BECAS
MUSSO Florencia Antonella
congresos y reuniones científicas
Título:
Caracterización de Pd/SeO2/SiO2 empleado en oxidación de α-pineno por microscopía electrónica de transmisión (TEM)
Autor/es:
FLORENCIA MUSSO; MARÍA BELÉN FARAONI; MARÍA ALICIA VOLPE; MARÍA JULIA YAÑEZ
Lugar:
Buenos Aires
Reunión:
Congreso; 15° Congreso Interamericano de Microscopía CIASEM ? SAMIC; 2019
Resumen:
Myrtenal (3) has received a growing interest in research for its bioactive properties, and it was discovered that it exhibits a broad spectrum of biological activities [1, 2]. Allylic oxidation with selenium oxide (SeO2) is one of the most used techniques in the traditional methodology, but it has several disadvantages, such as the use of high stoichiometric ratios, product mixes, very long reaction times and generation of colloidal selenium species that are difficult to eliminate, these being very toxic to the environment [3]. The heterogenization of oxidation reactions traditionally carried out following classical organic synthesis methodology presents a high impact in the context of the Green Chemistry principles.In line with this, there are several reports regarding α-pinene (1) as a starting compound, molecular oxygen as oxidizing agent and catalysts based on supported metals, such as Pd, Pt, Fe, Ru and, Cr. However, this allylic oxidation produces verbenol (4), verbenone (5) and α-pinene epoxide (6), without the production or the desired myrtenal (Figure 1) [4 ? 6].To selectively obtain myrtenal, it is proposed to design a heterogeneous catalyst selective, active, stable with low selenium load, reusable and efficient to produce the expected aldehyde. In this work, a Pd/SeO2/SiO2 catalyst was prepared and tested for the allylic oxidation reactions of α-pinene to selectively obtain a good yield to the desired myrtenal product. To do this, we rely on the selectivity of SeO2 and the oxidative capacity of Pd. The catalyst is made up of Pd nanoparticles supported on SeO2 modified silica [7]. The Pd/SeO2/SiO2 catalyst characterization was carried out mainly by Transmission Electron Microscopy (TEM) and also by XRD, FTIR, and XPS. TEM study was performed for determining Pd particle size both over fresh and used catalyst.Catalysts observation was performed in a TEM JEOL 100CX, operated at 100 kV. Digital Micrograph software was employed for measuring particles sizes. Micrographs and histograms of both fresh and used Pd/SeO2/SiO2 catalysts are showed in Figures 2 and 3, respectively. Pd particles are clearly observed. On the contrary, is not possible to distinguish SeO2 from silica support, due to the similar electronic density of both oxides. Growth of Pd crystals is observed under reaction conditions. The average size determined were 2.9 and 3.5 nm for the fresh and used samples respectively. The increase in palladium particle size notably influences on catalytic activity and selectivity. The augmentation of palladium crystals leads to a decrease in the concentration of active sites, and concomitantly to an activity depletion [8].