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[2] viXra:2011.0201 [pdf] submitted on 2020-11-30 08:54:28
Authors: Sven Anke, Tobias Falk, Georg Bendt, Ilya Sinev, Michael Hävecker, Hendrik Antoni, Ioannis Zegkinoglou, Hyosang Jeon, Axel Knop-Gericke, Robert Schlögl, Beatriz Roldan Cuenya, Stephan Schulz, Martin Muhler
Comments: 32 Pages.
CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min-1. 2 Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2 propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies.
Category: Chemistry
[1] viXra:2011.0200 [pdf] submitted on 2020-11-30 08:52:54
Authors: Rosa M. Arán-Ais, Fabian Scholten, Sebastian Kunze, Rubén Rizo, Beatriz Roldan Cuenya
Comments: 27 Pages.
The efficient electrochemical conversion of CO2 provides a route to fuels and feedstocks. Cu catalysts are well-known to be selective to multicarbon products although the role played by the surface architecture and the presence of oxides is not fully understood. Here, we report improved efficiency towards ethanol by tuning the morphology and oxidation state of the Cu catalysts via pulsed CO2 electrolysis. We establish a correlation between the enhanced production of C2+ products (76 % ethylene, ethanol and n-propanol at -1.0 V vs RHE) and the presence of (100) terraces, Cu2O, and defects on Cu(100). We monitored the evolution of the catalyst morphology by analysis of cyclic voltammetry curves and ex situ atomic force microscopy data, while the chemical state of the surface was examined via quasi in situ X-ray photoelectron spectroscopy. We show that the continuous (re-)generation of defects and Cu(I) species synergistically favors the C-C coupling pathways.
Category: Chemistry
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