H2O‑Enabled Switch of the CO Oxidation Pathway on Zeolite-Confined Cationic Pd Catalysts

Understanding reaction-driven dynamics of Pd sites is crucial for rationalizing the design of high-performance Pd-zeolites for environmental and energy catalysis. Using Pd-SSZ-13 zeolite as catalyst, we demonstrate that H2O, an unavoidable component in reality, promoted CO oxidation by facilitating O2 activation on Pd sites. In situ spectroscopic interrogations and QM/MM simulations revealed that the cationic Pd sites, initially coordinated firmly on the zeolite framework, were solvated upon interaction with H2O, forming partially detached Pd–H2O complexes that favored the reaction of CO and O2 via the Langmuir–Hinshelwood mechanism. By contrast, CO on bare Pd site reacts with O2 in the gas phase via the thermodynamically less favorable Eley–Rideal mechanism.