Peter William Ash

X-Ray Absorption Spectroscopic Studies of Platinum Speciation in Fresh and Road Aged Light-Duty Diesel Vehicle Emission Control Catalysts

Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK; and Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, UK *Email: g.sankar@ucl.ac.uk The species present in a variety of fresh and road aged light-duty diesel catalysts were determined by platinum L3 edge X-ray absorption spectroscopy (XAS). It was found that it is not suffi cient to use the analysis of X-ray absorption near edge structure (XANES) alone to determine the nature of species present in fresh and road aged catalysts. Detailed analysis of the extended X-ray absorption fi ne structure (EXAFS) revealed the presence of a mixture of oxidic and metallic species in the fresh catalysts. Metallic components were predominantly found in the road aged catalysts. The present study did not fi nd any chloroplatinate species in the systems investigated.

Local structure and speciation of platinum in fresh and road-aged North American sourced vehicle emissions catalysts: an X-ray absorption spectroscopic study.

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.

Post-Mortem investigation of Fischer Tropsch catalysts using cryo- transmission electron microscopy

Co/Al2O3 catalysts are widely used in the Fischer-Tropsch, gas to liquids (GTL), catalytic reaction where syngas (CO2 and H2) is converted into higher hydrocarbon wax products. One important use of the wax product is through cracking to produce clean diesel fuel. In most production routes the catalyst is initially in the form of highly dispersed Co-oxide particles on a high surface area gamma alumina with up to 1 wt% addition of a precious metal promoter. The catalyst can then be reduced to its active state in-situ in the FT reactor or supplied in pre-reduced form. In the case of the prereduced catalyst the material is encapsulated in a wax product to prevent re-oxidation of the cobalt. Post reaction the catalyst is suspended in the wax product of the FT reaction. It is of paramount importance to analyse the initial state and the final state of a catalyst in order to understand how the reaction has progressed. Any pre or post-reactor analysis therefore needs to deal with the wax but leave the catalyst unchanged. However, the dewaxing procedures traditionally applied to the catalyst, (Soxhlet extraction and calcination at 350°C) before examination, not only partially oxidize the Co but also cause some changes in the microstructure. Consequently, the combination of Cryoelectron microscopy and cryo-microtomy offer a straightforward, but unique, route to analyse the catalyst within its original wax environment.