Atomic-Scale Surface Structure and CO Tolerance of NiCu Single-Atom Alloys

Patel, Dipna A.; Hannagan, Ryan T.; Kress, Paul L.; Schilling, Alex C.; Çınar, Volkan; Sykes, E. Charles H.

doi:10.1021/acs.jpcc.9b07513

Cited by 33 publications

(52 citation statements)

References 53 publications

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“…Because the CO adsorption geometry remains upright, the change in site preference produces well separated C-O stretch bands in RAIRS that may be used to identify the presence of monomers vs. dimers of the minority metal component. 9,12,57 Our results suggest that an analogous characterization of Ti ensembles in the Ti-Cu(111) alloy is less feasible using CO RAIRS. We thus emphasize that our CO RAIRS results do not provide direct information about Ti dimers or larger ensembles that may be present in the Ti-Cu(111) alloy and that other characterization methods (e.g., low temperature STM) or probe molecules are needed to identify such structures and quantify their concentrations.…”

Section: Discussionmentioning

confidence: 87%

“…The preference for CO to adsorb in flat-lying geometries on contiguous Ti surface structures is distinct from the behavior of CO adsorbed on dilute alloys of Cu(111) with late transition metals (e.g., Ni, Rh, Pd, Pt), 9,12,57 and has consequences for characterizing Ti-Cu(111) surface alloys. For late transition metal dopants, CO adsorbs into an upright geometry irrespective of the metal ensemble size and exhibits a change in site preference from atop to bridge for isolated dopant atoms vs. larger ensembles.…”

Section: Discussionmentioning

confidence: 99%

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Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

Shi

Owen

Ngan

et al. 2021

The Journal of Chemical Physics

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A single atom Ti-Cu(111) surface alloy can be generated by depositing small amounts of Ti onto Cu(111) at slightly elevated surface temperatures (~500-600 K). Scanning tunneling microscopy shows that small Ti-rich islands covered by a Cu single layer form preferentially on ascending step edges of Cu(111) during Ti deposition below about 400 K, but that a Ti-Cu(111) alloy replaces these small islands during deposition between 500 and 600 K, producing an alloy in the brims of the steps. Larger partially Cu-covered Ti containing islands also form on the Cu(111) terraces at temperatures between 300 and 700 K. After surface exposure to CO at low temperature, reflection absorption infrared spectroscopy (RAIRS) reveals distinct C-O stretch bands at 2102 cm -1 and 2050 cm -1 attributed to CO adsorbed on Cu-covered Ti containing domains vs. sites in the Ti-Cu(111) surface alloy, respectively. Calculations using density functional theory (DFT) suggest that the lower frequency C-O stretch band originates specifically from CO adsorbed on isolated Ti atoms in the Ti-Cu(111) surface alloy, and predicts a higher C-O stretch frequency for CO adsorbed on Cu above subsurface Ti ensembles. DFT further predicts that CO preferentially adsorbs in flat-lying configurations on contiguous Ti surface structures with more than one Ti atom and thus that CO adsorbed on such structures should not be observed with RAIRS. The ability to generate a single atom Ti-Cu(111) alloy will provide future opportunities to investigate the surface chemistry promoted by a representative early transition metal dopant in a Cu(111) host surface.

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Section: Discussionmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

Shi

Owen

Ngan

et al. 2021

The Journal of Chemical Physics

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“…We note that this high tendency for Ni surface aggregation on Ni/Cu(111) alloys in the presence of CO is in qualitative agreement HREELS studies, 64 but also with very recent reflection adsorption infrared spectroscopy studies. 17,68 Thus…”

Section: 2surface Aggregation Of Dopant Atoms In the Presence Of Comentioning

confidence: 99%

Engineering the Surface Architecture of Highly Dilute Alloys: An ab Initio Monte Carlo Approach

2019

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Highly dilute alloys of platinum group metals (PGMs)-(Pt, Rh, Ir, Pd, and Ni) with coinage metals (Cu, Au and Ag) serve as highly selective and coke-resistant catalysts in a number of applications. The catalytic behaviour of these materials is governed by the size and shape of the surface "ensembles" of PGM atoms. Therefore, establishing a means of control over the topological architecture of highly dilute alloy surfaces is crucial to optimising their catalytic performance. In the present work, we use on-lattice Monte Carlo (MC) simulations that are parameterised by density functional theory (DFT) derived energetics, in order to investigate the surface aggregation of PGM atoms under vacuum conditions and in the presence of CO. We study several highly dilute alloy surfaces at various PGM loadings, including Pd/Au(111), Pd/Ag(111), Pt/Cu(111), Rh/Cu(111), Ir/Ag(111) and Ni/Cu(111). Under vacuum conditions, we observe a thermodynamic preference for dispersion of PGM as single atoms in the surface of the coinage metal host, on all examined alloy surfaces except Ir/Ag(111), where Ir atom aggregation and island formation is preferred. By evaluating the alloy surface structure in the presence of CO, we determine that the size and shape of PGM ensembles can be manipulated by tuning the partial pressure of CO (PCO) on the Pd/Au(111), Pd/Ag(111), Ir/Ag(111) and Ni/Cu(111) surfaces. In contrast, we determine that Pt/Cu(111) and Rh/Cu(111) highly dilute alloys are unresponsive to changes in PCO with Rh and Pt dispersing as isolated single atoms within the host matrix, irrespective of gaseous composition. Our findings suggest that it may be possible to fine-tune the surface architecture of highly dilute binary alloys for optimised catalytic performance.

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“…extended Ni(111). [30][31][32] Further evidence for the lower frequency of the IR feature on the SAA comes from our DFT calculations that put this frequency at 1991 cm -1 , which is reasonably accurate when taking into consideration inherent errors in DFT calculations.…”

Section: Resultsmentioning

confidence: 59%

Mechanistic insights into carbon–carbon coupling on NiAu and PdAu single-atom alloys

Kress

Réocreux

Hannagan

et al. 2021

The Journal of Chemical Physics

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Carbon-carbon coupling is an important step in many catalytic reactions and performing sp 3 -sp 3 carbon-carbon coupling heterogeneously is particularly challenging. It has been reported that PdAu single-atom alloy (SAA) model catalytic surfaces are able to selectively couple methyl groups producing ethane from methyl iodide. Herein, we extend this study to NiAu SAAs and find that Ni atoms in Au are active for C-I cleavage and selective sp 3 -sp 3 carbon-carbon coupling to produce ethane. Furthermore, we performed ab initio kinetic Monte Carlo simulations that include the effect of the iodine atom, which was previously considered a bystander species. We find that model NiAu surfaces exhibit a similar chemistry to PdAu, but the reason for the similarity is due to the role the iodine atoms play in terms of blocking the Ni atom active sites. Specifically, on NiAu SAAs the iodine atoms outcompete the methyl groups for occupancy of the Ni sites leaving the Me groups on Au, while on PdAu SAAs, the binding strengths of methyl groups and iodine atoms at the Pd atom active site are more similar. These simulations shed light on the mechanism of this important sp 3 -sp 3 carbon-carbon coupling chemistry on SAAs. Furthermore, we discuss the effect of the iodine atoms on the reaction energetics and make an analogy between the effect of iodine as an active site blocker on this model heterogeneous catalyst and homogeneous catalysts in which ligands must detach in order for the active site to be accessed by the reactants.

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Atomic-Scale Surface Structure and CO Tolerance of NiCu Single-Atom Alloys

Cited by 33 publications

References 53 publications

Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

Engineering the Surface Architecture of Highly Dilute Alloys: An ab Initio Monte Carlo Approach

Mechanistic insights into carbon–carbon coupling on NiAu and PdAu single-atom alloys

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