Shedding New Light on Nanostructured Catalysts with Positron Annihilation Spectroscopy. Issue 12 (25th September 2018) - Mitchell, Sharon
Abstract: Interest in new tools for the analysis of catalytic materials is growing due to the potential to enhance their functionality through the optimal nanostructuring, for example, of pore networks and surface properties. This prompts the need for improved descriptors to discriminate increasingly complex architectures. As a nondestructive, dynamic, and potentially, temporally, and spatially resolved tool, positron annihilation spectroscopy (PAS) can provide valuable complementary insights to already established (e.g., adsorption, spectroscopy, diffraction, and microscopy) methods. This is possible due to the specific sensitivity of positrons to the electronic environment, which determines their annihilation characteristics. However, despite growing enthusiasm, PAS is not widely known in the catalysis community. This review aims to highlight the many unique features, principles, and potential pitfalls of the technique, expanding on the outdated reviews on the topic, which are now over a decade old. After briefly introducing the principles, progress in the application of PAS to investigate various features of relevant catalytic materials is summarized. This includes the crystalline structure, presence of defects, pore connectivity and evolution, chemical properties, and adsorption phenomena. An improved understanding of the response will contribute not only to guiding the design of nanostructured materials but also to positioning PAS as a mainstream method for catalyst characterization. Abstract : The annihilation of positrons in nanostructured materials depends on the pore architecture and chemical composition. The different variants of positron spectroscopy and the ways in which they can be applied to gain complementary insights into key characteristics of catalysts such as zeolites, metal–organic frameworks, and layered double hydroxides are reviewed.