Atomically dispersed platinum on low index and stepped ceria surfaces: phase diagrams and stability analysis

Ab initio atomistic thermodynamics modeling demonstrated that atomically dispersed platinum species on ceria adopt a range of local coordination configurations and oxidation states that depend on the surface structure and environmental conditions.

Ultra-fine platinum species supported on niobium pentoxide for CO oxidation

Ultrafine-clustered metallic Pt species are considered to be more active than oxidized Pt single ions for CO oxidation reaction.

Application of the direct peptide reactivity assay (DPRA) to inorganic compounds: a case study of platinum species

The in chemico Direct Peptide Reactivity Assay (DPRA) was developed as a non-animal, relatively high throughput, screening tool for skin sensitization potential. Although the Adverse Outcome Pathway (AOP) for respiratory sensitization remains to be fully elucidated, it is recognized that the molecular initiation event for both skin and respiratory sensitization to low molecular weight chemicals involves haptenation with proteins. The DPRA examines the reactivity of a test compound to two model peptides (containing either cysteine or lysine) and consequently is able to screen for both skin and respiratory sensitization potential. The DPRA was primarily developed for and validated with organic compounds and assessment of the applicability of the assay to metal compounds has received only limited attention. This paper reports the successful application of the DPRA to a series of platinum compounds, including hexachloroplatinate and tetrachloroplatinate salts, which are some of the most potent chemical respiratory sensitizers known. Eleven platinum compounds were evaluated using the DPRA protocol as detailed by Lalko et al., with only minor modification. Two palladium compounds with structures similar to that of the platinum species studied and cobalt chloride were additionally tested for comparison. The hexachloroplatinate and tetrachloroplatinate salts showed exceptionally high reactivity with the cysteine peptide (EC15 values of 1.4 and 14 μM, respectively). However, for platinum compounds (e.g. hydrogen hexahydroxyplatinate and tetraammineplatinum) where clinical and epidemiological evidence indicates limited sensitization potential, the cysteine DPRA showed only minor or no reactivity (EC15 values of 24 600 and >30 000 μM, respectively). The outcomes of the lysine peptide assays were less robust and where EC15 was measurable, values were substantially higher than the corresponding results from the cysteine assay. This work supports the value of in chemico peptide reactivity as a metric for assessment of platinum sensitization potential and therefore in screening of new platinum compounds for low or absent sensitization potential. Additional studies are required to determine whether the DPRA may be successfully applied to other metals. We provide details on method modifications and precautions important to the success of the DPRA in the assessment of metal reactivity.

Water-mediated photo-induced reduction of platinum films

Platinum thin films activated ex situ by oxygen plasma become reduced by the combined effect of an intense soft X-ray photon beam and condensed water. The evolution of the electronic structure of the surface has been characterized by near-ambient-pressure photoemission and mimics the inverse two-step sequence observed in the electro-oxidation of platinum, i.e. the surface-oxidized platinum species are reduced first and then the adsorbed species desorb in a second step leading to a surface dominated by metallic platinum. The comparison with measurements performed under high-vacuum conditions suggests that the reduction process is mainly induced by the reactive species generated by the radiolysis of water. When the photon flux is decreased, then the reduction process becomes slower.

Mobility of dissolved palladium and platinum species under water-rock interaction in chloride media: modeling of PGE behavior under interaction of oceanic serpentinites with sea water derivates

To elucidate the possibility of PGE transfer by highly-salt chloride solutions, the palladium and platinum behavior was simulated in the conditions of low-temperature hydrothermal transformation of serpentinites of the oceanic crust. In dynamic water-rock experiments using columns filled with crushed ultrabasic rocks of the ocean floor (harzburgite serpentinites of mid-oceanic ridges with different degrees of carbonatization), it is established that the efficiency of palladium transfer depends on the alteration (carbonatization) degree of peridotites and under the experimental conditions is 80–100%. It is assumed that the transport of palladium occurs as a result of the formation of a strong complex compound with thiosulfate ion, which is an intermediate oxidation product in the “sulphide-sulfate” system. Platinum, hydrolyzed at approximately neutral pH and not forming compounds with thiosulfate ion, is completely retained by serpentinites, possibly due to sorption interactions with silicates. Thus, the higher mobility of palladium during the low- temperature transformation of abyssal peridotites and the dependence of the character of its distribution in the studied rocks on the processes of serpentinization and carbonatization have been confirmed.