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[3] viXra:2205.0052 [pdf] submitted on 2022-05-09 20:31:39
Authors: Uta Hejral, Janis Timoshenko, David Kordus, Mauricio Lopez Luna, Nuria J. Divins, Simon Widrinna, Ioannis Zegkinoglou, Lukas Pielsticker, Hemma Mistry, Jorge Anibal Boscoboinik, Stefanie Kuehl, Beatriz Roldan Cuenya
Comments: 41 Pages.
The hydrogenation of CO2 into high energy density fuels such as methanol, where the required H2 is obtained from renewable sources, is of utmost importance for a sustainable society. In recent years, NiGa alloys have attracted attention as promising catalyst material systems for the hydrogenation of CO2 into methanol at ambient pressures. They thus represent an energy-saving alternative to the Cu-based catalysts employed in today’s catalytic industry that require high pressures for the CO2 hydrogenation. However, the underlying reaction mechanisms for the NiGa system are still under debate. One of the challenges here is to unravel the evolution and coexistence of the different species in the heterogeneous NiGa catalyst system under activation and reaction conditions. To shed light on their evolution under H2 activation and their catalytic roles under CO2 hydrogenation working conditions on defined Ni3Ga1 and Ni5Ga3 nanoparticle (NP) catalysts, we employed a multi-probe approach. It included advanced machine learning-based analysis of operando X-ray absorption spectroscopy data combined with operando powder X-ray diffraction and near ambient pressure X-ray photoelectron spectroscopy measurements, as well as reactivity studies using bed-packed mass flow reactors. In addition, we employed atomic force microscopy and scanning transmission electron microscopy for structural characterization.
Under H2 activation at 1 bar total pressure, we conclude the formation of metallic Ni, starting for Ni3Ga1 at 300˚C, and for Ni5Ga3 at 400˚C. At higher temperatures, the formation of NiGa alloys follows. The α’-Ni3Ga1 alloy phase is predominantly formed for the Ni3Ga1 NPs, while the coexistence of α’-Ni3Ga1, δ-Ni5Ga3 and Ga2O3 phases is observed for the Ni5Ga3 NPs after the H2 activation. The formation of the Ga2O3 phase also results in the presence of excess metallic Ni. Under CO2 hydrogenation reaction conditions, Ga partially oxidizes again to form a Ga2O3-rich particle shell for both NP compositions, yet, to a larger extent for the Ni3Ga1 NPs, which, in turn, feature a higher amount of excess Ni. We reveal that metallic Ni is responsible for the high selectivity of the Ni3Ga1 NPs towards the production of methane in our catalytic tests. Contrary, the Ni5Ga3 NPs display a strong selectivity toward methanol production (>92%), more than one order of magnitude higher than that for the Ni3Ga1 NPs, which we ascribe to the presence of the δ-Ni5Ga3 phase.
Category: Chemistry
[2] viXra:2205.0033 [pdf] submitted on 2022-05-06 20:07:34
Authors: Viktor Ulrich, Boris Moroz, Pavel Pyrjaev, Ilya Sinev, Andrey Bukhtiyarov, Evgeny Gerasimov, Valerii Bukhtiyarov, Beatriz Roldan Cuenya, Wolfgang Grünert
Comments: 48 Pages.
Three-way catalysts containing Au and/or Pd supported on either CeZrOx (CZ) or La2O3/Al2O3 (LA) were studied with respect to their performance in a model feed and characterized by various techniques (physisorption, CO chemisorption, TEM, XRD, XPS, XANES). A drastic support influence was found in both catalytic behavior and Pd-Au relation. While Au was a strong poison for all catalytic functions of Pd (oxidation, NO reduction) on LA, poisoning was much mitigated on CZ, rendering all Pd containing catalysts superior to a commercial reference. After ageing, the poisoning by Au was aggravated on LA. On CZ, Pd-rich bimetallic combinations retained better activity than Pd/CZ, which still outperformed the reference. As Au did not significantly contribute to propene oxidation and NO reduction, activity of Pd was markedly increased under a promoting influence of Au. Stabilization of PdII by ceria and delayed Pd-Au alloy formation are key features in the CZ-supported PdAu catalysts.
Category: Chemistry
[1] viXra:2205.0032 [pdf] submitted on 2022-05-06 10:34:13
Authors: Rubén Rizo, Arno Bergmann, Janis Timoshenko, Fabian Scholten, Clara Rettenmaier, Hyo Sang Jeon, Yen-Ting Chen, Aram Yoon, Alexander Bagger, Jan Rossmeisl, Beatriz Roldan Cuenya
Comments: 38 Pages.
Direct ethanol fuel cells are among the most promising clean electrochemical power sources. Nevertheless, the high cost and low efficiency of the Pt-based catalysts hinder their commercialization. Here, Pt-Sn-Co nanocubes with a Pt- and Sn-rich shell show improved performance towards the electrochemical ethanol oxidation reaction. Mechanistic and structural insights were obtained by synergistically combining different in situ and operando spectro-electrochemical techniques, including electrochemical mass spectrometry, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. In particular, electrochemical conditioning and EOR were found to induce Sn leaching from the core and shell, leading to electrochemically-accessible Pt sites adjacent to partially-oxidized Sn sites on a Pt3Co-like core. The increased activity of the Pt-Sn-Co nanocubes was assigned to the formation of a higher amount of C1 (CO2) and C2 (acetic acid/acetaldehyde) products during EOR as well as to their high ability to remove adsorbed CO from the Pt surface when compared to similarly-sized cubic Pt-Sn or Pt NPs. Beneficial strain and ligand effects are combined here through a catalyst design resulting in adjacent Pt and Sn sites at the overlayer on top of a Pt3Co alloy core.
Category: Chemistry
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