Microstructure studies in nanoporous Au: Effects on electro-oxidation

Lakshmanan, C.; Behera, Anil Kumar; Viswanath, R. N.; Amirthapandian, S.; Rajaraman, R.; Amarendra, G.

doi:10.1016/j.scriptamat.2017.11.018

Cited by 8 publications

(6 citation statements)

References 13 publications

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“…5 and Movie S1). Immediately after O3 treatment, the surface was covered with silver-rich oxides, consistent with previous work [10,39]. When O2 (0.1 Torr) and CH3OH (0.05 Torr) were introduced into the microscope, metallic nanoparticles rapidly formed on the surface under exposure to the electron beam.…”

Section: Environmental Transmission Electron Microscopy (E Tem)supporting

confidence: 88%

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Zugic

Spronsen

Heine

et al. 2019

Journal of Catalysis

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Activating pretreatments are used to tune surface composition and structure of bimetallic-alloy catalysts. Herein, the activation-induced changes in material properties of a nanoporous Ag0.03Au0.97 alloy and their subsequent evolution under steady-state CH3OH oxidation conditions are investigated. Activation using O3 results in AgO and Au2O3, strongly enriching the near-surface region in Ag. These oxides reduce in the O2/CH3OH mixture, yielding CO2 and producing a highly Ag-enriched surface alloy. At the reaction temperature (423 K), Ag realloys gradually with Au but remains enriched (stabilized by surface O) in the top few nanometers, producing methyl formate selectively without significant deactivation. At higher temperatures, bulk diffusion induces sintering and Ag redistribution, leading to a loss of activity. These findings demonstrate that material properties determining catalytic activity are dynamic and that metastable (kinetically trapped) forms of the material may be responsible for catalysis, providing guiding principles concerning the activation of heterogeneous catalysts for selective oxidation. KeywordsNanoporous Au; diluted alloys; selective oxidation of CH3OH; in situ/operando multimodal approach; metastability surface composition and structure of alloy catalysts determine the reactivity as well as selectivity because of intrinsic differences in bonding and bond activation of different metals. Furthermore, at modest reaction temperatures, the stable surface structure is not necessarily the thermodynamic ground state but can be a metastable one that is kinetically trapped. Hence, there is an opportunity to design selective catalytic processes that exploit these metastable states and thus to develop principles that predict how to tune the surface composition and structure using specific activation procedures and steady-state conditions-reaction temperature, pressure, and the ratio of reactants.Advances in microscopy [1-3] and spectroscopy [4] have enabled the direct interrogation of atomic-scale surface arrangements under functioning catalytic conditions. Such data provide critical input for the rational design of improved catalytic materials. The importance of this concept has recently been illustrated for several catalytic systems, including Cu-ZnO, and . A recent study followed the shape of Au nanoparticles in situ at an O2 pressure of 1 bar using TEM showing a shape transition from truncated octahedral to rounded upon cooling below 393 K, explained by the O2(ads)-induced stabilization of the (110) facet [9].Recently, structural and compositional rearrangements induced during the initial activation, i.e. oxidation with O3, and the subsequent reduction of nanoporous (np) Ag0.03Au0.97 was demonstrated [10]. Nanoporous Ag0.03Au0.97 is a support-free Au alloy with small amounts of Ag, produced by selectively etching Ag from a Ag-rich AgAu alloy. After O3 treatment, both Au and Ag are oxidized, forming a thin film of Au2O3 and AgO (Fig. 1). The surface also becomes substantially enriched in Ag, by ~3...

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Section: Environmental Transmission Electron Microscopy (E Tem)supporting

confidence: 88%

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Zugic

Spronsen

Heine

et al. 2019

Journal of Catalysis

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“…The results obtained from the computational work claimed that SFT defects are energetically more favorable in metal ligaments and grow via a vacancy aggregation mechanism [17]. These observations were consistent with our earlier results of the formation of SFT defects, size of 2-3 nm, in the Au ligaments through electrochemical measurements combined with high-resolution transmission electron microscopy (HRTEM) [18]. Fu et al [19] found that SFTs are formed when np-Au foams are irradiated at high dose rate.…”

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confidence: 90%

“…Our earlier positron annihilation Doppler broadening S-parameter studies on nanoporous Au suggested that the vacancy-type defects that are responsible for the mechanical properties are localized along the ligaments [21]. However, due to the lack of direct atomistic observations under computer simulations and experimental data, the correlation between defects structure and mechanical properties which characterize the nanoporous metals [18] is not yet fully ascertained and is currently a topic of rigorous investigations. In this work, we study the as-dealloyed and Fe + ion irradiated np-Au with temperature annealing using positron annihilation Doppler broadening and nano-indentation techniques.…”

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Vacancy defects and their influence on mechanical properties in as-dealloyed and Fe⁺ ion irradiated nanoporous Au

Lakshmanan

Viswanath

Panda

et al. 2020

EPL

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Continuous depth sensing nano-indentation hardness measurements coupled with low-energy positron beam Doppler broadening line shape measurements were performed to investigate the influence of vacancy defects on mechanical properties in as-dealloyed and Fe+ ion irradiated nanoporous Au. A linear relationship has been obtained from the actual data between the nano-indentation hardness and square root of the concentration of defects. It suggests that the vacancy-type defects that evolved in the ligaments play a significant role in the modification of mechanical properties in both as-dealloyed and Fe+ ion irradiated nanoporous Au. The results have been also compared with those obtained on bulk Au.

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“…These values are consistent with the reported results. 30,31 Hence, the analyses of Figs. 2a-2d confirm that the designed Au NP/V 2 O 5 structure is indeed employed in the studied sensor device.…”

Section: Resultsmentioning

confidence: 99%

Study of a Formaldehyde Gas Sensor Based on a Sputtered Vanadium Pentoxide Thin Film Decorated with Gold Nanoparticles

Niu

Liu²,

Pan

et al. 2021

ECS J. Solid State Sci. Technol.

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Formaldehyde (HCHO) gas sensing properties of a new sensor based on a sputtered vanadium pentoxide (V 2 O 5 ) thin film decorated with evaporated gold (Au) nanoparticles (NPs) are studied and reported herein. The use of Au NPs effectively increases the surface area/volume (S A /V) ratio and enhances the catalytic activity of Au metal. Experimentally, good p-type sensing characteristics, including a high sensing response ratio of 73.1% under 20 ppm HCHO/air gas and a small recovery time of 6.8 s at 225 °C, are obtained. An extremely low detecting level of 15 ppb HCHO/air is also acquired. Due to these advantages and the benefits of simple structure and easy fabrication, the studied Au NP/V 2 O 5 device is an excellent candidate for p-type consumption formaldehyde gas sensing and complementary metal oxide sensor array (CMOSA) applications.

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Microstructure studies in nanoporous Au: Effects on electro-oxidation

Cited by 8 publications

References 13 publications

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Vacancy defects and their influence on mechanical properties in as-dealloyed and Fe⁺ ion irradiated nanoporous Au

Study of a Formaldehyde Gas Sensor Based on a Sputtered Vanadium Pentoxide Thin Film Decorated with Gold Nanoparticles

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Microstructure studies in nanoporous Au: Effects on electro-oxidation

Cited by 8 publications

References 13 publications

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag0.03Au0.97

Vacancy defects and their influence on mechanical properties in as-dealloyed and Fe+ ion irradiated nanoporous Au

Study of a Formaldehyde Gas Sensor Based on a Sputtered Vanadium Pentoxide Thin Film Decorated with Gold Nanoparticles

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Vacancy defects and their influence on mechanical properties in as-dealloyed and Fe⁺ ion irradiated nanoporous Au