On the Role of Pd Ensembles in Selective H<sub>2</sub>O<sub>2</sub> Formation on PdAu Alloys

Ham, Hyung Chul; Hwang, Gyeong S.; Han, Jonghee; Nam, Suk Woo; Lim, Tae Hoon

doi:10.1021/jp9043545

Cited by 126 publications

(148 citation statements)

References 19 publications

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“…Pd{111} and Pd{200} facets on AuPd alloy particles, which has been proved to be beneficial for the production of H 2 O 2 in theory, 27 is required. Moreover, the promotional effects of Au on the exposure of Pd active facets and the stabilization of the AuPd alloy nanostructure have been demonstrated.…”

Section: • and Omentioning

confidence: 99%

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Sun

Zhang

Qin

et al. 2015

Environ. Sci. Technol.

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Simultaneous reduction of Cr(VI) to Cr(III) and oxidation of As(III) to As(V) is a promising pretreatment process for the removal of chromium and arsenic from acid aqueous solution. In this work, the synergistic redox conversion of Cr(VI) and As(III) was efficiently achieved in a three-dimensional electrocatalytic reactor with synthesized AuPd/ CNTs particles as electrocatalysts. The AuPd/CNTs facilitated the exposure of active Pd{111} facets and possessed an approximate two-electrontransfer pathway of oxygen reduction with the highly efficient formation of H 2 O 2 as end product, resulting in the electrocatalytic reduction of 97.2 ± 2.4% of Cr(VI) and oxidation of 95.7 ± 4% of As(III). The electrocatalytic reduction of Cr(VI) was significantly accelerated prior to the electrocatalytic oxidation of As(III), and the effectiveness of Cr(VI)/As(III) conversion was favored at increased currents from 20 to 150 mA, decreased initial pH from 7 to 1 and concentrations of Cr(VI) and As(III) ranging from 50 to 1 mg/L. The crucial intermediates of Cr(V) and As(IV) and active free radicals HO• and O 2 •− were found for the first time, whose roles in the control of Cr(VI)/As(III) redox conversion were proposed. Finally, the potential applicability of AuPd/CNTs was revealed by their stability in electrocatalytic conversion over 10 cycles. ■ INTRODUCTIONThe combined pollution of heavy metals in acid wastewater has become a formidable problem to environmental scientists and engineers for decades. As a consequence of improper treatment, effluents containing abundant heavy metal ions such as lead, nickel, copper, arsenic, or chromium may inflow into surface water or seep into groundwater, which pose great threats to aquatic life and drinking water sources.1,2 Thus, it is urgent to remove the heavy metals prior to their discharge into the environment.Arsenic and chromium, as priority pollutants, are highly toxic and frequently coexist with highly acidic wastewater (e.g., acid mine drainage).3 The valence states of arsenic or chromium have decisive impacts on their environmental fate and toxic effect.4,5 For example, As(III) is the most prevalent form of arsenic in the natural environment, which is more toxic than As(V) to mammals. 6 Additionally, As(III) is also more mobile than As(V), because As(III) is quite easier originated from the oxidative weathering or reductive dissolution of As-containing minerals, suggesting the immobilization of As(III) in acid solution more strictly depends on the redox conditions. 7 Therefore, it is advisible to preoxidize As(III) to As(V), coupled with a following adsorption or coprecipitation of the As(V) by using adsorbents or coagulants, to finally enhance the removal of arsenic species in acid aqueous solution. 8,9 Similarly, Cr(VI) is quite soluble and mobile in acid wastewater, 10 whileCr(III) is less toxic and insoluble, and can be effectively immobilized as the hydroxide in a wide pH range. 11,12 Thus, the prereduction of Cr(VI) to Cr(III) is conducive to the complete removal of ch...

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Section: • and Omentioning

confidence: 99%

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Sun

Zhang

Qin

et al. 2015

Environ. Sci. Technol.

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“…Particle size, atomic/surface compositions, the shape and exposed facets of nanocatalysts particles are all the influent factors of catalytic performances of AuPd [15][16][17]. Recently, these isolated Pd atoms within the gold matrix are indentified as the most active catalytic center for vinyl-acetate synthesis and the direct H 2 O 2 synthesis reaction [18][19][20][21]. It is shown that single Pd sites enhanced H 2 O 2 selectivity, whereas surface ensembles of contiguous Pd atoms support H 2 O formation [21].…”

Section: Introductionmentioning

confidence: 99%

“…The exposed facet is one of major factors to determine catalytic properties of Au or AuPd particles. There are several theoretical studies [20,[25][26][27][28][29][30][31][32] of H 2 O 2 synthesis on low index Pd, Au, Pt surfaces or small Au clusters. However, a systematically comparative study of the key elementary reactions for H 2 O 2 and H 2 O formation on these low index Au surfaces, especially Au(111), Au(100) and Au(110) and stepped Au surfaces, is very necessary.…”

Section: Introductionmentioning

confidence: 99%

Brønsted–Evans–Polanyi Relations for H2O2 Synthesis on Gold Surfaces

Wang

2012

Catal Lett

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By means of density functional theory calculations, the reaction mechanisms of H 2 O 2 synthesis on three low index and two stepped Au surfaces have been investigated in detail. This study shows the activation energies of five elementary reaction steps of H 2 O 2 synthesis, which include two hydrogenation and three decomposition steps of key species, are a function of reaction energies, which observe the Brønsted-EvansPolanyi rules on both the flat Au surfaces and the step edge sites of stepped Au surfaces. This study not only provides a simple method to estimate the reaction barriers of elementary steps of H 2 O 2 synthesis by the reaction energies but also predicts the catalytic performances of Au nanoparticles applied in real catalysis.

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“…Theoretical computational methods provide a useful complement to experiments for the understanding of the adsorption of hydrogen on palladium [9-12 and references therein], platinum [13-16 and references therein], and bimetallic Pd-Ag [17][18][19][20][21] and Pd-Au [22,23] surfaces. This wealth of computational studies is contrasted by a small amount of theoretical publications in which the presence of a support was taken into account [24][25][26][27][28].…”

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confidence: 99%

Computational study of the adsorption of molecular hydrogen on PdAg, PdAu, PtAg, and PtAu dimers

Matczak

2010

Reac Kinet Mech Cat

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The adsorption and dissociation of the H 2 molecule on the PdAg, PdAu, PtAg, and PtAu heteronuclear dimers, both isolated and deposited on carbon, were investigated by means of density functional theory. It was found that the Pd and Pt ends of the isolated dimers adsorb H 2 more exoenergetically than the Ag and Au ends. The dimers were also deposited on a carbon support and it turned out that they prefer to adsorb on the support by their Pd and Pt ends rather than by the Ag and Au ends. The adsorption of H 2 on the carbon-supported dimers is somewhat less exoenergetic than that on the isolated dimers but, after the dissociation of H 2 , the binding of the H atoms to the dimers remains stronger in the presence of the support.

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On the Role of Pd Ensembles in Selective H₂O₂ Formation on PdAu Alloys

Cited by 126 publications

References 19 publications

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Brønsted–Evans–Polanyi Relations for H2O2 Synthesis on Gold Surfaces

Computational study of the adsorption of molecular hydrogen on PdAg, PdAu, PtAg, and PtAu dimers

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On the Role of Pd Ensembles in Selective H2O2 Formation on PdAu Alloys

Cited by 126 publications

References 19 publications

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution

Brønsted–Evans–Polanyi Relations for H2O2 Synthesis on Gold Surfaces

Computational study of the adsorption of molecular hydrogen on PdAg, PdAu, PtAg, and PtAu dimers

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On the Role of Pd Ensembles in Selective H₂O₂ Formation on PdAu Alloys