Universiteit Leiden

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Lezing

This Week’s Discoveries | 12 March 2019

Datum
12 maart 2019
Tijd
Locatie
Oort
Niels Bohrweg 2
2333 CA Leiden
Zaal
De Sitterzaal

First lecture

Title
Gravitational waves from space: ESA’s LISA mission.

Speaker
Elena Rossi (Leiden Observatory)
Elena Maria Rossi obtained her PhD at the University of Cambridge with her thesis “Structure and energy content of gamma-ray burst jets”. She held a Chandra Fellowship at University of Colorado and a postdoctoral fellowship at the Hebrew University of Jerusalem. Currently, she is an Associate Professor at the Leiden Observatory.
Her research in theoretical astrophysics and data mining focuses on studies of phenomena around compact objects and on stellar dynamics as a tool to trace the Galactic dark matter.

Second lecture

Title
Structural Principles to Steer the Selectivity of the Electrocatalytic Reduction of Aliphatic Ketones on Platinum 

Speaker
Christoph Bondü (LIC)
Broadly speaking I conduct research on electrocatalysis. That is, how does the nature of the electrode influence an electrochemical reaction. In my current project, I address this question for electrochemical hydrogenation of ketones. Here I built an understanding of how the interaction between electrode and substrate affects the catalytic activity of the electrode. On the one side I am interested in how this interaction is influenced by the crystallographic orientation of the electrode and on the other side, I want to elucidate how it is affected by the nature of the substrate.

Abstract
I am going to present the electrochemical reduction of acetone as a model reaction for the reduction of ketones. It was shown before that acetone can be reduced to propane and 2-propanol at polycrystalline platinum [1, 2]. Our own results based on online electrochemical mass spectroscopy (OLEMS) confirm the evolution of propane during acetone reduction from 0.1 M H2SO4. However, experiments at single crystal electrodes reveal that propane formation takes place at the step sites of Pt[(n+1)(100)x(110)] type crystals. No acetone reduction proceeds at pristine Pt(100)- and Pt(111)-single crystals. However, with increasing [110]-step density the current density due to acetone reduction increases at Pt[(n-1)(111)x(110)]-type electrodes. FTIR-experiments and OLEMS-experiments reveal the selective formation of 2-propanol at Pt(110)-electrodes without concomitant hydrogen evolution. Unlike Pt(100), which undergoes rapid deactivation in the course of acetone reduction, the formation of 2-propanol at Pt(110) is not hampered by the presence of even major amounts of 2-propanol.

Computational studies reveal that the sensitivity of the product distribution can be understood by the strength with which acetone binds to the respective surface sites. Pt(111) is inactive for acetone reduction because of unfavourable adsorption thermodynamics. After the first reduction step an alcoholic intermediate (CH3(COH)CH3*) remains adsorbed. At the steps of  Pt[(n-1)(111)x(110)]-type electrodes reductive desorption of the intermediate to form 2-propanol is favourable over the cleavage of the C,O-bond, while the opposite is the case for step sites of Pt[(n+1)(100)x(110)] type electrodes. The latter, therefore, go on to form propane.

[1] B. Bänsch, T. Härtung, H. Baltruschat, J. Heitbaum, Reduction and oxidation of adsorbed acetone at platinum electrodes studied by DEMS, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 259 (1989) 207-215.

[2] X. de Hemptinne, K. Schunck, Electrochemical reduction of acetone. Electrocatalytic activity of platinized platinum, Transactions of the Faraday Society, 65 (1969) 591-597.

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