Pd model catalysts on clean and modified HOPG: Growth, adsorption properties, and stability

Kettner, Miroslav; Stumm, Corinna; Schwarz, Matthias; Schuschke, Christian; Libuda, Jörg

doi:10.1016/j.susc.2018.08.022

Cited by 21 publications

(36 citation statements)

References 49 publications

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“…The sample was annealed at 800 K for 3 min in UHV to remove residual gases. The HOPG sample was bombarded with Ar + (0.5 keV, 300 K, 60 min, 8 × 10 –5 mbar) to create the nucleation sites necessary for the growth of Pd NPs. , Pd was deposited from a wire (Alfa Aesar, 99.9% metals basis, d = 1 mm) loaded into a commercial electron beam evaporator (Focus EFM3). The deposition of Pd for 36 min (flux of 3 nA) at a sample temperature of 300 K led to the formation of a Pd film with an equivalent thickness of 15 Å, which was calibrated by a quartz crystal microbalance.…”

Section: Methodsmentioning

confidence: 99%

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles

et al. 2021

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Solid catalysts with ionic liquid layers (SCILLs) are heterogeneous catalysts coated with a thin layer of an ionic liquid (IL) to improve their selectivity. In this study, we investigated the interplay of the room-temperature IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C 4 C 1 Pyr][NTf 2 ] with transition metal surfaces of both Pd(111) single crystals and Pd nanoparticles (NPs) supported on highly oriented pyrolytic graphite (HOPG). To this end, we combine theoretical insights obtained by density functional theory (DFT) and molecular dynamics (MD) calculations with experimental data acquired via time-resolved infrared reflection absorption spectroscopy (TR-IRAS) performed under ultrahigh vacuum (UHV) conditions. IL monolayer films formed on Pd(111) and Pd NPs are strongly bound to the surface via the SO 2 moiety of the [NTf 2 ] − anion. By combination of IRAS, DFT, and MD, we identify the most common adsorption motifs. Most importantly, the binding motif of the anion changes as a function of the IL coverage. On supported Pd NPs, additional effects arise from the particle morphology and from the diffusion of carbon from the support to the Pd NPs. Our results suggest that the effect of the IL film on the catalytic activity should strongly depend on the local coverage and the morphology of the catalyst NPs.

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Section: Methodsmentioning

confidence: 99%

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles

et al. 2021

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“…Subsequently, the sample was annealed at 800 K for 3 min in UHV. The HOPG samples were bombarded with Ar + (Linde 6.0, 500 eV, 60 min, ∼3.0 μA/cm 2 ) at a sample temperature of 300 K to create nucleation centers for the growth of Pt NPs . Pt was deposited from a wire (Alfa Aesar, 99.95% purity, 1 mm in diameter) using a commercial electron beam evaporator (Focus EFM3).…”

Section: Methodsmentioning

confidence: 99%

“…The HOPG samples were bombarded with Ar + (Linde 6.0, 500 eV, 60 min, ∼3.0 μA/cm 2 ) at a sample temperature of 300 K to create nucleation centers for the growth of Pt NPs. 83 Pt was deposited from a wire (Alfa Aesar, 99.95% purity, 1 mm in diameter) using a commercial electron beam evaporator (Focus EFM3). After the deposition of Pt for 45 min at a flux of 17 nA and a sample temperature of 300 K, we obtained a Pt film with an equivalent thickness of 15 Å as determined by a quartz crystal microbalance.…”

Section: Methodsmentioning

confidence: 99%

Dynamic CO Adsorption and Desorption through the Ionic Liquid Layer of a Pt Model Solid Catalyst with Ionic Liquid Layers

et al. 2019

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Solid catalysts with ionic liquid layers (SCILLs) have recently attracted a lot of attention, as the ionic liquid (IL) coating can give rise to drastically improved selectivity. Here, we studied the interaction of the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-imide [C 4 C 1 Pyr]-[NTf 2 ] with Pt(111) and Pt nanoparticles (NPs) on highly oriented pyrolytic graphite under ultrahigh vacuum conditions. The IL film on Pt(111) and on the Pt NPs consists of a strongly bound monolayer and a weakly bound bulk phase. In the monolayer, [NTf 2 ] − adopts cis conformation and binds via the SO 2 groups. Adsorption of [NTf 2 ] − at Pt defect sites is preferred to adsorption at terraces, whereas preadsorbed CO blocks the adsorption at defects. Further, IL coadsorption leads to desorption and displacement of on-top CO on terraces, whereas CO resides in the bridging position. IL multilayers desorb at 380 K, whereas the strongly adsorbed monolayer on Pt resides and gradually desorbs and decomposes between 400 and 500 K. Finally, we studied the permeability of IL layers for CO by pressure modulation experiments in combination with in situ infrared reflection absorption spectroscopy. We show that the IL multilayer completely blocks CO adsorption, whereas CO easily penetrates the IL monolayer film and forms a mixed adsorbate phase. It is noteworthy that dynamic CO adsorption is much more facile on Pt NPs than on Pt(111). Our results suggest that strongly adsorbed IL monolayers may play an important role in real SCILLs.

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“…19,25,26 The consequences of such modification by Ar + or O + bombardment were described in our previous publication. 22 Here, we prepared Pt−Ga SCALMS-like model systems by physical vapor deposition (PVD) of Ga and Pt onto HOPG modified by Ar + bombardment. The Pt−Ga system has been studied in the past with respect to formation of various intermetallic compounds (IMCs).…”

Section: Introductionmentioning

confidence: 99%

Pt–Ga Model SCALMS on Modified HOPG: Thermal Behavior and Stability in UHV and under Near-Ambient Conditions

et al. 2020

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We have prepared model systems for Pt–Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pt and Ga onto highly oriented pyrolytic graphite (HOPG). Prior to metal deposition, the HOPG support was modified by Ar+ bombardment. In this work, we focus on the stability of the Pt–Ga deposits toward agglomeration, which is a critical challenge in application. Specifically, we study the behavior of the model catalysts in ultrahigh vacuum (UHV) and under near ambient pressure (NAP) conditions at different temperatures. We use CO as a probe molecule to examine changes in the surface composition of the Pt–Ga deposits by in situ infrared reflection absorption spectroscopy (IRAS). In specific, we combine IRAS and ex situ atomic force microscopy (AFM) to study changes induced by annealing. We find that sintering effects are strongly dependent on the thickness of the deposited Pt–Ga layers. Our data suggest that particle ripening leads to a separation of the system into disperse Pt-rich and large Ga-rich particles. In the NAP regime, we performed simultaneous measurements with polarization modulation IRAS (PM-IRAS) and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The alloying of Pt and Ga is accompanied by a shift of Pt 4f and Ga 3d photoelectron lines to higher binding energies. Although partial oxidation of Ga is observed upon CO exposure at pressures in the millibar regime, PM-IRAS shows adsorbed CO at a frequency typical for Pt ensembles in a Ga matrix.

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Pd model catalysts on clean and modified HOPG: Growth, adsorption properties, and stability

Cited by 21 publications

References 49 publications

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles

Dynamic CO Adsorption and Desorption through the Ionic Liquid Layer of a Pt Model Solid Catalyst with Ionic Liquid Layers

Pt–Ga Model SCALMS on Modified HOPG: Thermal Behavior and Stability in UHV and under Near-Ambient Conditions

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Pd model catalysts on clean and modified HOPG: Growth, adsorption properties, and stability

Cited by 21 publications

References 49 publications

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C4C1Pyr][NTf2] on Pd Single Crystals and Nanoparticles

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C4C1Pyr][NTf2] on Pd Single Crystals and Nanoparticles

Dynamic CO Adsorption and Desorption through the Ionic Liquid Layer of a Pt Model Solid Catalyst with Ionic Liquid Layers

Pt–Ga Model SCALMS on Modified HOPG: Thermal Behavior and Stability in UHV and under Near-Ambient Conditions

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A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles

A Molecular View of the Ionic Liquid Catalyst Interface of SCILLs: Coverage-Dependent Adsorption Motifs of [C₄C₁Pyr][NTf₂] on Pd Single Crystals and Nanoparticles