Search

In situ and operando diffuse reflectance FT-IR (DRIFTS) studies are often carried out over samples that may undergo changes in optical properties due to stronger absorptivity (darkening), for instance when coking or being reduced. The variation of IR optical pathlength of two Fe and Co-based Fischer-Tropsch catalysts treated at different temperatures was investigated through the use of an internal standard CaCO 3 that was physically mixed with the catalyst. The CaCO 3 overtone band at 1795 cm-1 was used, exhibiting an integral molar absorption coefficient ε = 2.68 × 105 cm mol-1. The IR penetration depth was negligible over the iron oxide sample once reduced above 400 °C, due to the formation of a strongly absorbing material. A reduction of the cobalt sample up to 350 °C revealed large changes of optical pathlength (dropping four-fold from 66 to 16 µm), likely related to the onset of cobalt oxide deep reduction. These data indicate that changes in optical pathlength should be considered when attempting quantitative DRIFTS analyses and that mixing a small concentration of CaCO 3 , e.g. 2 wt%, is a suitable way of doing so. [Display omitted] • Optical pathlengths may vary greatly during DRIFTS analyses. • Using an internal standard such as CaCO 3 can easily solve this limitation. • Iron oxide sample becomes too dark for DRIFTS upon reduction. [ABSTRACT FROM AUTHOR]

Abstract: Following the development of a high-throughput (HT) methodology for the evaluation of diesel soot oxidation catalysts in a 16 parallel channels reactor, a library of over 60 catalysts was tested under optimized conditions. The catalyst compositions were chosen to include solids which specific properties like oxygen storage capacity, oxygen mobility and ionic conductivity. The key parameters for high activity appear related to the presence of active and mobile surface oxygen species, and to an appropriate catalyst particle size in order to favour the number of contacts with the soot. In contrast, high oxygen storage capacity and bulk oxygen ion mobility do not appear as relevant properties for high catalytic activity. Nine new formulations were found to perform better than the reference catalyst “high surface area (HSA) ceria” (Rhodia). [Copyright &y& Elsevier]

Abstract: Ceria-based catalysts have been assessed for internal methane reforming at low temperature (400–600°C) in Solid Oxide Fuel Cell (SOFC). A combinatorial library of 15 metal (Cu, Pt, Ni) supported ceria was prepared using wet impregnation method. The ceria-based oxides are undoped or doped with metal transition (Zr) or by rare earth (Gd or Pr). The effect of the metal, the dopant and the surface area on the catalytic performances was investigated in high-throughput manner using a 16-parallel reactor. The catalysts were assessed in two different conditions, (i) in CH4 rich condition and (ii) in model reformate condition. Catalytic performances are very metal depending. In dry conditions, Cu-based catalysts do not produce H2 whereas Ni-catalysts are very active despite low carbon balance. However, when water and CO2 are added in the feed, the nature of the ceria plays an important role in the catalytic performances. At low temperature (T <550°C), most of Ni/ceria catalysts are not active under reformate conditions at low temperature while Pt catalysts appear more robust with respect to the conditions. From unsteady state parallel studies, we suggest that surface hydroxyl on ceria are the active species. [ABSTRACT FROM AUTHOR]

Abstract: A methodology for the evaluation of diesel soot oxidation catalysts by high-throughput (HT) screening was developed. The optimal experimental conditions (soot amount, catalyst/soot ratio, type of contact, composition and flow rate of gas reactants) ensuring a reliable and reproducible detection of light-off temperatures in a 16 parallel channels reactor were set up. The temperature profile measured in the catalyst/soot bed under TPO conditions when the exothermic combustion of soot takes place was shown to provide an accurate measurement of the ignition. Its reproducibility and relevance were checked. The results obtained with a reference noble metal free catalyst (La0.8Cr0.8Li0.2O3 perovskite) agree very well with literature data. Qualitative mechanistic features could be derived from these experiments, stressing the likely limiting step of oxygen transfer from catalyst surface to soot particulates to ignite the soot combustion. Ceria material was shown to be more appropriate than perovskite one. From an HT screening of a large diverse library (over 100 mixed oxides catalysts) under optimized conditions, about 10 new formulations were found to perform better than selected noble metal free reference materials. [Copyright &y& Elsevier]