In-situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by Sum frequency generation: size and site effect - Archive ouverte HAL
Article Dans Une Revue Physical Chemistry Chemical Physics Année : 2023

In-situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by Sum frequency generation: size and site effect

Résumé

Controlling reactive sites of nanoparticles (NPs) is crucial to improve catalyst efficiency. In this work, Sum-Frequency Generation is used to probe CO vibrational spectra on MgO(100) ultrathin film/Ag(100) supported Pd nanoparticles (NP) ranging from 3 to 6 nm in diameter and compared to coalesced Pd NPs and Pd(100) single crystal. We aim at in-situ evidencing the role played by active adsorption sites on the catalytic CO oxidation reactivity trends varying with NP size. From ultrahigh vacuum to the mbar range and temperatures from 293 K to 340 K, our observations suggest that bridge sites are the main active sites for CO adsorption and catalytic oxidation. On Pd(100) single crystal at 293 K, CO oxidation predominates over CO poisoning for pressure ratio of O2/CO larger than 300; on Pd NPs, both the site coordination due to NP geometry and MgO support-induced (MgO-induced) Pd-Pd interatomic distance change, impact the reactivity trend varying with size in different ways. Edge sites with a low coordination are more reactive than facet sites, while facet with a smaller Pd-Pd atomic length is more reactive than that with a larger one. The interplay of both site and size effects gives rise to a non-monotonic reactivity trend of CO on MgO(100) ultrathin film supported Pd NPs: the reactivity of Pd NPs increases for smaller NP size side due to a higher edge/facet ratio and meanwhile increases for larger NP size side due to the terrace facet with a smaller Pd-Pd atomic length at the NP surface and a lower diffusion barrier.
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Dates et versions

hal-04036212 , version 1 (19-03-2023)

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Jijin Wang, Aimeric Ouvrard, Wanquan Zheng, Serge Carrez, Ahmed Ghalgaoui, et al.. In-situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by Sum frequency generation: size and site effect. Physical Chemistry Chemical Physics, In press, ⟨10.1039/D2CP05740A⟩. ⟨hal-04036212⟩
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