On the deactivation and regeneration mechanisms of Pd/θ-Al2O3 catalysts for propane oxidation

Abstract

Pd/Al₂O₃ is widely used to eliminate hydrocarbon volatile organic compounds (VOCs) via catalytic oxidation under lean conditions. However, a long-standing issue with this catalytic system is the rapid deactivation of the catalyst due to H₂O poisoning. In this study, we employed a variety of regeneration methods to treat deactivated Pd/θ-Al₂O₃, and then conducted detailed characterizations using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to explore the underlying mechanisms of catalyst deactivation and regeneration. Our findings indicate that only surface hydroxyls that form on PdO or at the PdO-Al₂O₃ boundary exhibit poisoning effects. Among the regeneration methods tested, a reduction treatment with H₂, followed by in situ or ex situ reoxidation, proved to be the most effective in eliminating these poisoning surface hydroxyls and restoring the highly active form of PdO. In contrast, treatment in O₂ at elevated temperatures, although highly efficient in eliminating surface hydroxyls, does not restore the highly active PdO form. This is likely due to adverse high-temperature morphological transformation of PdO that lowers the reactant activation capacity.