Surface Modifications during a Catalytic Reaction: a Combined APT and FIB/SEM Analysis of Surface Segregation

Barroo, Cédric; Janvelyan, Nare; Zugic, Branko; Magyar, Andrew A.P.; Akey, Austin; Biener, Juergen; Friend, Cynthia M.; Bell, David C.

doi:10.1017/s1431927616002634

Cited by 4 publications

(6 citation statements)

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“…Due to the lower free surface energy and molar heat of sublimation of Ag compared to Au, Ag atoms in a solid solution of Ag–Au alloy are expected to preferentially diffuse and concentrate at the surface. Several studies have verified Ag surface segregation in Ag–Au systems under ultra-high vacuum (UHV) conditions [ 43 , 44 , 45 , 46 ] and under various oxidative atmospheres [ 47 , 48 , 49 , 50 ]. A recent APT investigation of surface segregation in Ag–Au alloys at elevated temperatures (323 K < T < 673 K) indicated that under an unreactive atmosphere, such as Ar (6 kPa), Ag segregation is negligible for short treatment duration (1 h) [ 42 ].…”

Section: Resultsmentioning

confidence: 99%

Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography

2021

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Surface chemistry information is crucial in understanding catalytic and sensing mechanisms. However, resolving the outermost monolayer composition of metallic nanoporous materials is challenging due to the high tortuosity of their morphology. In this study, we first elaborate on the capabilities and limitations of atom probe tomography (APT) in resolving interfaces. Subsequently, an electrochemical approach is designed to characterize the surface composition of nanoporous gold (NPG), developed from dealloying an inexpensive precursor (95 at. % Ag, 5 at. % Au), by the means of aqueous electrochemical measurements of the selective electrosorption of sulfide ions, which react strongly with Ag, but to a significantly lesser extent with Au. Accordingly, cyclic voltammetry was performed at various scan rates on NPG in alkaline aqueous solutions (0.2 M NaOH; pH 13) in the presence and absence of 1 mM Na2S. Calibrations via similar voltammetric measurements on pure polycrystalline Ag and Au surfaces allowed for a quantitative estimation for the Ag surface coverage of NPG. The sensitivity threshold for the detection of the adsorbate–Ag interaction was assessed to be approximately 2% Ag surface coverage. As curves measured on NPG only showed featureless capacitive currents, no faradaic charge density associated with sulfide electrosorption could be detected. This study opens a new avenue to gain further insight into the monolayer surface coverage of metallic nanoporous materials and assists in enhancement of the interpretation of APT reconstructions.

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Section: Resultsmentioning

confidence: 99%

Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography

2021

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“…The authors also mentioned that Pt deposition precursors do not allow for stable APT experiments under voltage-pulse mode. Further work proved that Pt-based precursor as a filling material allows for npAu analysis by APT in laser pulse mode [173][174], emphasizing the importance of acquisition parameters. The second set of experiments uses an alternative procedure to fill the pores by electrodeposition [175,176].…”

Section: Catalysts As Porous Materials-nanoporous Aumentioning

confidence: 97%

Atom Probe Tomography for Catalysis Applications: A Review

2019

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Atom probe tomography is a well-established analytical instrument for imaging the 3D structure and composition of materials with high mass resolution, sub-nanometer spatial resolution and ppm elemental sensitivity. Thanks to recent hardware developments in Atom Probe Tomography (APT), combined with progress on site-specific focused ion beam (FIB)-based sample preparation methods and improved data treatment software, complex materials can now be routinely investigated. From model samples to complex, usable porous structures, there is currently a growing interest in the analysis of catalytic materials. APT is able to probe the end state of atomic-scale processes, providing information needed to improve the synthesis of catalysts and to unravel structure/composition/reactivity relationships. This review focuses on the study of catalytic materials with increasing complexity (tip-sample, unsupported and supported nanoparticles, powders, self-supported catalysts and zeolites), as well as sample preparation methods developed to obtain suitable specimens for APT experiments.

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“…npAu is a Au-rich AuAg alloy where the residual Ag reflects the dealloying process is never 100% complete (Figure 5d). 63 The same dealloying process can be applied to many other alloy systems, including Ag-free npAu prepared by dealloying AuAl starting alloys, 64 npCu generated from CuMn, 50 CuAl 65 , and CuZn 52 alloys, and npAg prepared from AgAl alloys. 66 While dealloying single-phase starting alloys generally generates a unimodal nanometer-scale pore size distribution, more complex, hierarchical pore size distributions can be obtained by dealloying multiphase starting alloys such as the two-phase Al-CuAl 2 eutectic alloy (Figure 5f).…”

Section: Support-free Nanoporous Alloysmentioning

confidence: 99%

“…Selected Reactions Reported on Au-, Ag-, and Cu-Based Dilute Alloys Reviewed in Section 3 good candidates for catalytic studies. Minority alloy components can be present as residual from the selective corrosion dealloying process 63 or introduced after dealloying by various methods. 47,60,69,70 For example, npAu prepared by dealloying a AuAg alloy showed low-temperature CO oxidation activities similar to those of supported Au, without the contribution of Au-oxide interfaces.…”

Section: Oxidation Reactions On Au-based Materialsmentioning

confidence: 99%

“…The classical example for a monolithic nanoporous metal made by dealloying is npAu prepared by selective corrosion dealloying of Ag from Au 1– x Ag x alloys ( x = 0.65–0.75). npAu is a Au-rich AuAg alloy where the residual Ag reflects the dealloying process is never 100% complete (Figure d) . The same dealloying process can be applied to many other alloy systems, including Ag-free npAu prepared by dealloying AuAl starting alloys, npCu generated from CuMn, CuAl, and CuZn alloys, and npAg prepared from AgAl alloys .…”

Section: Advanced Materialsmentioning

confidence: 99%

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Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

et al. 2022

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The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalystsin which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivityare particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle “raspberry colloid templated (RCT)” materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

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Surface Modifications during a Catalytic Reaction: a Combined APT and FIB/SEM Analysis of Surface Segregation

Cited by 4 publications

References 1 publication

Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography

Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography

Atom Probe Tomography for Catalysis Applications: A Review

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

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