The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

© The Author(s) 2018Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.Fonds zur Förderung der wissenschaftlichen Forschung (FWF)212921411

Rhodium-Catalyzed Methanation and Methane Steam Reforming Reactions on Rhodium-Perovskite Systems: Metal-Support Interaction

Metal-support interaction in rhodium-perovskite systems was studied using LSF (La0.6Sr0.4FeO3-[delta]) and STF (SrTi0.7Fe0.3O3-[delta]) supports to disentangle different manifestations of strong or reactive metalsupport interaction. Electron microscopy and catalytic characterization in methane steam reforming/CO2 methanation reveal that reduction in hydrogen at 673K and 873K causes different extents of Fe exsolution. Depending on the perovskite reducibility, Fe-Rh alloy particles are observed. No signs of strong metal-support interaction (i.e., encapsulation of metal particles) by reduced oxide species were observed. As reoxidation in oxygen at 873K did not fully restore the initial structures, the interaction between Rh and the perovskites manifests itself in irreversible alloy formation. Catalytic effects are the suppression of methane reactivity with increasing prereduction temperature. The results show the limits of the strong metal-support interaction concept in complex metal-oxide systems.(VLID)1371554Accepted versio

Mechanistic insights into the catalytic methanol steam reforming performance of Cu/ZrO₂ catalysts by in situ and operando studies

We assessed the catalytic properties of the Cu/ZrO2 interface in methanol and formaldehyde steam reforming (MSR and FSR) on powder catalysts by using a comparative approach with respect to the influence of the ZrO2 polymorph support structure (monoclinic (m-)ZrO2vs. tetragonal (t-)ZrO2), its synthesis routine and the choice of the precursor material on the CO2 selectivity. Our studies reveal that ZrO2 exhibits a pronounced versatility as a support material and its catalytic properties depend most strongly on its surface properties governed by its synthesis, especially by the choice of the Zr precursor. The way of combining the support with copper introduces an additional layer of complexity, but its influence on the MSR performance is limited to a modification of the conditions provided by the ZrO2 support. Exploiting the comparative approach regarding the Cu-ZrO2 catalysts in FSR and MSR – including the pure support materials – in combination with in situ Fourier transform infrared (FT-IR) spectroscopy shows that the CO observed in MSR on Cu/m-ZrO2 can be attributed to a spillover of formaldehyde to the support. Side reactions of m-ZrO2 are suppressed at lower temperatures due to its lack of highly reactive sites, resulting in a CO2-selective MSR performance. In Cu/t-ZrO2, however, the amount of CO is higher and a combination of a formaldehyde spillover to the support and a Cu-ZrO2 phase boundary yielding CO leads to the lower CO2 selectivity of these samples. An elevated number of defects and reactive Lewis acidic and Brønsted basic centers of t-ZrO2 explains this increased activity towards side reactions in contrast to Cu/m-ZrO2 catalysts

Mechanistic insights into the catalytic methanol steam reforming performance of Cu/ZrO2 catalysts by in situ and operando studies

We assessed the catalytic properties of the Cu/ZrO2 interface in methanol and formaldehyde steam reforming (MSR and FSR) on powder catalysts by using a comparative approach with respect to the influence of the ZrO2 polymorph support structure (monoclinic (m-)ZrO2 vs. tetragonal (t-)ZrO2), its synthesis routine and the choice of the precursor material on the CO2 selectivity. Our studies reveal that ZrO2 exhibits a pronounced versatility as a support material and its catalytic properties depend most strongly on its surface properties governed by its synthesis, especially by the choice of the Zr precursor. The way of combining the support with copper introduces an additional layer of complexity, but its influence on the MSR performance is limited to a modification of the conditions provided by the ZrO2 support. Exploiting the comparative approach regarding the Cu-ZrO2 catalysts in FSR and MSR – including the pure support materials – in combination with in situ Fourier transform infrared (FT-IR) spectroscopy shows that the CO observed in MSR on Cu/m-ZrO2 can be attributed to a spillover of formaldehyde to the support. Side reactions of m-ZrO2 are suppressed at lower temperatures due to its lack of highly reactive sites, resulting in a CO2-selective MSR performance. In Cu/t-ZrO2, however, the amount of CO is higher and a combination of a formaldehyde spillover to the support and a Cu-ZrO2 phase boundary yielding CO leads to the lower CO2 selectivity of these samples. An elevated number of defects and reactive Lewis acidic and Brønsted basic centers of t-ZrO2 explains this increased activity towards side reactions in contrast to Cu/m-ZrO2 catalysts

Screening Programme 2017 – AMAP Assessment Compounds

This report summarizes the findings of a screening study on the occurrence of emerging substances selected by AMAP and other related substances measured earlier. The study includes selected solvents, siloxanes, flame retardants, UV compounds, pesticides, bisphenols and other PBT compounds in effluent, ambient air, biota, and marine plastic