Electrochemical characterization and regeneration of sulfur poisoned Pt catalysts in aqueous media

Understanding the poisoning and recovery of precious metal catalysts is greatly relevant for the chemical industry dealing with the synthesis of organic compounds. For example, hydrogenation reactions typically use platinum catalysts and sulfuric acid media, leading to poisoning by sulfur-containing species. In this work, we have applied electrochemical methods to understand the status and recovery of Pt catalysts by studying the electro-oxidation of a family of sulfur-containing species adsorbed at several types of Pt electrodes: (i) polycrystalline Pt foil; (ii) Pt single-crystal electrodes; and (iii) Pt nanoparticles supported on Vulcan carbon. The results obtained from polycrystalline Pt electrodes and Pt nanoparticles supported on Vulcan carbon demonstrate that all sulfur-containing species with different oxidation states (2-, 3+ and 4+) lead to the poisoning of Pt active sites. X-ray photoelectron spectroscopy (XPS) analysis was employed to elucidate the chemical state of sulfur species during the recovery process. The degree of poisoning decreased with increased sulfur oxidation state, while the rate of regeneration of the Pt surfaces generally increases with the oxidation state of the sulfur species. Finally, the use of Pt single-crystal electrodes reveals the surface-structure sensitivity of the oxidation of the sulfur species. This information could be useful in designing catalysts that are less susceptible to poisoning and/or more easily regenerated. These studies demonstrate voltammetry to be a powerful method for assessing the status of platinum surfaces and for recovering catalyst activity, such that electrochemical methods could find applications as sensors in catalysis and for catalyst recovery in-situ

Electrochemical characterization and regeneration of sulfur poisoned Pt catalysts in aqueous media

Fil: Agüero, Ricardo Oscar. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina

Effect of the surface structure of gold electrodes on the coadsorption of water and anions

The potential-dependent water adsorption on gold surfaces in perchloric and sulfuric acid solutions has been studied by surface-enhanced infrared absorption spectroscopy (SEIRAS). It is found that the surface structure of the gold electrodes has a major impact on the SEIRAS spectra. When the gold films are composed of nanoparticles of 47 ± 11 nm, the SEIRAS spectra are in agreement with previous reports. However, when the size of the gold nanoparticles is decreased to 27 ± 8 nm, by depositing the gold at 1 Å/s instead of 0.1 Å/s, it is found that the SEIRAS bands associated with water molecules coordinated to coadsorbed anions are absent. The combination of both types of gold electrodes allows a detailed study of the properties of the adsorbed water molecules. It is found that water molecules coadsorbed with sulfate and perchlorate anions appear to belong to the hydration shell of the anions because (i) the intensity of the SEIRAS bands of these water molecules increase with potential in the same way as the SEIRAS bands of the adsorbed anions and (ii) the frequencies of the O–H stretch resemble those of the water molecules in the hydration shell of the anions in solutio