Janina Okal

Effect of chlorine on microstructure and activity of Pd/CeO2 catalysts

The evolution of microstructure and activity in benzene hydrogenation of Pd/CeO2 catalysts, prepared from Pd chloride or Pd nitrate, upon reduction at 573–973 K has been studied by X-ray diffraction (XRD), selected-area electron diffraction (SAD), high-resolution transmission electron microscopy (HRTEM) and gas chromatography. The crucial role of chloride from the metal precursor in structural transformations of the ceria support has been established and attributed to its ability to form stable cerium oxychloride at temperatures as low as 573 K. A. rapid decline to zero of the activity of Pd/CeO2 catalysts in benzene hydrogenation was observed when the temperature of reduction was increased from 573 to 773 K. This effect could not be explained by sintering, but XRD data indicated that a metal–support reaction leading to Pd–Ce alloy formation was likely to be the cause. At higher temperature (873 K) the coverage of Pd particles by a thin overlayer (probably CeOx) was observed by HRTEM.

Palladium(0) nanoparticles encapsulated in diamine-modified glycidyl methacrylate polymer (GMA-CHDA) applied as catalyst of Suzuki–Miyaura cross-coupling reaction

Cyclohexyldiamine-modified glycidyl methacrylate polymer (GMA-CHDA) in the form of gel-type beads was used to encapsulate Pd(0) nanoparticles 4–15 nm in diameter and applied as a new, reusable catalyst for the Suzuki–Miyaura cross-coupling reaction of 2- and 4-bromotoluene with phenylboronic acid. It was found that the precatalyst preparation methodology strongly influenced its catalytic activity. The best results (100% yield of the product) were obtained when GMA-CHDA was first treated with hydrazine (reducing agent for Pd(II)) and next with PdCl2 solution. The new catalyst acts heterogeneously, and the post-reaction solution after catalyst separation is not catalytically active, suggesting that there is no leaching.

Influence of oxidation–reduction treatment on the microstructure of Co/SiO2 catalyst

Abstract Evolution of microstructure and morphology of Co particles in a Co/SiO 2 catalyst during oxidation–reduction treatment was studied by electron microscopy methods. Attention was paid to phenomena taking place on the surface of particles. The redispersion of Co particles and surface roughening were observed. Catalytic activity was tested by benzene hydrogenation.

Effect of high-temperature reduction on Co/SiO2 catalysts activity in the hydrogenation of benzene

The influence of the high reduction temperature on the activity of Co/SiO2 catalysts in benzene hydrogenation has been studied. The decrease of activity is caused by strong metal-support interaction.

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.

The influence of thermal pretreatment of Re/γ-alumina catalysts in hydrogen on their activity for hydrogenation and hydrogenolysis of benzene

The specific activity of Re/γ-alumina catalysts (10.4 and 1.04 wt% Re) preheated in hydrogen at 550–800°C for benzene hydrogenation and hydrogenolysis at 80–300°C has been found to not change or to increase with increasing pretreatment temperature, respectively. The results are discussed in relation to the metal dispersion.

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.

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.

Glycothermal synthesis as a method of obtaining high surface area supports for noble metal catalysts

Abstract The catalysts for total VOC oxidation, among others noble metals supported on various materials, are still examining and all research are going to improve their catalytic properties. It is many possibilities to enhance catalyst activity and stability, for example using as supports nanocrystalline spinel type oxides with high specific surface area. Solvothermal syntheses, with their advantages in terms of high reactivity of reactants and easy control of solution reactions, are one of the methods of obtaining catalytic materials with desired properties. This work presents the microwave-assisted (MW) glycothermal synthesis as a method of obtaining nanosized mixed metal oxides with spinel structure, on the example of zinc aluminate ZnAl 2 O 4 , used as support for Pt or Pd combustion catalysts.