclopentanone (II) (greater than 80%).

2

Infrared spectroscopic study of magnesium oxide catalysts doped with sodium ions

100%

Ignaczak W. , Jóżwiak W. , Szubiakiewicz E. , Paryjczak T.

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1999

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tom vol. 73 nr 4

645-654

EN

Infrared results concerning the surface species in MgO catalysts doped with Na+ ions are presented. Different surface carbonate structures and hydroxyls groups have been found. It was assumed that created carbonate compounds could be involved in decreasing of MgO specific surface area. Sodium carbonate and unidentate carbonate structures may cause elimination and blockage of low coordination sites of MgO surface, being responsible both for hydrogen detachment from CH4 molecules and for oxidation of methyl radicals to carbon oxides - the undesired reactions of oxidative coupling of methane (OCM). It was observed that increasing temperature led to decomposition of surface bicarbonate and unidentate carbonate structures. Some of them are being reconverted to more stable bicarbonate structures. Carbon dioxide and water desorptions result in gradual restoration of low coordinated sites of MgO, corresponding to high selectivity to C2 hydrocarbon formation. Sodium ions may also cause structural changes in MgO lattice. The catalysts were active and selective above 950 K for C2 hydrocarbon formation, although sodium carbonate is sufficiently stable under the conditions of the OCM process.

3

Dye-sensitized solar cells based on sno2 nanorod and surface treatment with MG(II) film

75%

Bai J. , Murakami K.

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2009

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tom Vol. 3, No. 4

69-71

EN

Homocentrically grown SnO2 nanorods were synthesized by a hydrothermal method, whose diameter and length are around 20 nm and 100-200 nm, respectively. The photovoltaic properties of dye-sensitized SnO and MgO-treated SnO2 films were investigated. A light-to-electricity conversion yield of 0.8% was achieved by applying the nanorods as a thin film layer for the dye-sensitized solar cells. Treatment with MgO on SnO2 surface improves the photovoltage, fill factor and cell efficiency owing to preventing a recombination of the electrons injected into SnO with acceptors in the electrolyte.

4

Wpływ wybranych dodatków na hydratację tlenku magnezu

75%

Wojsa J.

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2009

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tom T. 61, nr 4

273-277

PL

Przedstawiono znaczenie hydratacji w technologii i w wybranych obszarach stosowania materiałów zasadowych. Zaprezentowano podstawowe dane dotyczące statyki i kinetyki reakcji, metody przeciwdziałania hydratacji tlenku magnezu oraz najczęściej stosowane sposoby ilościowego opisu jej efektów. Eksperymentalnie potwierdzono chemiczną inertność spineli MgAI2O4 i MgCr2O4 w warunkach hydratacji bezciśnieniowej. Zbadano wpływ czterech glikoli na hydratację MgO stwierdzając, że ich skuteczność jako inhibitorów hydratacji rośnie w sekwencji od glikolu mono-etylenowego do propylenowego. Przedstawiono wpływ soli dwusodowej EDTA na hydratację MgO oraz zweryfikowano dane literaturowe odnośnie sposobu ograniczania hydratacji poprzez wprowadzenie silikonu. Wyniki nie potwierdziły oczekiwań. Wykazano, że wolny tlenek magnezu w koklinkierze MgO-SnO2 nie ulega hydratacji, co stanowi pewną nowość poznawczą i technologiczną. Zbadano wpływ pH wodnych roztworów na hydratację MgO i uzyskano wyniki pozostające w dobrej zgodności z wynikającymi z teorii. Stwierdzono, że zmiany pH roztworów wydają się być skutecznym sposobem zwiększania stopnia hydratacji, a efektu jej ograniczania należy raczej oczekiwać wprowadzając wybrane substancje organiczne adsorbowane na powierzchni ziaren MgO, z uwzględnieniem specyfiki danej technologii.

EN

The importance of hydration in technology and in selected application areas of basic materials was shown. The thermodynamic and kinetic data of the reaction were presented. Methods of counteracting the hydration of free magnesium oxide in basic materials and the most frequently applied methods of quantitative evaluation of the effects of MgO hydration were discussed. Basing on the investigations, the chemical inertness of MgAI2O4 and MgCr2O4 spinels in the non-pressure hydration conditions was proved. The effect of four glycols on MgO hydration was analysed and it has been proved, that intensity of the reaction decreased in sequence from mono-ethylene to propylene glycol. The effect of disodium salt of EDTA on MgO hydration was described. The literature reports were experimentally verified with a negative result, regarding the limitation of MgO hydration by the introduction of silicon. The chemical inertness of free MgO in the MgO-SnO2 coclinker nas been proved, contrary to the well known magnesite-chromite materials. The effect of pH of the electrolyte water solutions on MgO hydration was explored and the results seemed to be in a good accordance with theoretical expectations. It was concluded, that the solution pH change seems to be an effective way for increasing the hydration degree, while the opposite effect should be sought through adsorption of selected organic substances, taking into consideration a specific character of the given technology.

5

Oxygen adsorption on magnesium oxide

51%

Duński H. , Jóźwiak. W.K.

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1998

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tom Z. 46

103-107

EN

The low temperature range adsorption of oxygen on the surface of magnesium oxide was investigated. The temperature-vacuum treatment of MgO above 800K resulted in the appearance of the low coordinated surface magnesium ions, most likely responsible for the relatively strong oxygen adsorption effects.

PL

Przeprowadzono badania niskotemperaturowej adsorpcji tlenu na powierzchni tlenku magnezu stosując metody TPD i EPR. Wysokotemperaturowa kalcynacja (powyżej 800K) MgO w próżni powoduje odsłonięcie niskoskoordynowanych jonów magnezu na powierzchni tlenku odpowiedzialnych za relatywnie silne efekty adsorpcji tlenu.