High-Throughput Calorimetric Titration of Active Sites on Metal Oxide-Supported Catalysts with Infrared Thermal Imaging

Metal oxide-supported catalysts play a central role in the chemical industry, with their performance governed by the nature and density of active sites. While chemisorption is widely used for active-site quantification via stoichiometric probe adsorption, it is typically conducted ex situ and lacks spatial resolution, limiting its applicability to high-throughput and in situ analysis. Here, using Pd/Al₂O₃ as a model system, we quantitatively mapped their active-site densities by monitoring the heat released during titration of preadsorbed probe molecules through infrared (IR) thermal imaging. Benefiting from high spatiotemporal resolution and compatibility with reaction-relevant conditions, the developed methodology enabled the high-throughput screening of catalysts with varying Pd loadings and allowed real-time tracking of active-site evolution during in situ thermal aging. Our measurements revealed a fundamental trade-off: although higher Pd loadings increased the absolute number of active sites, they simultaneously accelerated structural evolution under working conditions, resulting in reduced metal utilization and faster catalyst deactivation. Owing to its general applicability to heat-releasing surface processes, this approach provides a versatile platform for active-site assessment across diverse catalyst systems, offering valuable insights into structure-activity-stability relationships and guiding the rational design of more durable catalytic materials.