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Contenuto archiviato il 2022-12-23

Experimental and theoretical studies of temporal and spatial self-organisation processes in oxidative reactions over platinum group metals: An approach to bridge the gap between single crystals and nano-size supported catalyst particles.

Obiettivo

The ultimate objective of the project is to understand on the molecular level the various kinds of non-linear processes during oxidative reactions over platinum group metals on various levels of catalytic systems: to bridge the structure and pressure gap between single crystals and nanometer supported catalyst particles. The reaction kinetics on the supported metal catalyst may be quite different as compared to that on the single crystal surfaces, as a result of interplay between different nanoplanes present on small particles. These surfaces, with a crystallite size of 100-300 Å, are mainly formed by the most densely packed nanoplanes, which differ dramatically in adsorption and oscillation behaviour. The effort therefore will rely on studying these phenomena in the case of model reactions (CO+O2, H2+O2, CO+NO, NO+H2, NOx reduction) over catalysts varying from single crystal surfaces at low pressures up to supported catalysts at normal pressure - as pressure gap levels. The increasing complexity of the systems will be approached by modeling and simulation of the coupling and synchronization of local oscillators, the mechanism of which will be evaluated at low-pressure single crystal studies. A new understanding of heterogeneous catalytic processes could arise by paying attention to spatiotemporal self-organization (regular and chaotic oscillations in reaction rate, the formation of spatial surface structures and chemical waves) due to their highly non-linear character. Three different macroscopic, microscopic and atomic analytical tools will be applied to learn details about reaction dynamics at catalyst surfaces.
The FEM and FIM microscopies will be used to perform in situ investigations of real dynamic surface processes on an atomic level in which different crystallographic nano-size planes of a sharp tip are simultaneously exposed to the reacting gas. STM microscopy with atomic resolution will be used for the imaging of the surface defects at oscillatory reaction conditions. Chemical wave patterns will be investigated on noble metal single crystal surfaces on a microscopic level by employing spatially resolving PEEM (1 µm resolution). During catalytic reactions the propagation of the chemical waves will be observed due to the coupling between an autocatalytic reaction and diffusion of reactants or global coupling via the gas phase. The intimate mechanism of self-organization of the reactions over large single crystal surfaces, model nano-size crystallites on a planar oxide supports or a zeolite matrix will be studied on the macroscopic level using the unique variety of contemporary physical methods for metal surface investigation: HREELS, LEED, WF, TDS, TPR, WF, ESES. Reliable information concerning kinetic parameters and the reaction mechanism will be obtained with the help of mathematical modelling of the experimental data.

In our approach, the study of the similarities and differences of oscillatory reaction behaviour over nanometer and macroscopic catalytic surfaces novel results will be obtained directed to:
- elucidation of "the structure-gap" and "the pressure-gap" by investigation of the same catalytic reactions on platinum group metal samples varying from single crystals -> sharp tips -> nm metal particles at low pressures up to model supported catalysts at normal pressure on the atomic and molecular scale;
- solution of the problem, concerning chemical wave formation and synchronization of local oscillators on various levels: single crystals - sharp tips - metal nano-size particles;
- study of the metal particle size effect at reaction rate oscillations;
- improvement of catalytic concepts as spillover or synergistic effect over alloy surfaces to control the activity and selectivity of catalytic reactions;
- establishment of the role of heat transfer in the synchronization of inhomogeneous parts of the catalyst layer;
- development of realistic mathematical models, describing the oscillatory behaviour and chemical waves formation on different levels of the catalytic systems under study;
- modification of quantum-chemical technique for calculations of the local electron density.
The results will lead to new concepts of heterogeneous catalysis. Ultimately, our approach may lead to the development of a novel generation of catalysts.

Invito a presentare proposte

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Meccanismo di finanziamento

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Coordinatore

Leiden University
Contributo UE
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Indirizzo
Einsteinweg 55
2300 RA Leiden
Paesi Bassi

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Costo totale
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Partecipanti (6)