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. 2021 Nov 25;12(1):6888.
doi: 10.1038/s41467-021-27238-z.

Molecular-level insights into the electronic effects in platinum-catalyzed carbon monoxide oxidation

Wenyao Chen  1 , Junbo Cao  1 , Jia Yang  2 , Yueqiang Cao  1 , Hao Zhang  3   4 , Zheng Jiang  4   5 , Jing Zhang  1 , Gang Qian  1 , Xinggui Zhou  1 , De Chen  6 , Weikang Yuan  1 , Xuezhi Duan  7
Affiliations

Molecular-level insights into the electronic effects in platinum-catalyzed carbon monoxide oxidation

Wenyao Chen et al. Nat Commun. .

Abstract

A molecular-level understanding of how the electronic structure of metal center tunes the catalytic behaviors remains a grand challenge in heterogeneous catalysis. Herein, we report an unconventional kinetics strategy for bridging the microscopic metal electronic structure and the macroscopic steady-state rate for CO oxidation over Pt catalysts. X-ray absorption and photoelectron spectroscopy as well as electron paramagnetic resonance investigations unambiguously reveal the tunable Pt electronic structures with well-designed carbon support surface chemistry. Diminishing the electron density of Pt consolidates the CO-assisted O2 dissociation pathway via the O*-O-C*-O intermediate directly observed by isotopic labeling studies and rationalized by density-functional theory calculations. A combined steady-state isotopic transient kinetic and in situ electronic analyses identifies Pt charge as the kinetics indicators by being closely related to the frequency factor, site coverage, and activation energy. Further incorporation of catalyst structural parameters yields a novel model for quantifying the electronic effects and predicting the catalytic performance. These could serve as a benchmark of catalyst design by a comprehensive kinetics study at the molecular level.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Strategy to bridge the microscopic-to-macroscopic transition.
Schematic diagram of bridging the upscaling gap between the microscopic fingerprints of active sites and the macroscopic catalytic performance based on (in situ) spectroscopy/microscopy characterization, isotopic labeling technique, DFT calculations and in situ kinetics measurements for CO oxidation.
Fig. 2
Fig. 2. Strategy for designing, preparing, and characterizing Pt catalysts.
a Schematic diagram of CNT activations via covalent functionalization and heat treatment. The yellow and light blue surfaces correspond to the electron increase and depletion zones, respectively. b The particle size and binding energy (B.E.) of Pt for Pt/CNT-0, Pt/CNT-200, Pt/CNT-400, Pt/CNT-600, Pt/CNT-800 and Pt/CNT-1000. c Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, the corresponding fast Fourier transform (FFT) pattern, and projection of a truncated octahedron model of the Pt/CNT-600 catalyst. The EPR spectra (d), Pt L3-edge XANES profiles (e), and the relationship between nEWG/nEDG and Pt B.E., Pt charge as well as EPR intensity (f) for Pt/CNT-0, Pt/CNT-200, Pt/CNT-400, Pt/CNT-600, Pt/CNT-800, and Pt/CNT-1000.
Fig. 3
Fig. 3. Catalytic testing and DFT calculations of CO oxidation.
a CO conversion as a function of temperature. The reaction rate (r100) and the corresponding TOFPt and TOFCO at 100 °C (b), as well as the relationships between r100, TOFPt, TOFCO and Pt charge (c), for Pt/CNT-0, Pt/CNT-200, Pt/CNT-400, Pt/CNT-600, Pt/CNT-800 and Pt/CNT-1000. Potential energy diagram from DFT calculations and the schematic diagram of the related configurations over Pt-basal (d), and the corresponding energy barrier (e) for CO oxidation over Pt-basal, Pt-hydroxyl, Pt-carboxyl, Pt-carbonyl, and Pt-ester. f The relationships between energy barrier (ΔEi), adsorption energy (Eads) and Pt Bader charge. g The relationship between the activation energy (Ea) and the proposed energy barrier (ΔE), incorporating the influences of the above OCGs (Supplementary Information), for Pt/CNT-0, Pt/CNT-200, Pt/CNT-400, Pt/CNT-600, Pt/CNT-800, and Pt/CNT-1000.
Fig. 4
Fig. 4. Isotopic labeling studies and SSITKA of CO oxidation.
a Mass spectrometry (MS) data collected for the Pt/CNT-600 catalyst during the switch from Ar to Ar+C16O + 16O2 (the purity is >99.99%), Ar+C16O + 16O2 (50%)/18O2 (50%), and Ar+C16O + 18O2 (the concentration of 18O2 is > 97%) at an ambient pressure. b The relationship between logarithm of frequency factor (lnAi) and activation energy (Ea). The Ea (c), r100’ (d), site coverages of CO (θCO) and oxygen (θoxygen) (e), logarithm of frequency factor (lnA0’) (f), as well as the experimental and predicted TOFʹ (g) as a function of Pt charge for Pt/CNT-0, Pt/CNT-200, Pt/CNT-400, Pt/CNT-600, Pt/CNT-800, and Pt/CNT-1000. Reaction conditions: 100 °C, PCO:PO2:PAr = 1:20:79, and 60,000 mL∙gcat−1 ∙ h−1. Error bars in b and c were calculated from the standard error of each linear fit presented in Supplementary Fig. 26.
Fig. 5
Fig. 5. In situ electronic structure characterization.
In situ XPS Pt 4f spectra of Pt/CNT-600 under the reaction atmosphere at elevated temperature.
Fig. 6
Fig. 6. Model derivation of CO oxidation.
Schematic diagram of model derivation for Pt-catalyzed CO oxidation based on theoretical calculations and experimental investigations.
See this image and copyright information in PMC

References

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