Speciation of Pt in Ultra-Low Formulations Using CO Combustion as a Probe Reaction

Determining the dispersion and speciation of Pt catalysts containing ultra-low loadings (Pt < 3000 ppm) remains a significant challenge in heterogeneous catalysis because conventional characterization techniques are often limited by insufficient sensitivity, spatial resolution, and detection limit. This study is focused on the development of a high-throughput CO combustion methodology for the fast quantitative determination of Pt dispersion in catalysts with ultra-low Pt loadings under strict kinetic control conditions. This approach was combined with XPS, H2 and CO chemisorption, CO-DRIFTS, XAFS, and TEM to calibrate the methodology and provide mechanistic insights into the influence of Pt coordination and electronic state on CO combustion activity. A linear correlation was found between the CO oxidation rate (μmol CO converted/g-cat/min) and the platinum surface area assessed by chemisorption. Using Pt-XANES, XPS and CO-DRIFTS techniques, it was shown that both cationic and metallic Pt species are present in fresh Pt/Al2O3 materials after calcination in air, and cationic Pt is less active than metallic Pt for CO oxidation. The fraction of Pt cationic sites can be estimated by using the CO oxidation rates on as synthesized and reduced catalysts.