Helena Kubicka

The specific activity of technetium, rhenium, ruthenium, platinum, and palladium in catalytic reactions of benzene with hydrogen

Abstract The specific activities of technetium, rhenium, ruthenium, platinum, and palladium catalysts supported on silica and γ-alumina at a concentration of 1% have been studied for the reactions of benzene with hydrogen in the temperature range of 100–235 ° by the microreactor chromatographic pulse method. The surface areas of the metals were determined by selective hydrogen chemisorption at 20 ° and by the X-ray line-broadening methods. The measurements on ruthenium, platinum, and rhenium powders of known surface areas were applied to determine the metal site areas effectively occupied by one hydrogen atom. Both technetium and rhenium reveal a catalytic activity in hydrogenation of benzene to cyclohexane. At sufficiently high temperatures, both metals, like ruthenium, are also catalysts in benzene hydrogenolysis, resulting in aliphatic C 1 C 6 hydrocarbons. The specific activities of metals for hydrogenation and hydrogenolysis decrease in the order: Ru > Pt > Tc ≈ Pd > Re and Ru > Tc > Re, respectively. The apparent activation energies are 7–11 kcal/mole for hydrogenation and 29–32 kcal/mole for hydrogenolysis. Rhenium, ruthenium, platinum, and palladium supported on γ-alumina were found to be less active as compared with the same metals on silica carrier, but the maximum difference was only a nearly twofold change in specific activity. The activity and selectivity of technetium appear to be distinctly dependent on the nature of the support. In discussing the results the factors determining the catalytic activities of the metals are mainly considered e.g., the extent and strength of hydrogen adsorption, the mode of bonding of the benzene molecules, and the role of the carrier.

Hydrogen adsorption and hydrogen-oxygen titration on ruthenium powder

Hydrogen adsorption at 77–753 K, oxygen adsorption at 293 K and hydrogenoxygen titration at 293–673 K were investigated on Ru powder of known surface area. The kinds of hydrogen adsorbed, stoichiometry of oxygen chemisorption and the relevance of the data in determining metal dispersion are discussed.AbstractАдсорбция водорода при 77–753°K, адсорбция кислорода при 293°K и водородно-кислородное титрование были исследованы на порошке Ru с известной величиной поверхности. Обсуждаются виды адсорбированного водорода, стехиометрия хемисорбированного кислорода и применение этих данных для определения дисперсии металла.

Influence of oxidation-reduction treatment on dispersion of rhenium supported on γ-Al2O3

Abstract The effect of oxidation-reduction treatment on the dispersion and reducibility of Re γ- Al 2 O 3 catalysts (1.04 and 10.4 wt% Re) was studied by hydrogen chemisorption, transmission electron microscopy, electron diffraction, electron spin resonance and X-ray diffraction. It was found that oxidation at room temperature or at 673 K causes a significant (two- or three-fold) increase of Re dispersion in the catalysts reduced at 823 K. Two different mechanisms of redispersion of Re particles are proposed and discussed depending on the oxidation treatment applied. Reducibility of Re in the oxidised catalysts was found to be dependent on Re content and on the pretreatment procedure.

Chemisorption of hydrogen and oxygen on γ-alumina-supported rhenium: Part 1. Chemisorption of hydrogen

Abstract The chemisorption of hydrogen on γ-alumina-supported rhenium (10.4 wt.% and 1.04 wt.%) has been investigated gravimetrically, using a Cahn RG (HV) electrobalance, with respect to time (within 300 min), pressure (50–250 Torr, 1 Torr = 133.3 N m −2 ) and temperature (20–550°C). Some results are compared with earlier data obtained volumetrically on rhenium powder. The chemisorption of hydrogen on supported rhenium was found to be similar to that on rhenium powder and is, in part, slow, thermally activated and, at each temperature in the applied range, partially or completely reversible. The applicability of hydrogen chemisorption, under properly chosen conditions, for the determination of the surface area and dispersion of supported rhenium is indicated and the dispersion data resulting from that determination are given.

Hydrogen adsorption and hydrogen-oxygen titration on γ-alumina supported ruthenium

Hydrogen adsorption at 293–823 K, oxygen adsorption at 293 K and hydrogenoxygen titration at 293–523 K have been investigated on a 0.84% Ru/γ-Al2O3 catalyst. After correcting for adsorption on the support, the results have been found to be similar to those established earlier on Ru powder.AbstractАдсорбция водорода при 293–823° К, адсорбция кислорода при 293° К и водородно-кислородное титрование при 293–523° К были исследованы на катализаторе Ru/γ-Al2O3 (содержание Ru 0,84%). После внесения поправки на адсорбцию на носителе, результаты оказались подобными найденным ранее на порошках Ru.

Chemisorption of hydrogen and oxygen on γ-alumina-supported rhenium: Part II. Chemisorption of oxygen and hydrogen-oxygen titration

Abstract The chemisorption of oxygen and hydrogen-oxygen titration on γ-alumina-supported rhenium (10.4 wt.% and 1.04 wt.%) have been investigated gravimetrically using a Cahn RG (HV) electrobalance with respect to time (within 300 h), pressure (50–150 Torr or 50–250 Torr, 1 Torr = 133.3 N m −2 ) and temperature (20–400°C or 20–550°C). The chemisorption of oxygen was found to be slow and occurred on the surface, as well as in the volume of the rhenium. The reaction of hydrogen with surface oxygen or volume oxygen is slow or very slow and occurs only at properly enhanced temperatures. The catalyst of lower rhenium content is more resistant to oxidation and to reduction by hydrogen, indicating a strong metal-support interaction. Because of the low rate and the volume processes, chemisorption of oxygen and hydrogen-oxygen titration are considered unsuitable methods for estimating the surface area and dispersion of rhenium in the applied temperature ranges.

The dispersity of γ-alumina supported rhenium from hydrogen pulse chemisorption

The applicability of hydrogen chemisorption in a pulse chromatographic system for determining the dispersity of γ-alumina supported rhenium catalysts (10.4 wt.% and 1.04 wt.%) preheated in hydrogen at 550–800 °C is shown.AbstractПредставлена возможность использования хемосорбции водорода в импульсных хромтографических системах для определения дисперсности рениевых катализаторов, нанесенных на γ-окись алюминия (10,4 вес.% и 1,04 вес.%), и нагретых в водороде при 550–800°C.

Specific activity of ruthenium for hydrogenation and hydrogenolysis of benzene in relation to metal dispersity

The specific activity Vsp of ruthenium supported on γ-alumina (0.084–0.84 wt.%, average particle size 1=1–7 nm) has been investigated for hydrogenation and hydrogenolysis of benzene at 80–320°C and compared with that of Ru powder of 1>1400 nm. A decrease of Vsp with increasing Ru dispersity was found for both reactions, the decrease having been more pronounced for hydrogenolysis. The effect is considered to be due mainly to an influence of dispersity of supported metal on the mode and extent of benze chemisorption.AbstractСпецифическая активность (VSp) рутения, нанесенного на γ-окнсь алюминия (0,084–0,84 вес.%, средний размер частиц 1=1–7 нм), была исседована в гидрировании и гидрогенолие бензола при температуре 80–320°C и сравнива-лись со специфической активностью порошков рутения 1>1400 нм. Уменьшение VSp с увеличением дисперсии рутения было обнаружено для обеих реакций, причем наиболее сильно оно проявлялось гидрогенолизе. Этот эффект, в основ-ном, вызван влиянием дисперсности нанесенного металла на тип и степень хемо-соробции бензола.

The magnetic susceptibility of dispersed palladium

The magnetic susceptibility of palladium black of controlled purity with the average, roentgenographically determined, crystallite size of 50–450 A and surface area of 44.0–5.8 m 2 /g, was investigated at temperatures of 85–290°K. With increasing dispersion of palladium a decrease of paramagnetism, as compared with the massive metal, was found. The results are tentatively associated with occurrence of atomlike electronic states in the highly dispersed metal.

Specific activity of γ-Al2O3 supported rhenium for hydrogenation and hydrogenolysis of benzene in relation to metal concentration and dispersity

A negative influence of low concentration and of high dispersity of γ-Al2O3 supported rhenium (1.04 wt.% and 10.4 wt.% l=1.5–7.1 nm) on its specific activity for hydrogenation and hydrogenolysis of benzene at 365–573 K is described.AbstractОписывают отрицательное влияние низкой концентрации и высокой дисперсности рения, нанесенного на γ-Al2O3 (1,04 вес.% и 10,4 вес.%, l=1,5–7,1 нм), на его специфическую активностя в гидрогенизации и гидрогенолизе бензола при 363–573 К.