Spatial and Magnetic Factors for CH4 Oxidation on Pd Slabs in the Presence of Transition-Metal Me Cations Exchanged in γ-Al2O3 Support or MeAl2O4 Spinels, Me = Ni, Co, Mn
| Autor: | Alexander V. Larin, Ralitsa Velinova, S. Todorova, I. A. Bryukhanov, A.A. Rybakov, A. Naydenov |
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| Rok vydání: | 2020 |
| Předmět: |
Materials science
02 engineering and technology 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Surfaces Coatings and Films Electronic Optical and Magnetic Materials Catalysis Crystallography General Energy Transition metal Physical and Theoretical Chemistry 0210 nano-technology |
| Popis: | Two variants of the introduction of transition metals (TMs) Me = Ni, Mn, Co into the Pd(100)/(100)γ-Al2O3 catalytic system are presented to reveal a possible influence of TM on the catalytic activity of Pd for CH4 dissociation. Al/Me replacement at the (100)γ-Al2O3 surface is performed at the normal (four-coordinated) or undercoordinated (two-coordinated) Al positions, on the one hand. MeAl2O4 spinel formation is admitted at a stoichiometric Me/Al ratio, on the other hand. The addition of TM to the (100)γ-Al2O3 slab weakly changes the activation energy of CH4 dissociation. The dissociation barrier is higher for the Pd deposited over (100)MeAl2O4 spinels than the barriers over Pd(100)/(100)γ-Al2O3 catalysts. The dissociation barrier grows with a MeAl2O4 cell parameter from Ni to Mn. The minimum barrier over different supports (ZrO2, Al2O3, MeAl2O4) was found for Pd(100) deposited on the defective (100)γ-Al2O3 model. Considering another step of the whole Pd/PdO redox cycle of CH4 oxidation, we evaluated the consequences of large Pd···Pd distances over MeAl2O4 for atomic O diffusion in Pd(100). Higher squares of Pd4 windows, which limit the O jumps, relative to those calculated for transition states in Pd(100)/(100)γ-Al2O3 predict an easier O diffusion in Pd/MeAl2O4. The O2 consumption at lower temperatures in the spinels was tested experimentally using temperature-programmed oxidation (TPO) method and confirmed the easier O2 chemisorption therein compared to Pd(100)/(100)γ-Al2O3. Magnetic TM moments reveal weak changes in the course of CH4 dissociation for both routes of TM addition mainly depending on reordering of Pd geometry and its magnetic moments at both (100)γ-Al2O3 or (100)MeAl2O4. |
| Databáze: | OpenAIRE |
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