(308c) The Influence of Dispersion of Pt Supported on Fe/Dealuminated Beta Zeolite on the Kinetics of Propane Dehydrogenation

The catalysis community has shown significant enthusiasm for the utilization of atomically dispersed noble metal catalysts. The process of downsizing metal nanoparticles to achieve isolated, uniform metal sites offers multiple advantages, including enhanced utilization of metal. Nevertheless, the stabilization of atomically dispersed species poses a formidable challenge in propane dehydrogenation conditions, primarily due to Pt atoms’ tendency to agglomerate at elevated temperatures. To address this challenge, our approached has been centered on the creation of numerous Fe anchoring sites on dealuminated BEA (SiBEA) support, facilitating a strong Fe-Pt bond to stabilize dispersed Pt atoms. The resultant Pt-Fe catalysts, featuring varying Pt loadings, have displayed notable performance metrics: selectivity (>96%), conversion (15-28%), propene formation rates (7-53 propene mol/Pt mol.s), and excellent thermal stability in presence of hydrogen at 550°C. Despite hydrogen’s traditional role in enhancing catalyst stability, a comprehensive kinetic study assessing its influence on propene formation rates, particularly concerning Pt particle size, has been clearly absent.

In this study, we undertake an in-depth exploration of hydrogen and propane partial pressure effects on propene formation rates, examining five catalysts with varying Pt weight loadings (ranging from 0.02% to 0.08% Pt) grafted onto Fe/SiBEA zeolite. Notably, our observations reveal two distinct trends in rate dependence on hydrogen partial pressure, depending on Pt particle size. The findings suggest a shift in Pt speciation as Pt particle size reduces, leading to independence of propene formation rate from hydrogen partial pressure, and accompanied by a decrease in apparent activation energy. After fitting the kinetics models, it becomes apparent that the first C-H activation step remains the rate-determining step as Pt particle size increased. However, the abstracted hydrogen migrates to a neighboring Pt atom when Pt is present in clusters. The transition from Pt clusters to isolated Pt sites was confirmed by CO-FTIR, XAFS, and HAADF-STEM.