DYNAMIC HETEROGENEITY: Bifurcations, Patterns and a New Mechano-Chemical Instability

9803752研究人员模拟并分析了最近在极薄晶体上催化化学反应研究中发现的一种机械化学不稳定性：反应速率的时空变化加上热释放导致催化剂表面的空间变化的热膨胀和屈曲。这改变了催化性能，关闭了反应、放热和变形之间的回路；据观察，它会导致持续的机械化学振荡。该项目建立在独立研究机械和化学反应系统的图案形成和不稳定性的经验基础上。梁在约束下的非线性屈曲的理论和计算研究被扩展到考虑梁的静态和动态变化，包括热致应变。早期的催化表面图案形成的计算机辅助研究是用来通过由此产生的温度场驱动催化剂的机械变形。最后，通过允许变形改变表面催化性能来关闭回路，从而试图重现实验中观察到的振荡。建模，稳定性分析和计算机辅助工作是在与普林斯顿（非均匀光束）和柏林（变形催化晶体）的实验组不断对话中进行的。多相催化反应构成了与工业和环境相关的化学过程的支柱：例如，该项目涉及的CO氧化反应发生在每个汽车催化转化器中。在精细的空间和时间细节上分析在反应条件下催化剂上发生的情况的技术的发展正在彻底改变这些过程的建模方式，并使发现新现象成为可能。这将反过来改进催化过程的设计。具体来说，该项目旨在了解最近才在CO氧化中观察到的现象：催化剂的机械变形与温度和化学浓度耦合的振荡。该过程的计算机辅助分析可以产生更好的预测模型，这些模型可以用于优化材料性能和过程的操作条件。该项目的资金由MPS的计算数学计划和多学科活动办公室以及ENG的化学反应过程计划提供。

9803752The 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.