Identification of single-site gold catalysis in acetylene hydrochlorination

Malta, Grazia; Kondrat, Simon A.; Freakley, Simon J.; Davies, Catherine; Li, Lu; Dawson, Simon R.; Thetford, Adam; Gibson, Emma K.; Morgan, David; Jones, Wilm; Wells, Peter P.; Johnston, Peter; Catlow, C. Richard A.; Kiely, Christopher J.; Hutchings, Graham J.

doi:10.1126/science.aal3439

Cited by 417 publications

(444 citation statements)

References 43 publications

(41 reference statements)

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“…Monitoring the changes in white line height, a feature detectable in the XANES region which corresponds to the Au 2p 3/2 → 5d primary transition (see experimental section for more details), showed that while heating the catalyst to the reaction temperature (200°C) under Ar, the Au(III)/Au(I) ratio significantly changed from Au(III) chloride to Au(I) chloride (Figure 1b). 9 Therefore, while it is true to state single-site cationic species are retained on…”

Section: ■ Introductionmentioning

confidence: 99%

“…9 Analysis of the Au L 3 -edge X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) showed the operating catalyst comprised of atomically dispersed cationic species with no Au nanoparticles being present in the most active Au/C catalysts. During the reaction, distinct changes in the XANES were observed, which clearly correlated to the catalyst productivity, showing that the active catalysts were comprised of atomically dispersed cationic gold in both Au(III) and Au(I) oxidation states.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Highly active Au/C catalysts prepared by the impregnation of Au from a solution of aqua regia have previously been shown to consist of atomically dispersed cationic Au and be highly active for acetylene hydrochlorination. 9 To test the thermal stability of highly dispersed Au species, the catalyst was heated to 350°C (at a rate of 5°C/min) under an inert N 2 atmosphere (to prevent the combustion of the carbon support) while being characterized using in situ XRD (Figure 1a). Given that the single-site cationic Au species, shown by XANES analysis 9 to be present in catalyst, are undetectable by XRD, no diffraction peaks from Au were observed at room temperature.…”

Section: ■ Introductionmentioning

confidence: 99%

“…9 To test the thermal stability of highly dispersed Au species, the catalyst was heated to 350°C (at a rate of 5°C/min) under an inert N 2 atmosphere (to prevent the combustion of the carbon support) while being characterized using in situ XRD (Figure 1a). Given that the single-site cationic Au species, shown by XANES analysis 9 to be present in catalyst, are undetectable by XRD, no diffraction peaks from Au were observed at room temperature. The dispersed Au(III)/Au(I) species in the 1 wt % Au/C (1% Au/C-AR) catalyst showed high thermal stability from ambient temperature up to 250°C, with no characteristic reflections of fcc Au being observed over this temperature range.…”

Section: ■ Introductionmentioning

confidence: 99%

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Deactivation of a Single-Site Gold-on-Carbon Acetylene Hydrochlorination Catalyst: An X-ray Absorption and Inelastic Neutron Scattering Study

et al. 2018

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Single-site Au species supported on carbon have been shown to be the active sites for acetylene hydrochlorination. The evolution of these single-site species has been monitored by Au L 3 X-ray absorption spectroscopy (XAS). Alternating between a standard reaction mixture of HCl/C 2 H 2 and the single reactants has provided insights into the reaction mechanism and catalyst deactivation processes. We demonstrate that oxidative addition of HCl across an Au(I) chloride species requires concerted addition with C 2 H 2 , in accordance with both the XAS measurements of Au oxidation state and the reaction kinetics being first order with respect to each reactant. Excess C 2 H 2 changes the Au speciation and results in the formation of oligomeric acetylene species which were detected by inelastic neutron scattering. Catalyst deactivation at extended reaction times can be correlated with the formation of metallic Au particles. These Au(0) species generated during the sequential gas experiments, or after prolonged reaction times, results in the analysis of the normalized near-edge white line intensity becoming an unsuitable guide for identifying the active Au species, affecting the strong correlation between normalized white line height and VCM productivity usually observed in the active catalyst. Thus, a combination of scanning transmission electron continued...

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Deactivation of a Single-Site Gold-on-Carbon Acetylene Hydrochlorination Catalyst: An X-ray Absorption and Inelastic Neutron Scattering Study

et al. 2018

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“…We have previously highlighted the work of LezcanoGonzalez et al (2016), which combines high-resolution fluorescence-detection X-ray absorption near-edge spectroscopy, X-ray diffraction and X-ray emission spectroscopy under operando conditions to provide detailed new insights into the nature of the Mo species on zeolite ZSM-5 during methane dehydroaromatization. Another recent example is the work of Malta et al (2017), who combined XAFS and modelling to show that in an industrially important acetylene hydrochlorination catalyst, comprising gold on a carbon support, the active sites are not, as previously thought, gold nanoclusters but single gold ions. Catalysis will unquestionably continue to pose fascinating problems for structural science.…”

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Developments in the structural science of materials

Catlow

2017

Int Union Crystallogr J

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The papers published during the last year in IUCrJ in the fields of materials and computational science illustrate well the challenges posed by structural problems in the science of materials and the key role that computation can play in this and related fields in structural science. As in previous years, they demonstrate the continuing developments in techniques and instrumentation and the increasingly complex structural problems which these developments now make accessible; the role of computation in interpreting and predicting structures is equally clear.An excellent example of technical developments facilitating new structural science is provided by the article of Meng & Zuo (2016), which probes three-dimensional nanostructures using a technique that employs high-resolution and low-dose scanning electron nano-diffraction (SEND) to acquire three-dimensional diffraction patterns. Their work investigates TiN -a material that is widely used in the electronics industry -and Fig. 1 illustrates how they were able to reconstruct grain structures within the material. Detailed knowledge of this microstructure is essential in understanding and optimizing the properties of the material Previous editorials have emphasized the key role of diffuse scattering, which is also facilitated by technical advances. The importance of the field in materials science is well illustrated by the article of Sawa (2016), which highlights the work of Welberry & Goossens (2016) on the interpretation of diffuse scattering from the high-temperature superconductor, HgBa 2 CuO 4 + . Analysis of the diffuse scattering data reveals fascinating features involving the displacement of metal atoms around oxygen interstitial chains. This article along with several others demonstrates the need to elucidate complex structural features in disordered materials.Analysis of diffuse scattering is also vital in the particularly exciting challenge of developing detailed models for the atomic arrangements in quasicrystals. The article of Ishimasa (2016) highlights the study of Yamada et al. (2016) on the atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal, which employs synchrotron-based diffraction and diffuse scattering to investigate this difficult problem.The complexity of structural problem that can now be addressed is well illustrated in the paper of Rozhdestvenskaya et al. (2017), who use a wide range of techniques including several electron crystallographic methods, XRPD and modelling to solve the structure of denisovite, a highly complex, fibrous, polytypical silicate. The structure revealed is shown in Fig. 2. The article is an elegant illustration of the capacity of, and the need for, a multi-technique approach in addressing structural problems in materials science, A further example of complex structural science is given by the study of SnTe reported by Sist et al. (2016). This material is increasingly investigated owing to its potential as a thermoelectric material and as a topological insulator. Their study again reveals the im...

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