The investigators model and analyze a mechano-chemical instability recently discovered in the study of catalytic chemical reactions on very thin crystals: spatiotemporal variation in the reaction rate coupled with heat release causes spatially varying thermal expansion and buckling of the catalyst surface. This changes the catalytic properties, closing the loop between reaction, heat release and deformation; it has been observed to lead to sustained mechano-chemical oscillations. The project builds on experience in studying pattern formation and instability independently in mechanical and in chemically reacting systems. Theoretical and computational studies of nonlinear buckling of beams under constraints are extended to account for static as well as dynamic variations of the beam properties, including thermally-induced strains. Earlier computer-assisted studies of pattern formation on catalytic surfaces are used to drive, through the temperature fields thereby generated, mechanical deformations of the catalyst. Finally, the loop is closed by allowing the deformation to change the surface catalytic properties, thus attempting to reproduce the oscillations observed in experiments. The modeling, stability analysis and computer-assisted work are performed in constant dialogue with experimental groups in Princeton (on inhomogeneous beams) and in Berlin (on deforming catalytic crystals).
Heterogeneous catalytic reactions constitute the backbone of chemical processes of industrial and environmental relevance: the CO oxidation reaction the project addresses occurs, for example, in every automotive catalytic converter. The development of techniques for analyzing in fine spatial and temporal detail what occurs on the catalyst in situ under reaction conditions is revolutionizing the way modeling of these processes is done and enabling the discovery of new phenomena. This will in turn improve the design of catalytic processes. Specifically, this project aims at understanding a phenomenon only recently observed in CO oxidation: oscillations involving mechanical deformations of the catalyst coupled to temperature and chemical concentrations. Computer-aided analyses of the process lead to better, predictive models, which can be exploited in optimizing both the material properties and the operating conditions of the process. Funding for the project is provided by the program of Computational Mathematics and the Office of Multidisciplinary Activities in MPS and by the Chemical Reaction Processes program in ENG.
