High-Throughput Spatial-Resolution Mapping of Acid Sites in Amorphous Nanoparticles via Synchrotron Infrared Microscopy

Brønsted and Lewis acid sites (LAS) are the fundamental active centers in heterogeneous catalysis, playing distinct yet complementary roles in driving catalytic reactions. Together, they govern the catalyst’s reactivity and selectivity by enabling multiple reaction pathways. While significant advances have been made in developing experimental methods for the quantitative analysis of acid sites, several challenges remain unresolved. These include: (a) the inability to directly observe the micro- to nanoscale structure of acidic sites, especially those located at step edges and surface defects; (b) difficulty in distinguishing the dynamic behavior of Brønsted and Lewis acid sites during chemisorption and physisorption; and (c) the lack of real-time spatially resolved acidity understanding across heterogeneous catalyst surfaces. Here, high-spatial-resolution mapping of acid sites in nanoparticles using synchrotron-based infrared microspectroscopy was elucidated by using pyridine as a probe molecule. This approach enables direct 2D spatial mapping and temperature-resolved analysis of Brønsted and Lewis acid sites in amorphous nanoparticles and micrograins, providing insights into the distribution and nature of acidity at the micro- to nanoscale.