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

9803752研究人员模拟并分析了最近在非常薄的晶体上的催化化学反应研究中发现的机械化学不稳定性：反应速率的时空变化与热释放相结合，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，放热和变形之间的循环;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中模式形成和不稳定性的经验基础上。 梁的非线性屈曲约束下的理论和计算研究扩展到占静态以及动态变化的梁的属性，包括热致应变。 早期的计算机辅助研究图案形成的催化剂表面上被用来驱动，通过温度场，从而产生，机械变形的催化剂。 最后，通过允许变形来改变表面催化性质，从而试图再现实验中观察到的振荡，从而闭合环。 建模、稳定性分析和计算机辅助工作是在与普林斯顿（非均匀梁）和柏林（催化晶体变形）的实验组不断对话中进行的。多相催化反应构成了工业和环境相关化学过程的支柱：例如，该项目所涉及的CO氧化反应发生在每一个汽车催化转化器中。 用于分析在反应条件下原位催化剂上发生的精细空间和时间细节的技术的发展正在彻底改变这些过程的建模方式，并使新现象的发现成为可能。 这将反过来改善催化过程的设计。 具体而言，该项目旨在了解最近才在CO氧化中观察到的现象：涉及催化剂机械变形与温度和化学浓度耦合的振荡。 计算机辅助分析的过程导致更好的，预测模型，可以利用优化材料性能和操作条件的过程。 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.