Wild Stefan, Mahr Christoph, Rosenauer Andreas, Risse Thomas, Vasenkov Sergey, Bäumer Marcus
Institute for Applied and Physical Chemistry, University of Bremen, 28359 Bremen, Germany.
MAPEX Center of Materials and Processes, University of Bremen, 28359 Bremen, Germany.
Catal Letters. 2023;153(11):3405-3422. doi: 10.1007/s10562-022-04218-6. Epub 2022 Dec 7.
In this article we shed light on newly emerging perspectives to characterize and understand the interplay of diffusive mass transport and surface catalytic processes in pores of gas phase metal catalysts. As a case study, nanoporous gold, as an interesting example exhibiting a well-defined pore structure and a high activity for total and partial oxidation reactions is considered. PFG NMR (pulsed field gradient nuclear magnetic resonance) measurements allowed here for a quantitative evaluation of gas diffusivities within the material. STEM (scanning transmission electron microscopy) tomography furthermore provided additional insight into the structural details of the pore system, helping to judge which of its features are most decisive for slowing down mass transport. Based on the quantitative knowledge about the diffusion coefficients inside a porous catalyst, it becomes possible to disentangle mass transport contributions form the measured reaction kinetics and to determine the kinetic rate constant of the underlying catalytic surface reaction. In addition, predictions can be made for an improved effectiveness of the catalyst, i.e., optimized conversion rates. This approach will be discussed at the example of low-temperature CO oxidation, efficiently catalysed by npAu at 30 °C. The case study shall reveal that novel porous materials exhibiting well-defined micro- and mesoscopic features and sufficient catalytic activity, in combination with modern techniques to evaluate diffusive transport, offer interesting new opportunities for an integral understanding of catalytic processes.
在本文中，我们阐明了一些新出现的观点，以表征和理解气相金属催化剂孔隙中扩散传质与表面催化过程之间的相互作用。作为一个案例研究，我们考虑了纳米多孔金，它是一个有趣的例子，具有明确的孔隙结构，对完全氧化和部分氧化反应具有高活性。在此，脉冲场梯度核磁共振（PFG NMR）测量能够对材料内的气体扩散率进行定量评估。扫描透射电子显微镜（STEM）断层扫描进一步提供了对孔隙系统结构细节的深入了解，有助于判断其哪些特征对减缓传质最为关键。基于对多孔催化剂内部扩散系数的定量认识，就有可能从测量的反应动力学中分离出传质贡献，并确定潜在催化表面反应的动力学速率常数。此外，还可以对催化剂的改进效率进行预测，即优化转化率。将以低温CO氧化为例讨论这种方法，纳米多孔金在30°C时能有效催化该反应。该案例研究将揭示，具有明确微观和介观特征且具有足够催化活性的新型多孔材料，与评估扩散传输的现代技术相结合，为全面理解催化过程提供了有趣的新机会。
