Ultrasound-assisted selective hydrogenation of C-5 acetylene alcohols with Lindlar catalysts

Preparation and Catalytic Hydrodechlorination Property of Nano Bimetallic Catalyst Pd–Ni/γAl2O3–SiO2

Pd–Ni bimetallic catalyst supported on a composite carrier of γAl2O3 and SiO2 was prepared by chemical precipitation methodology enhanced with an ultrasonic wave. In the present paper, the influence of dispersant, carrier, ultrasonic time and intensity on the dechlorination property of the catalysts obtained are investigated. The appearance, morphology and structure of the prepared catalysts were characterized using X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), N2 adsorption–desorption isotherm and X-ray photoelectron spectroscopy spectrometer (XPS). The chemical composition of active gradients in the catalysts was tested with inductively coupled plasma-atomic emission spectrometry (ICP-AES). The metal dispersion and mean particle size of the metallic phase of the prepared catalysts were also determined with CO chemisorption. Results indicate that a nano bimetal Pd–Ni catalyst on an average particle size of 2.45 nm with a distribution range of 1–7 nm supported on a composite carrier of γAl2O3 and SiO2 can be effectively prepared, and that the chlorine content of shellac dechlorinated with the obtained catalyst is 0.18 wt%, which is lower than that reported in the previous literature, indicating the perfect dechlorination property of the catalyst.

Selectivity of the Lindlar catalyst in alkyne semi-hydrogenation: a direct liquid-phase adsorption study

Pd catalysts contain active sites that strongly adsorb alkyne and alkene molecules. The presence of the latter, alkene sites, defines the low semi-hydrogenation selectivity.

Ultrasound-Assisted Hydrazine Reduction Method for the Preparation of Nickel Nanoparticles, Physicochemical Characterization and Catalytic Application in Suzuki-Miyaura Cross-Coupling Reaction

In the experimental work leading to this contribution, the parameters of the ultrasound treatment (temperature, output power, emission periodicity) were varied to learn about the effects of the sonication on the crystallization of Ni nanoparticles during the hydrazine reduction technique. The solids were studied in detail by X-ray diffractometry, dynamic light scattering, thermogravimetry, specific surface area, pore size analysis, temperature-programmed CO₂/NH₃ desorption and scanning electron microscopy. It was found that the thermal behaviour, specific surface area, total pore volume and the acid-base character of the solids were mainly determined by the amount of the nickel hydroxide residues. The highest total acidity was recorded over the solid under low-power (30 W) continuous ultrasonic treatment. The catalytic behaviour of the nanoparticles was tested in a Suzuki-Miyaura cross-coupling reaction over five samples prepared in the conventional as well as the ultrasonic ways. The ultrasonically prepared catalysts usually performed better, and the highest catalytic activity was measured over the nanoparticles prepared under low-power (30 W) continuous sonication.

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Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1-0.5MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.