Crossed-beam pulsed laser deposition in a moderate He background gas pressure was used to prepare PtAu thin films. The Pt bulk content was determined by neutron activation analysis, whereas X-ray diffraction and X-ray photoelectron spectroscopy were used to assess the bulk and the surface structure of the films, respectively. It is shown that metastable PtAu alloys with a unique fcc structure are formed over the whole composition range. The surface composition of the films closely follows the bulk content, and X-ray photoelectron spectroscopy reveals that the surface of the films is also made of a PtAu alloy. These films are stable under ambient conditions. The electrochemical properties of these films were determined by cyclic voltammetry in H 2 SO 4 electrolyte, and their reactivity toward the electrooxidation of CO and the electroreduction of O 2 was assessed. The CO stripping peak potential value increases with the Au content, indicating an increased binding energy in comparison with polycrystalline Pt. Similarly, there is a cathodic shift of the Pt oxide reduction peak for the Au-rich alloy that indicates stronger Pt-O binding energies as compared with Pt-rich alloy electrodes. At the surface, the presence of Au in close proximity to Pt atoms induces a shift of the d-band center of the Pt atoms that translates into stronger bonds with CO-and O-containing species at the surface of the samples. As far as we can tell, the surface composition and structure of the deposits are not modified following the electrochemical measurements.
The electrocatalytic hydrogenolysis of pentachlorophenol
(PCP) was carried out under galvanostatic control, in an
aqueous 1 M NaOH solution in which PCP is fully soluble,
and on particles of palladium or rhodium supported on alumina
(Pd(5%)/Al2O3 or Rh(5%)/Al2O3) and entrapped in a
reticulated vitreous carbon (RVC) electrode. On Pd/Al2O3
and at 75 °C, the conversion was complete (>99%) after 16
mol of electrons per mol of substrate (16 F mol-1) were
consumed, and phenol was the sole product formed in 98%
yield (61% current efficiency). On Rh/Al2O3 and 25 °C,
100% conversion was reached after 24 F mol-1, and
cyclohexanol was obtained in 98% yield with some 2% of
cyclohexanone (62% current efficiency). The ease of
electrocatalytic hyrogenolysis was found to increase in
the following order: PCP < 2,6-dichlorophenol <
4-chlorophenol.
The electrocatalytic hydrogenation (ECH) of phenol was carried out in aqueous media with catalytic powders. The catalytic powders were composed of palladium nanoaggregates deposited on various substrates such as Al2O3, BaSO4, and BaCO3. Composite powders are trapped (upon stirring) into a reticulated vitreous carbon (RVC) matrix, allowing a rapid in situ build-up of the electrode and alleviating the use of a binder, since the latter may have a detrimental effect on the ECH. For a given amount of noble metal (5% palladium by weight), it is observed that the ECH of phenol to cyclohexanol increases in the following order: Pd/BaCO3 < Pd/BaSO4 < Pd/Al2O3. It is deduced that the ECH rate is largely dependent on the adsorption of organic molecules on the nonmetallic substrate, and a model is considered to explain such a behavior. The ECH of phenol is also feasible at a reasonable rate with composite Pd/Al2O3 (0.25% Pd by weight) powders fabricated by physical vapor deposition because the peripheral distribution of Pd nanoaggregates is favorable towards the ECH.Key words: electrocatalytic hydrogenation (ECH) of phenol, reticulated vitreous carbon (RVC), alumina-based catalyst, agglomeration process, adlineation point, adsorption.
Pulsed laser deposition (PLD) is used to deposit pure metals (Pt and Au) and a mixture of metals (Pt–Ru) at the surface of a porous aluminum anodic oxide (AAO) substrate. In the case of Pt, thick films (> 300 nm) with pore diameters larger than 150 nm (macroporous), replicating the pore structure of the underlying AAO substrate, are obtained when PLD is performed at high (> 50 eV at–1) kinetic energy (Ek) conditions. At lower Ek conditions, the characteristic structure of the AAO membrane is not discernable in the deposited film. In that case, the substrate is entirely covered by a film, the structure of which is not different from that of a Pt film deposited on a flat Si substrate under the same conditions. AAO membranes modified by macroporous Au and Pt–Ru alloy films are also prepared, demonstrating that the concept can be applied to a wide range of materials. The mechanisms responsible for the replication of the substrate pore structure in the metallic layer are discussed. These functionally modified macroporous membranes are electroactive and this aspect has been emphasized by studying the electrocatalytic properties of Pt and Pt–Ru modified macroporous membranes for CO oxidation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.