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PRINCIPAL PUBLICATION AND AUTHORS

In Situ X-ray Raman scattering spectroscopy of the formation of cobalt carbides in a Co/TiO2 Fischer- Tropsch synthesis catalyst, J.G. Moya-Cancino (a), A.-P. Honkanen (b), A.M.J. van der Eerden (a), R. Oord (a), M. Monai (a), I. ten Have (a), C.J. Sahle (c), F. Meirer (a), B.M. Weckhuysen (a), F.M.F. de Groot (a), S. Huotari (b), ACS Catal. 11, 809-819 (2021); https:/doi.org/10.1021/acscatal.0c04509 (a) Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University (The Netherlands) (b) Department of Physics, University of Helsinki (Finland) (c) ESRF

REFERENCES

[1] N.E. Tsakoumis et al., Catal. Today 154, 162-182 (2010). [2] I.C. ten Have & B.M. Weckhuysen, Chem Catal. 1, 339-363 (2021).

Mercury detoxification process in animals revealed

X-ray absorption spectroscopy has been used to reveal how water birds detoxify the poisonous element mercury from their bodies, and shows that this process consumes more selenium than previously thought. The results suggest a new, possibly universal, biomineralisation mechanism.

Mercury is a global pollutant that is generated both by natural sources, such as volcanoes and forest fires, and human activities, such as gold mining and coal combustion. In aquatic and terrestrial food chains it accumulates as methylmercury, which can affect the function of animals brains and reproductive systems. Chemically reduced forms of selenium, such as selenide, have long been known to detoxify mercury, but the biochemical mechanism was unknown.

Some water birds have body mercury levels that are much higher than the toxicity threshold in humans. Tissue samples of two bird species those of giant petrels found in the Kerguelen Islands in Antarctica, and the Clark s grebe, a water bird found in the lakes and wetlands of coastal California in the US were studied via an integrative approach combining chemical analyses, high-resolution transmission electron microscopy and high energy- resolution X-ray absorption spectroscopy (HR-XANES and

EXAFS) at beamline ID26. A selenium-containing mercury species, Hg(Sec)4, containing four selenocysteine amino acids, was detected first in the liver of the Clark s grebe (Figure 89) and then in the liver, kidneys, muscles and brain of the giant petrels.

The chemical species, which forms a complex with selenoprotein P, is thought to be the main missing intermediate reaction species of the sequential demethylation reaction MeHgCys → Hg(Sec)4 → Hgx(Se,Sec)y → HgSe (Cys = cysteine; Sec = selenocysteine). This reaction helps animals survive high levels of mercury by biomineralising toxic methylmercury into non-toxic, chemically inert mercury selenide (HgSe). The molar ratio of selenium to mercury in Hg(Sec)4 is 4:1, meaning four selenium atoms are required to detoxify a single mercury atom. It is therefore generally considered that mercury is without toxicological consequences as long as there is sufficient selenium. The same biomineralisation reaction has since been identified in other species of bird and a mammal, the long-finned pilot whale [1-3], suggesting a possibly universal biomineralisation process.

The spectroscopic data enabled the quantification of the bioavailable selenium in several tissues of the birds from the concentrations of each Se-bound mercury species (Figure 90). It was found that Hg(Sec)4 severely depletes the amount of bioavailable selenium in the birds, more so than previously thought when only considering mercury

experiment (carburisation reaction). Figure 88 shows an image of the capillary reactor and XRD measurements performed at different positions in the reactor bed during 6h of carburisation reaction. A larger conversion rate was observed at the beginning of the catalyst bed of the reactor, and the conversion gradually decreased with increasing distance from the gas inlet. This finding agrees with the conversion expected for a plug flow reactor, and it represents an important factor regarding the experimental scientific methodology that must be considered for the correct evaluation and interpretation of data.

In conclusion, a novel in-situ XRS/XRD study was performed to research the formation of Co2C at relevant FTS reaction conditions. The main features of Co L2,3- edges and C K-edge for Co2C were obtained. However, there is no conclusive evidence that instable Co2C formation during the FTS reaction is related to the deactivation of the catalysts or to the increase of selectivity towards lower olefins and intermediate species during the reaction. Additionally, the gradient in the conversion of Co2C along the bed of the reactor is an important factor that must be considered when planning and executing experiments, in order to avoid misinterpretation of the data.