Local Structure and Speciation of Platinum in Fresh and Road-Aged North American Sourced Vehicle Emissions Catalysts: An X-ray Absorption Spectroscopic Study

Abstract

Given emerging concerns about the bioavailability and toxicity of anthropogenic platinum compounds emitted into the environment from sources including vehicle emission catalysts (VEC), the platinum species present in selected North American sourced fresh and road-aged VEC were determined by Pt and Cl X-ray absorption spectroscopy. Detailed analysis of the Extended X-ray Absorption Fine Structure at the Pt L3 and L2 edges of the solid phase catalysts revealed mainly oxidic species in the fresh catalysts and metallic components dominant in the road-aged catalysts. In addition, some bimetallic components (Pt-Ni, Pt-Pd, Pt-Rh) were observed in the road-aged catalysts from supporting Ni-, Pd-, and Rh-K edge XAS studies. These detailed analyses allow for the significant conclusion that this study did not find any evidence for the presence of chloroplatinate species in the investigated solid phase of a Three Way Catalyst or Diesel Oxidation Catalysts.

Platinum group elements study in automobile catalysts and exhaust gas samples

“…Šebek et al (2011) studied two gasoline and two diesel catalysts in new condition and after 100 000 km driven. They measured Pt in gasoline catalysts within the same range of our findings in catalyst C; an average content of 679-763 μg g −1 of Pt in gasoline catalysts reported by Šebek et al (2011) and an average content of 469 μg g −1 of Pt in Catalyst C. Ash et al (2014) also measured Pt contents in TW gasoline catalytic converters (an average content of 700-800 μg g −1 ) comparable to our findings in catalyst C. Šebek et al (2011) similarly found Pd as the most abundant element in both gasoline catalysts, even though they found Pd in contents higher than what was found in our study (relatively 4 to 5 times higher); we found an average content of 2 435, 2344 and 0.6 μg g −1 of Pd in catalysts A, B and C respectively. Spada et al (2012) also found Pd to be the most present element in a composite sample of different catalytic converters used in the United States, in a content more consistent with our findings in more recent catalysts A and B.…”

“…Rh contents measured by Šebek et al (2011) are comparable to our findings in catalysts A and B, however we found 2 to 3 times less important contents (respectively 295.4 and 271.8 μg g −1 in catalysts A and B). Rh contents in gasoline catalysts of Ash et al (2014) are also within the same range of our findings in catalysts A and B.…”

Structure of Gold–Silver Nanoparticles

“…We analyzed both the Au L3-and Ag K-edges simultaneously, using procedures described elsewhere. 28,56 Fourier transforms for the Au@Ag and Au@Ag@Au colloids, along with the best fits and selected TEM images, are shown in Figure 6, and the EXAFS are shown in Figure S6 (Supporting Information). The structural parameters for these fits are given in Table 1.…”

“…In order to determine the nature of this interaction (i.e., interfacial or alloying) and to extract the structure of the particles, we analyzed the EXAFS data of the samples. We analyzed both the Au L3- and Ag K-edges simultaneously, using procedures described elsewhere. , …”

Release of Nanoparticles in the Environment and Catalytic Converters Ageing

“…Despite the environmental benefits attributed to the TWC, some studies report the release of Pt, Pd and Rh to the environment from this device [11,12]. Moreover, the vehicle's exhaust system is considered the primary source of those pollutants in urban areas [13], including CeO 2 -ZrO 2 micro and nanoparticles (NPs) [14].…”