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Cited by 187Catalytic Processes in Materials ScienceCatalysis and Oxidation ReactionsNanomaterials for catalytic reactions

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Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

Open access
Ouyang, Mengyao, Papanikolaou, Konstantinos G., Boubnov, Alexey, Hoffman, Adam S., Giannakakis, Georgios, Bare, Simon R., Stamatakis, Michail, Flytzani-Stephanopoulos, Maria, Sykes, E. Charles H.·2021·Nature Communications
DOI 10.1038/s41467-021-21555-zPMC PMC7943817
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Abstract

The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

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Figures

Fig. 1 Predicted effect of CO on Pd segregation and aggregation. Initial and final states for (a) Pd segregation; b CO-induced Pd segregation; c Pd–Pd dimer aggregation; d Pd trimer aggregation; e CO-induced Pd–Pd dimer aggregation at different CO fractional coverages; and f CO-induced Pd trimer aggregation at different CO fractional coverages. Values of segregation or aggregation energies are shown on the top of each panel. The given segregation energies in panels (a) and (b) are per Pd atom; negative segregation energy (ΔEseg) values indicate an enthalpic preference for Pd to segregate into the bulk, while positive values indicate a preference for Pd segregation to the surface layer. The reported aggregation energies are given relative to the energy of a SAA; negative aggregation energy (ΔEagg) values imply a preference for Pd atoms to cluster into dimers, whereas when ΔEagg > 0 there is a thermodynamic preference for the SAA phase (i.e., isolated Pd atoms in the Au surface). Panels (g) and (h) show a linear correlation between the CO adsorption energy (Eads(CO)) and the d band center of the d states of the Pd atoms that comprise the adsorption site, and d density of states (DOS) plots in which the DOS are projected onto the same atoms, respectively. Au, Pd, C, and O atoms are shown in yellow, green, gray and red, respectively. The Pd atoms onto which the d DOS are projected in panel (h) are highlighted in the colors of the corresponding DOS plots. In the schematics of the axes, the symbol ◉ denotes an arrow pointing from the page toward the reader.
Fig. 1 Predicted effect of CO on Pd segregation and aggregation. Initial and final states for (a) Pd segregation; b CO-induced Pd segregation; c Pd–Pd dimer aggregation; d Pd trimer aggregation; e CO-induced Pd–Pd dimer aggregation at different CO fractional coverages; and f CO-induced Pd trimer aggregation at different CO fractional coverages. Values of segregation or aggregation energies are shown on the top of each panel. The given segregation energies in panels (a) and (b) are per Pd atom; negative segregation energy (ΔEseg) values indicate an enthalpic preference for Pd to segregate into the bulk, while positive values indicate a preference for Pd segregation to the surface layer. The reported aggregation energies are given relative to the energy of a SAA; negative aggregation energy (ΔEagg) values imply a preference for Pd atoms to cluster into dimers, whereas when ΔEagg > 0 there is a thermodynamic preference for the SAA phase (i.e., isolated Pd atoms in the Au surface). Panels (g) and (h) show a linear correlation between the CO adsorption energy (Eads(CO)) and the d band center of the d states of the Pd atoms that comprise the adsorption site, and d density of states (DOS) plots in which the DOS are projected onto the same atoms, respectively. Au, Pd, C, and O atoms are shown in yellow, green, gray and red, respectively. The Pd atoms onto which the d DOS are projected in panel (h) are highlighted in the colors of the corresponding DOS plots. In the schematics of the axes, the symbol ◉ denotes an arrow pointing from the page toward the reader.CC BY · PubMed Central
Fig. 2 In situ IR data of Pd clustering and redispersion induced by CO. a Schematic illustration of PdAu/SiO2 synthesis in which the final reduction step leads to migration of Pd to the interior of the NPs. CO-DRIFTS results and proposed structures of a Pd0.02Au0.98 /SiO2 sample at 30 °C (b–d), 70 °C (e), 30 °C (f, g), 30 °C (h–j) during 10%CO/He adsorption (AD) (PCO = 0.1 bar) and desorption (DE) process. Prior to the experiment, the sample was reduced at 200 °C in 5% H2/He for 1 h in situ. The labels in the upper right panels indicate the CO adsorption (AD), and desorption processes (DE) via He purge.
Fig. 2 In situ IR data of Pd clustering and redispersion induced by CO. a Schematic illustration of PdAu/SiO2 synthesis in which the final reduction step leads to migration of Pd to the interior of the NPs. CO-DRIFTS results and proposed structures of a Pd0.02Au0.98 /SiO2 sample at 30 °C (b–d), 70 °C (e), 30 °C (f, g), 30 °C (h–j) during 10%CO/He adsorption (AD) (PCO = 0.1 bar) and desorption (DE) process. Prior to the experiment, the sample was reduced at 200 °C in 5% H2/He for 1 h in situ. The labels in the upper right panels indicate the CO adsorption (AD), and desorption processes (DE) via He purge.CC BY · PubMed Central
Fig. 3 Computational investigations of CO-induced Pd clusters formation in Pd/Au. a Fractions of the different surface species (Yk¯) and CO dopant fractional coverage (ΩCO) at temperatures within the 30–70 °C range for Eads(CO) on Pd surface species that are shifted by +0.2 eV as compared to the DFT-predicted values; PCO = 0.1 bar for all calculations. b Representative MC snapshot at 70 °C that shows that the majority of Pd aggregates are Pd–Pd dimers. Pd, Au, and Pd atoms with adsorbed CO are shown in black, yellow, and green, respectively. Bridge sites between Pd atoms, Au atoms covered by CO, and empty hollow sites are shown in light green, blue, and gray, respectively. Panel (b) shows only part of the MC lattice. (c) Yk¯ and ΩCO at four different temperatures for ΩCO ~0.75. The error bars in panels (a) and (c) are ±1 standard deviation.
Fig. 3 Computational investigations of CO-induced Pd clusters formation in Pd/Au. a Fractions of the different surface species (Yk¯) and CO dopant fractional coverage (ΩCO) at temperatures within the 30–70 °C range for Eads(CO) on Pd surface species that are shifted by +0.2 eV as compared to the DFT-predicted values; PCO = 0.1 bar for all calculations. b Representative MC snapshot at 70 °C that shows that the majority of Pd aggregates are Pd–Pd dimers. Pd, Au, and Pd atoms with adsorbed CO are shown in black, yellow, and green, respectively. Bridge sites between Pd atoms, Au atoms covered by CO, and empty hollow sites are shown in light green, blue, and gray, respectively. Panel (b) shows only part of the MC lattice. (c) Yk¯ and ΩCO at four different temperatures for ΩCO ~0.75. The error bars in panels (a) and (c) are ±1 standard deviation.CC BY · PubMed Central
Fig. 4 In situ control over a reaction pathway via CO treatment. Structure (a, c, e) and catalytic performance (b, d, f) of a Pd0.02Au0.98/SiO2 sample after (a, b) no CO treatment, (c, d) CO at 30 °C for 30 min then 70 °C for 30 min which causes Pd to form clusters, (e, f) CO treatment at 30 °C for 30 min, then 70 °C for 30 min, then 30 °C for 1 h which causes Pd to aggregate and then re-disperse back into atoms. g Schematic illustration showing how CO treatment can be used to change Pd from atoms to clusters and back, and the effect of these different active sites on reaction pathway. Ethanol dehydrogenation (EDH) reaction conditions: 300 mg catalyst, 2% ethanol in helium, total flow rate 12 mL/min, GHSV = 2400 mL/(h∙gcat). Each temperature was held for 2 h. The solid line shows the first-round EDH reaction from 150 °C to 400 °C; the dotted line is the second round reaction. Each point is the average of data obtained during 2 h.
Fig. 4 In situ control over a reaction pathway via CO treatment. Structure (a, c, e) and catalytic performance (b, d, f) of a Pd0.02Au0.98/SiO2 sample after (a, b) no CO treatment, (c, d) CO at 30 °C for 30 min then 70 °C for 30 min which causes Pd to form clusters, (e, f) CO treatment at 30 °C for 30 min, then 70 °C for 30 min, then 30 °C for 1 h which causes Pd to aggregate and then re-disperse back into atoms. g Schematic illustration showing how CO treatment can be used to change Pd from atoms to clusters and back, and the effect of these different active sites on reaction pathway. Ethanol dehydrogenation (EDH) reaction conditions: 300 mg catalyst, 2% ethanol in helium, total flow rate 12 mL/min, GHSV = 2400 mL/(h∙gcat). Each temperature was held for 2 h. The solid line shows the first-round EDH reaction from 150 °C to 400 °C; the dotted line is the second round reaction. Each point is the average of data obtained during 2 h.CC BY · PubMed Central

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Research works printed but not linked: 2

  1. Garin, F. Environmental catalysis. Catal. Today 89, 255–268 (2004). · DOI
  2. Hadjiivanov, K. I. & Vayssilov, G. N. Characterization of oxide surfaces and zeolites by carbon monoxide as an IR probe molecule. Adv. Catal. 47, 307–511 (2002). · DOI

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Metadata

Authors
Ouyang, M., Papanikolaou, K. G., Boubnov, A., Hoffman, A. S., Giannakakis, G., Bare, S. R., Stamatakis, M., Flytzani-Stephanopoulos, M., & Sykes, E. C. H.
Affiliations
  • Tufts University (US)
  • Thomas Young Centre (GB)
  • SLAC National Accelerator Laboratory (US)
Corresponding author
Sykes, E. Charles H.
ORCID
Venue
Nature Communications
Publisher
Springer Science and Business Media LLC
Published
2021-03-09
Volume
12
Issue
1
Pages
1549-1549
ISSN
2041-1723 (ISSN-L)
DOI
10.1038/s41467-021-21555-z
PMC
PMC7943817
OpenAlex
W3135341684
Cited by
187
References
93
Citations by year
2026: 25 · 2025: 47 · 2024: 38 · 2023: 31 · 2022: 27 · 2021: 19
FWCI
8.73
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature Communications (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • eScholarship (California Digital Library) (submittedVersion, cc-by)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • UCL Discovery (University College London) (submittedVersion)
  • OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) (submittedVersion)
Funders
U.S. Department of Energy (DE-SC0004738, DE-SC0012573, DE-AC02-76SF00515)
Topics
  • Physical Sciences › Materials Science › Materials Chemistry › Catalytic Processes in Materials Science
  • Physical Sciences › Chemical Engineering › Catalysis › Catalysis and Oxidation Reactions
  • Physical Sciences › Chemistry › Organic Chemistry › Nanomaterials for catalytic reactions
Keywords
single-atom alloy catalysts, active site geometry, palladium clusters, ethanol dehydrogenation, acetaldehyde selectivity, hydrogen selectivity, Monte Carlo simulation, heterogeneous catalysis

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