Surface Noble Metal Concentration on Ceria as a Key Descriptor for Efficient Catalytic CO Oxidation

Florian Maurer,Maria Casapu,Paolo Dolcet,Felix Studt,Di Wang,Andreas M Gänzler,Jelena Jelic,Stefan Mangold,Christian Kübel,Matthias Stehle,Arik Beck,Wu Wang,Jan-Dierk Grunwaldt

doi:10.1021/acscatal.1c04565

Abstract

During the CO oxidation over metallic Pt clusters and Pt nanoparticles in Pt/CeO2 catalysts, we found that the Pt surface concentration is a key descriptor for the reaction rate. By increasing the surface noble metal concentration (SNMC) of a Pt/CeO2 catalyst by a factor of ∼4, while keeping the weight hourly space velocity constant, the ignition temperature of CO oxidation was decreased by ∼200 °C in the as-prepared state. Moreover, the stability was enhanced at higher SNMC. Complementary characterization and theoretical calculations unraveled that the origin of this improved reaction rate at higher Pt surface concentrations can be traced back to the formation of larger oxidized Pt-clusters and the SNMC-dependent aggregation rate of highly dispersed Pt species. The Pt diffusion barriers for cluster formation were found to decrease with increasing SNMC, promoting more facile agglomeration of active, metallic Pt particles. In contrast, when Pt particle formation was forced with a reductive pretreatment, the influence of the SNMC was temporarily diminished, and all catalysts showed a similar CO oxidation activity. The work shows the general relevance of the proximity influence in the formation and stabilization of active centers in heterogeneous catalysis.

Highlights

Platinum group metals supported as nanoparticles (NPs) on metal oxide carriers are employed in environmental and hydrogenation catalysis, electrocatalysis, or energy-related processes.[1−4] High-surface-area carriers are typically used to stabilize the NPs, which ensures a high ratio of surface-to-bulk atoms for the active species
By systematically varying the surface noble metal concentration of a well-defined Pt/CeO2 catalyst, we found that the chemical and catalytic properties of the oxidized catalysts are strongly correlated to this descriptor
The promotion of Pt species migration at high surface noble metal concentration (SNMC) was substantiated by density functional theory (DFT) calculations, which show that the diffusion barrier for Pt single sites and up to 4-atom clusters decreases, if the interatomic distance diminishes

Summary

INTRODUCTION

Platinum group metals supported as nanoparticles (NPs) on metal oxide carriers are employed in environmental and hydrogenation catalysis, electrocatalysis, or energy-related processes.[1−4] High-surface-area carriers are typically used to stabilize the NPs, which ensures a high ratio of surface-to-bulk atoms for the active species. To unravel the origin of the identified dependence, the structural and electronic properties of the Pt species were tracked during interaction with the gas phase using in situ X-ray absorption, Raman, and infrared spectroscopy Complementary to these SNMC-structure− activity relations, we applied density functional theory calculations to investigate the role of diffusion barriers of highly dispersed Pt species on CeO2 and their influence on the catalytic performance. This is essential for catalytic activity, and the SMNC is a key descriptor for designing supported noble metal catalysts

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSION

■ ACKNOWLEDGMENTS

■ REFERENCES