Effect of the carbon nanotube basicity in Pd/N-CNT catalysts on the synthesis of R-1-phenyl ethyl acetate

Catalytic activities of palladium catalysts supported on activated carbon and carbon nanotubes were investigated in the one-pot synthesis of R-1-phenylethyl acetate in combination with an immobilized lipase in toluene. Palladium catalysts on carbon nanotubes with nitrogen-containing surface groups were prepared by incipient wetness impregnation. The basic N-CNT support was synthesized by post-treating oxidized CNTs in gaseous NH3 at high temperature, prior to Pd addition. The basic character of the support was adjusted by controlling the temperature of the post-treatment step. The results showed that the desired product yield was enhanced over palladium catalysts with the lowest basicity

Citral hydrogenation over Pt loaded micro- and mesoporous supports : the interplay between steric limitations and acidity

The effect of pore morphology and acidity on the selectivity in the hydrogenation of citral was investigated on a series of bifunctional catalysts: Pt-H-SAPO-5, Pt-H-Y zeolite, and Pt-H-MCM-41. The reaction was studied in a batch reactor at 70oC with 10 bar total pressure. The highest selectivity to the unsaturated alcohols of 57% was obtained on the Pt-H-SAPO-5 catalyst at a conversion of 46%. The interplay among a monodimensional pore channel of the H-SAPO-5 support, weak Br?nsted acidity of this silicoaluminophosphate, and large platinum nanoparticles contributed to a high selectivity. The corresponding turn over frequency was 0.036 s-1. Pt-H-MCM-41 showed the highest selectivity to menthol as by product, while Pt-H-Y zeolite demonstrated the highest dehydration rate

Diffusion Measurements of Hydrocarbons in Zeolites with Pulse-Field Gradient Nuclear Magnetic Resonance Spectroscopy

Pulse field gradient NMR technique was used to determine self-diffusivity of heptane and pentadecane at room temperature for microporous catalysts, used both as powders and shaped with a binder extrudates. The results showed that diffusivities increased with increasing specific surface area, micro- and mesopore volume of the studied catalysts. The presence of Bindzil binder together with H-Beta-25 decreased hydrocarbon diffusivities. Self-diffusivities of heptane and pentadecane were smaller for extrudates than for the powder catalysts. The detailed information about mass transfer limitations is needed to further process optimization since effective diffusivity is directly correlated with self-diffusion coefficients. The estimates of the ratio of porosity and tortuosity were also determined. The diffusion measurements with relatively long observation times Delta (20 up to 1000 ms) and catalysts fully immersed in pentadecane revealed that a small portion of sites exhibits very small diffusivities in H-Beta-25-Bindzil extrudates, which is correlated with a low ratio of mesopore to micropore volumes of this material

Kinetic regularities, catalyst deactivation and reactivation

Funding text 1 The research is funded from Ministry of Education and Science of the Russian Federation Program No. 075–03–2021–287/6 (Russia). Funding text 2 XPS measurements were carried out at the Central laboratories of Tomsk Polytechnic University (Analytical Center). HRTEM was carried out at the Innovation centre for Nanomaterials and Nanotechnologies of Tomsk Polytechnic University. The ICP-OES analysis was carried out using the core facilities of “Physics and Chemical methods of analysis” of Tomsk Polytechnic University. Fundação para a Ciência e a Tecnologia for Scientific Employment Stimulus Institutional Call (CEECINST/00102/2018), UIDB/50006/2020 and UIDP/50006/2020 (LAQV), UIDB/00100/2020 and UIDP/00100/2020 (Centro de Química Estrutural).Betulin, being a pentacyclic triterpene alcohol and an extractive from birch bark, along with its oxo-derivatives, has a broad range of physiological properties of interest for synthesis of pharmaceuticals. Instead of oxidizing betulin with strong and toxic oxidizing agents the present study shows a possibility of using liquid-phase oxidation of betulin with air over supported Ag NPs catalysts as an alternative method for synthesis of its oxo-derivatives. Based on catalytic studies, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy, the evolution of the surface of nanosilver catalysts during the catalysis was demonstrated, as well as under the impact of reactant gas composition. The kinetic regularities and causes of deactivation of supported Ag NPs catalysts were revealed. An approach to the regeneration of silver catalysts was proposed. Kinetic analysis with numerical data fitting was performed resulting in an adequate description of the concentration dependencies.publishersversionpublishe

Cascade transformations of (±)-citronellal to menthol over extruded Ru-MCM-41 catalysts in a continuous reactor

Cascade transformations of (±)-citronellal in a continuous mode were investigated over a bifunctional shaped ruthenium catalyst bearing metal clusters of the size 7–13 nm. Four types of Ru/H-MCM-41 extrudates (1.5 × 10 mm) containing 30% of Bindzil-50/80 colloidal silica binder were prepared varying in metal location and metal-to-acid ratio, while the concentration of Brønsted and Lewis acid sites and textural properties of the final extrudates were comparable. Catalytic tests were performed in the trickle-bed reactor under 70 °C, 10 bar of H2, and the initial reactant concentration in cyclohexane 0.086 mol L−1 for the liquid residence time of 12.5 min. As a reactant, isopulegol, citronellol or (±)-citronellal was used. Metal location in extrudates has a significant effect on the catalytic activity and selectivity especially in terms of isopulegol isomers which content correlated with the metal-to-acid site ratio. Stereoselectivity to the desired (±)-menthol was 68–70%. The highest amount of the desired menthol, 32% yield, was obtained over extrudates where Ru was deposited on the catalytic support, i.e. with the shortest distance between the acid and metal sites, the lowest Brønsted acidity, the lowest Brønsted–Lewis acid sites ratio, the highest specific surface area and the narrowest range of the Ru particle size distribution.</p

Supported silver nanoparticles as catalysts for liquid-phase betulin oxidation

The research is funded from the Russian Science Foundation project No. 18-73-00019, Tomsk Polytechnic University Competitiveness Enhancement Program, project VIU-ISHBMT-197/2020 and Tomsk Polytechnic University State Task "Science", project FSWW-2020-0011 (Russia). This work was partially supported by Fundacao para a Ciencia e a Tecnologia, Portugal, through project UIDB/00100/2020 of the Centro de Quimica Estrutural, by national funds though FCT, under the Scientific Employment Stimulus-Institutional Call (CEECINST/00102/2018) and the Associate Laboratory for Green Chemistry-LAQV financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020).Herein, it has been shown that betulin can be transformed into its biologically active oxo-derivatives (betulone, betulinic and betulonic aldehydes) by liquid-phase oxidation over supported silver catalysts under mild conditions. In order to identify the main factors determining the catalytic behavior of nanosilver catalysts in betulin oxidation, silver was deposited on various alumina supports (γ-alumina and boehmite) using deposition–precipitation with NaOH and incipient wetness impregnation methods, followed by treatment in H2 or O2. Silver catalysts and the corresponding supports were characterized by X-ray diffraction, nitrogen physisorption, inductively coupled plasma optical emission spectroscopy, photoelectron spectroscopy and transmission electron microscopy. It was found that the support nature, preparation and treatment methods predetermine not only the average Ag nanoparticles size and their distribution, but also the selectivity of betulin oxidation, and thereby, the catalytic behavior of Ag catalysts. In fact, the support nature had the most considerable effect. Betulin conversion, depending on the support, increased in the following order: Ag/boehmite < Ag/boehmite (calcined) < Ag/γ-alumina. However, in the same order, the share of side reactions catalyzed by strong Lewis acid centers of the support also increased. Poisoning of the latter by NaOH during catalysts preparation can reduce side reactions. Additionally, it was revealed that the betulin oxidation catalyzed by nanosilver catalysts is a structure-sensitive reaction.publishersversionpublishe