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Vibrational Spectroscopy for Probing Surfaces in Complex Chemical Environments:
04:30pm - 06:30pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Dr. Baran Eren, Organizer, Weizmann Institute of Science; Ashley Head, Organizer, Lund University; Dr. Baran Eren, Presider, Weizmann Institute of Science; Ashley Head, Presider, Lund University
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Division/Committee: [CATL] Division of Catalysis Science & Technology

The ability to collect spectroscopic data in the presence of gases and liquids has led to new insights into chemical processes at interfaces, with implications for industrial processes. This symposium will explore the vibrational spectroscopies, and their application to heterogeneous catalysis and surface reactions under complex chemical environments will be emphasized.

Wednesday
Heparan sulfate Raman spectroscopy to investigate processes at lithium-ion electrode interfaces
04:30pm - 04:50pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Professor Laurence J Hardwick, Presenter, University of Liverpool
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Fluorescent species are formed during cycling of lithium ion batteries as a result of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyze data due to the spectroscopic overlap of Raman scattering and fluorescence. Within the presentation I will demonstrate how Kerr gated Raman spectroscopy can be used as an effective technique for the isolation of the scattering effect from the fluorescence enabling the collection of the Raman spectra of LiPF6 salt and LiPF6-based organic carbonate electrolyte, without the interference of the fluorescence component. A comparison will be made with FT-Raman using a Laser excitation at 1064 nm, where we show that it is possible to obtain Raman spectra of Li-ion battery relevant materials above a diminished fluorescence background, but with a much lower sensitivity compared to using Kerr Gated Raman with an excitation at 400 nm [1]. Recent data of operando Kerr gated Raman during lithium insertion will also be highlighted.

Wednesday
Surface science study of segregation and CO-induced reconstruction on bimetallic AuPd catalysts
04:50pm - 05:10pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Segregation and CO-induced reconstruction of Pd in AuPd bimetallic catalyst was studied using a 2-dimensional model system where various amounts of Pd were deposited onto a Au(111) single crystal. Combining infrared reflection absorption spectroscopy (IRRAS), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we aim reaching a better understanding of the dynamics of Pd segregation and CO-induced reconstruction in the Pd/Au(111) system. STM results show that as-deposited Pd atoms form islands at low coverages (0.3 ML). After annealing, a surface alloy is formed that implies high surface roughness (Fig. 1a). Pd tends to segregate to the subsurface and this is investigated by STM and IRRAS. CO pressure stabilizes Pd back on the surface by forming both Pd monomers and dimers/trimers at high Pd coverages (>0.38 ML), while only forming Pd monomers at coverages of 0.1 ML. By conducting temperature-programmed IRRAS (TP IRRAS), apparent activation energy of Pd dissolution to Au in the presence of CO can be determined to be 0.48 eV (Fig. 1b and 1c).
Figure 1. (a) STM images of 0.3 ML Pd deposited on a Au (111) single crystal, from left to right: as-deposited surface, after annealing at 473 K and 523 K; (b) TP IRRAS results when heating up the sample with 0.1 ML Pd under a constant CO pressure of 0.1 mbar. (c) Arrhenius plots from 383 K to 453 K to extract the apparent activation energy of Pd dissolution.

Figure 1. (a) STM images of 0.3 ML Pd deposited on a Au (111) single crystal, from left to right: as-deposited surface, after annealing at 473 K and 523 K; (b) TP IRRAS results when heating up the sample with 0.1 ML Pd under a constant CO pressure of 0.1 mbar. (c) Arrhenius plots from 383 K to 453 K to extract the apparent activation energy of Pd dissolution.


Wednesday
Selective hydrogenation reactions over a Pd-Cu(111) single-atom alloy studied with ambient pressure infrared spectroscopy
05:10pm - 05:30pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Michael Trenary, Presenter, University of Illinois at Chicago
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Low coverages of catalytically active metals deposited onto less active metal surfaces can form single atom alloys (SAAs), which often display unique catalytic properties. Such alloys are particularly attractive for selective hydrogenation reactions. We have used reflection absorption infrared spectroscopy (RAIRS) to monitor the hydrogenation of acetylene and propyne over a Pd-Cu(111) SAA. We have also used RAIRS of adsorbed CO to characterize the structure of the SAAs. At certain values of the surface temperature and/or CO pressure, CO adsorbs only on Pd atoms and not on Cu or Ag sites. For low Pd coverages, only CO adsorbed at atop Pd sites is detected. At higher Pd coverages, CO adsorption at Pd bridge sites is observed indicating that Pd-dimers or other aggregates have formed. For acetylene and propyne hydrogenation, polarization dependent RAIRS is used to monitor gas phase reactants and products while simultaneously detecting surface species. No hydrogenation activity is detected on the clean C(111) surface, but hydrogenation to the alkene is readily detected over the Pd-Cu(111) SAA surface. Full hydrogenation to the alkane is not detected. It is also found that coupling reactions occur to produce a carbonaceous layer on the surface, but that hydrogenation proceeds even in the presence of this layer.
Wednesday
Identification of surface intermediates on ZrO2/Cu surfaces during CO2 hydrogenation
05:30pm - 05:50pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Model nanocatalysts prepared by mass-selected deposition of metal oxide and sulfide clusters onto metal surfaces are being studied for CO2 activation and reaction using infrared reflection absorption spectroscopy (IRAS) and x-ray photoelectron spectroscopy (XPS) at near ambient pressures and elevated temperatures. Such "inverse” catalysts are useful for probing electronic interactions at metal-metal compound interfaces and understanding their role in reaction mechanisms. Moreover, the use of a metal substrate is well-suited to vibrational spectrocopy studies using IRAS. Results will be presented for ZrO2/Cu2O/Cu(111) surfaces which probe the synergy of Cu-ZrO2 interfaces for promoting CO2 hydrogenation to methanol. Ambient pressure IRAS and XPS C1s spectra show evidence for surface reaction intermediates including carbonate (CO3*), formate (HCOO*) and HxCO* species, including methoxy which is the surface-bound precursor for methanol. Overall, the results clearly demonstrate the promotional effects of small ZrO2 particles for enhancing the reactivity of Cu surfaces for CO2 hydrogenation. Recent work on the reactivity of other supported clusters will also be presented.
Wednesday
In situ spectroscopy studies of the hydrodeoxygenation of anisole on Ni and Mo oxide catalysts
05:50pm - 06:10pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
The conversion of lignin to transportation fuels is a viable part of the path to reduce reliance on fossil fuels. Oxidized Ni promotes Mo oxide catalysts in the removal of oxygen and the saturation of carbon in lignin. To understand the active state of the catalyst and the role that Ni plays, we have studied the hydrodeoxygenation of a lignin model compound, anisole. Using infrared spectroscopy under reaction conditions, we follow the surface species and link their behavior to the catalyst oxidation state found using ambient pressure X-ray photoelectron spectroscopy. Deuterated anisole studies are key in identifying surface species. We find that the Mo oxidation state is lower when Ni is in the catalyst. Additionally, methoxy groups accumulate on the surface over time.
Wednesday
Methanol decomposition on copper surfaces under ambient conditions: Mechanism, kinetics and structure sensitivity
06:10pm - 06:30pm USA / Canada - Eastern - August 25, 2021 | Room: Zoom Room 27
Roey Ben David, Presenter; Adva Ben Yaacov; Dr. Baran Eren, Weizmann Institute of Science
Division: [CATL] Division of Catalysis Science & Technology
Session Type: Oral - Virtual
Methanol has the potential to become an important energy vector. The so-called "methanol economy" is essentially a carbon-neutral cycle consisting of two groups of reactions: Methanol synthesis from a mixture of CO, CO2, and H2, and methanol-to-hydrogen conversion reaction. Latter includes methanol decomposition (or dry dehydrogenation), partial oxidation, steam reforming, and autothermal reforming. Cu-based materials are currently our best option as catalysts, and they are already used industrially in some of the above-mentioned reactions. This makes the interface between Cu and methanol vapor exceedingly important. Yet, only a handful of experimental mechanistic studies (at the molecular level), under realistic reaction conditions, are available in the literature. Herein, the interaction and decomposition of methanol on different copper surface orientations, Cu(111), Cu(100) and Cu(110), have been studied by means of PM-IRRAS and AP-XPS under 1 mbar methanol pressure in the temperature range of 25-100 °C. Our results reveal that methanol is dissociatively adsorbed on the clean Cu surfaces to form methoxy (CH3O*) and hydrogen at ambient conditions. The temporal evolution of infrared spectra indicates that a transient state of a high-coverage methoxy layer forms immediately after methanol exposure. For achieving an equilibrium coverage, the methoxy excess is eliminated via a further dehydrogenation to CO and its desorption to the gas phase. The kinetics of this process, which involves the activation of C-H bonds, displays a significant structure sensitivity with a much faster kinetics on the corrugated Cu(110) compared to the close-packed surfaces of Cu(111) and Cu(100). We also propose a model that explains the origin of the initial metastable methoxy coverage by considering the previous step of molecular adsorption in the form of H-bonded assemblies.