Browsing by Author "Medina Cabello, Francesc"

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Insights into palladium deactivation during advanced oxidation processes
(2022) Medina Cabello, Francesc; Dafinov, Anton; Pinos Vélez, Verónica Patricia; Osegueda Chicas, Oscar; Crivoi, Dana Georgiana; Llorca, Jordi; García García, Francisco Javier; García Álvarez, Mayra
A key step in creating efficient and long-lasting catalysts is understanding their deactivation mechanism(s). On this basis, the behavior of a series of Pd/corundum materials during several hydrogen adsorption/desorption cycles was studied using temperature-programmed desorption coupled with mass spectrometry and aberration-corrected transmission electron microscopy. The materials, prepared by impregnation and by sputtering, presented uniform well-dispersed Pd nanoparticles. In addition, single atoms and small clusters of Pd were only detected in the materials prepared by impregnation. Upon exposure to hydrogen, the Pd nanoparticles smaller than 2 nm and the single atoms did not present any change, while the larger ones presented a core-shell morphology, where the core was Pd and the shell was PdHx. The results suggest that the long-term activity of the materials prepared by impregnation can be attributed solely to the presence of small clusters and single atoms of Pd.
Performance of the catalytic membrane reactors of different pore size with palladium as catalytic phase in hydrogenation and oxidation reactions
(2018) Pinos Vélez, Verónica Patricia; Medina Cabello, Francesc; Dafinov Ivanov, Anton Ivanov
The catalytic membrane reactors (CMR) were prepared using a commercial Hollow Fiber Membrane of corundum of 4 and 1400 nm and impregnated palladium. The tests performed were phenol hydrogenation, hydrogen peroxide generation to oxidize phenol by advanced oxidation processes and chromium (VI) reduction. Reactions were performed in aqueous solution, mild temperature and atmospheric pressure. For all tests, the hydrogen passed through the membrane to be activated with palladium. The test with phenol showed that in absence of oxygen, the activate hydrogen reacts with the organic matter leading to the formation of hydrogenated products; while, in the presence of oxygen, active hydrogen reacts with the oxygen to form hydrogen peroxide and subsequently hydroxyl radicals that attack the organic matter until its mineralization. Furthermore, the CMR is capable of reducing chromium VI to chromium III. The CMRs of less pore size present better performance in all reactions.