Scientific Highlights

Datum
26 March 2021
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Important elementary reactions of lignin catalytic pyrolysis revealed

To develop sustainable lignin valorization strategies, a solid understanding of the underlying reaction mechanism is critical. By detection of highly reactive and elusive intermediates, new light could be shed on one of the most basic elementary reactions in lignin catalytic fast pyrolysis.

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25 March 2021
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HERCULES SCHOOL 2021 AT PSI

During the week of March 15 – 19, we had the pleasure to welcome 20 international PhD students, PostDocs and assistant professors at PSI, taking part in the first virtual HERCULES SCHOOL on Neutrons & Synchrotron Radiation.

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24 November 2020
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Ruzicka Prize

The Ružička ​Prize 2020 goes to Dr. Patrick Hemberger (PSI) for his research on understanding the mechanisms of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysts.

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1 August 2020
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Methylbismuth: First observation of an organometallic biradical reactive intermediate

Open shell organometallic bismuth are promising agents for catalytic applications, but difficult to characterize due to their high reactivity. The simplest methylbismuth (Bi-CH3), a biradical species, was in-situ synthesized and spectroscopically characterized for the first time. Electronic and thermochemical properties could be obtained, which will guide future synthetic applications.

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26 March 2019
Operando spectroscopy techniques, including PEPICO, unravel the mechanistic origin of halogen-dependent selectivities in oxyhalogenation.

Selective Alkane Functionalization to Olefins

Light alkanes are abundantly available and cheap resources that are often burned at oil wells because of the missing infrastructure for valorization. Novel technologies are needed for their selective functionalization to use natural gas as an energy vector in the transition between the oil and the renewables era. Catalytic oxyhalogenation may unlock the transformation of cheap and abundant alkanes into commodities. When chlorine-based reactions are compared with bromine, improved selectivities above an iron catalyst arise from surface-confinement of the reaction mechanism in the case of chlorine as halogen.

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15 February 2019
Ultrafast Radical Reactions: Comic art illustrating the reactivity of electronically excited xylyl radicals. Here the meta-xylyl radicals (M) sticks out and depletes twice as fast into the vibrationally hot ground state

How the methyl group position influences the ultrafast deactivation in aromatic radicals

The resonantly stabilized xylyl radicals (C8H9•) distinctively influence the combustion chemistry and, therefore, ultimately determine the performance of combustion engines. At that, the three different isomers (methyl group in ortho, para or meta position) exhibit notable differences at elevated temperatures. We have tracked down these dynamics on a femtosecond timescale by monitoring the response to preparation of a well-defined electronic and vibrational state.

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31 October 2018
Dissociation thresholds and internal energy distributions can be measured by iPEPICO. The latter allow us to determine temperatures in dilute samples of reactive intermediates and radicals.

Radical Thermometers and Energetics

Methylperoxy radicals are crucial oxidation intermediates and could be synthesized photolytically in an exothermic reaction. Despite their vanishingly small concentration, their temperature could be measured after a few ten thousand collisions inside the reactor, which opens up the possibility of time-resolved operando temperature measurements. Also the reaction energy to yield methyl cations and oxygen could be determined with sub-kJ mol–1 precision, which firmly anchors the methylperoxy energetics to that of well-known stable species and opens up the possibility of highly accurate radical thermochemistry measurements.

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30 October 2018
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Taming Reactive Molecular Magnets

Studying organic molecular magnets is a challenge, because the high-spin diradical character of these compounds dramatically increases the reactivity and reduces the lifetime. Researchers from PSI, ETH Zurich, Wollongong and Melbourne, Australia succeeded in taming the meta-xylylene diradical and were able to study its electronic and thermochemical properties.

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1 June 2018
Methyl radicals and bromine atoms were detected in the gas phase revealing the interplay of surface-catalyzed and gas-phase reactions in the catalytic oxybromination of methane.

Tracking down radicals in methane oxybromination

Catalytic oxybromination may turn the cheap and abundant feedstock methane into the platform compounds bromomethane and dibromomethane. Yet researchers have been puzzled by the catalysis mechanism, which was speculated to involve free radical intermediates. Operando photoelectron photoion coincidence helped distinguish surface and gas-phase reaction steps and elucidated the crucial halogen-mediated C–H bond activation step, which is driven by elusive bromine and methyl radicals.

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