Ceria-supported Pd catalysts with different size regimes ranging from single atoms to nanoparticles for the oxidation of CO

• Published in: Journal of catalysis 2022-03, Vol.407, p.104-114
• Main Authors: Ma, Kexin, Liao, Weiqi, Shi, Wen, Xu, Fangkai, Zhou, Yan, Tang, Cen, Lu, Jiqing, Shen, Wenjie, Zhang, Zhenhua
• Format: Article
• Language: English
• Subjects: Catalytic mechanism; CO oxidation; CO-PROX; Pd/CeO2; Size effect
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2022.01.023

[Display omitted] •CeO2-supported single Pd atoms are the most intrinsically active in CO oxidation.•The CO reaction rate on isolated Pd sites is exclusively promoted by H2.•The oxidation of CO proceeds through a Langmuir-Hinshelwood mechanism.•The decomposition of formate species contribution dominantly in CO oxidation.•A stronger H-spillover effect was observed on isolated Pd sites.•Bridged-OH contributes to the consumptions of bicarbonate and formate species. Supported metal catalysts are the most widely used in industrial processes and the metal particle size plays a crucial factor in determining the catalytic performance. Herein, CeO2-supported Pd catalysts with different Pd size regimes ranging from single atoms, to nanoclusters (1–2 nm), and to nanoparticles (>2 nm) were used for both CO oxidation and preferential oxidation of CO in H2 (CO-PROX). Compared to Pd nanoclusters and nanoparticles, CeO2-supported single Pd atoms (PdSA/CeO2) are the most intrinsically active in CO oxidation, with an apparent activation energy of ca. 40 kJ mol−1. Results of kinetic investigations and in situ diffuse reflectance infrared Fourier transformed spectroscopy demonstrate the CO oxidation proceeding through a Langmuir-Hinshelwood mechanism with the decomposition of formate species acting dominantly as the rate-determining step. The CO reaction rate is exclusively promoted on PdSA/CeO2 catalysts for the CO-PROX reaction, which could be ascribed to a stronger H-spillover effect on isolated Pd sites to produce bridged-OH on CeO2 surface, simultaneously facilitating the consumptions of bicarbonate and formate species. There results greatly deepen the fundamental understanding of the Pd size regimes over Pd/CeO2 catalysts for the oxidation of CO.