Pd/Cu alloys as hydrodechlorination catalysts: a medium-energy ion scattering study of surface composition under exposure to chlorinated hydrocarbons

Noakes, T.C.Q.; Bailey, Paul; Laroze, S.C.; Bloxham, L.H.; Raval, Rasmita; Baddeley, Christopher J.

doi:10.1002/1096-9918(200008)30:1<81::aid-sia762>3.0.co;2-2

Cited by 22 publications

(18 citation statements)

References 14 publications

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“…Both surfaces contained a mixture of oxidized Pt and Rh species, however the amount of surface Rh oxide was directly related to its nominal content. 71 Tenney and coworkers investigated Pt-Au 73 and Ni-Au 72 nanoparticles supported on TiO 2 (110). They found that under Langmuir CO exposure, segregation of Ni and Pt on the surface occurred, whereas under UHV, Au is preferentially segregated over Pt and Ni.…”

Section: 22mentioning

confidence: 99%

“…This indicates that both hydrocarbon and hydrogen would induce Pd segregation in Pd catalysts when alloyed with more noble elements like Cu, Ag or Au. On the other hand, if the organic molecule contains more electronegative functional groups, the situation may be reversed, as suggested by the adsorption of trichloroethylene over the same Pd 0.5 Cu 0.5 (110) single crystal. In this case, Cu enrichment in the first surface layer was shown by MEIS.…”

Section: Hydrogenation Reactionsmentioning

confidence: 99%

“…Applying medium-energy ion scattering (MEIS), the effect of organic component on segregation has been explored. [110][111][112] Noakes et al 110 used a Pd 0.5 Cu 0.5 (110) single crystal, which was slightly Pd-rich under the initial preparation condition. Adsorbing ethylene at 468 K gave rise to substantial Pd segregation.…”

Section: Hydrogenation Reactionsmentioning

confidence: 99%

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Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

Zafeiratos

Piccinin

Teschner

2012

Catal. Sci. Technol.

212

182

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Alloys play a crucial role in several heterogeneous catalytic processes, and their applications are expected to rise rapidly. This is essentially related to the vast number of configurations and type of surface sites that multi-component materials can afford. It is well established that the chemical composition at the surface of an alloy usually differs from that in the bulk. This phenomenon, referred to as surface segregation, is largely controlled by the surface free energy. However, surface energy alone cannot safely predict the active surface state of a solid catalyst, since the contribution of other parameters such as size and support effects, as well as influence of the adsorbates, play a major role. This can lead to numerous surface configurations as for example over the length of a catalytic reactor, as the chemical potential of the gas phase changes continuously over the catalyst bed and hence different reactions may prevail at different catalyst bed segments. Thanks to the rapid improvement of the analytical surface science characterization techniques and theoretical methodologies, the potential effects induced by alloyed catalysts are better understood. For catalysis, the relevance of measurements performed on well-defined surfaces under idealized ultrahigh vacuum conditions has been questioned and studies in environments that closely resemble conditions of working alloy catalysts are needed. In this review we focus on experimental and theoretical studies related to in situ (operando) observations of surface segregation and phase separation phenomena taking place on the outermost surface layers of alloy catalysts. The combination of first principles theoretical treatment and in situ observation opens up new perspectives of designing alloy catalysts with tailored properties

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Section: 22mentioning

confidence: 99%

Section: Hydrogenation Reactionsmentioning

confidence: 99%

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Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

Zafeiratos

Piccinin

Teschner

2012

Catal. Sci. Technol.

212

182

View full text Add to dashboard Cite

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“…Segregation of Pd 0.5 Cu 0.5 (110) single crystal in UHV was studied 79 using a medium-energy ion scattering, a surface analytical technique with the unique ability to provide information on surface composition with depth resolution at the level of atomic layer for crystalline materials. Adsorption of hydrocarbons or hydrogen induces Pd segregation in Pd catalysts significantly when alloyed with elements like Cu, Ag or Au.…”

Section: Pd-cumentioning

confidence: 99%

“…For example, upon adsorption of trichloroethene, Cu is segregated and the first three layers become rich in Cu due to the relatively electropositive 3d metal compared to Pd. 79 A similar behavior of restructuring was observed on Pd x Cu 1Àx nanoparticles supported on zeolite. The structure and chemistry of Pd x Cu 1Àx bimetallic nanoparticles were explored by using XANES and FTIR under reaction conditions of CO hydrogenation.…”

Section: Pd-cumentioning

confidence: 99%

Synthesis, catalysis, surface chemistry and structure of bimetallic nanocatalysts

2012

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Bimetallic catalysts are one of the main categories of metal catalysts due to the tunability of electronic and geometric structures through alloying a second metal. The integration of a second metal creates a vast number of possibilities for varying the surface structure and composition of metal catalysts toward designing new catalysts. It is well acknowledged that the surface composition, atomic arrangement, and electronic state of bimetallic catalysts could be different from those before a chemical reaction or catalysis based on ex situ studies. Thanks to advances in electron-based surface analytical techniques, the surface chemistry and structure of bimetallic nanoparticles can be characterized under reaction conditions and during catalysis using ambient pressure analytical techniques including ambient pressure XPS, ambient pressure STM, X-ray absorption spectroscopy and others. These ambient pressure studies revealed various restructurings in the composition and arrangement of atoms in the surface region of catalysts under reaction conditions or during catalysis compared to that before reaction. These restructurings are driven by thermodynamic and kinetic factors. The surface energy of the constituent metals and adsorption energy of reactant molecules or dissociated species on a metal component are two main factors from the point of view of thermodynamics. Correlations between the authentic surface structure and chemistry of catalysts during catalysis and simultaneous catalytic performance were built for understanding catalytic mechanisms of bimetallic catalysts toward designing new catalysts with high activity, selectivity, and durability.

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Catalytic chemistry of chloro- and chlorofluorocarbon dehalogenation: from macroscopic observations to molecular level understanding

Kovalchuk

d’Itri

2004

Applied Catalysis A: General

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Pd/Cu alloys as hydrodechlorination catalysts: a medium-energy ion scattering study of surface composition under exposure to chlorinated hydrocarbons

Cited by 22 publications

References 14 publications

Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

Synthesis, catalysis, surface chemistry and structure of bimetallic nanocatalysts

Catalytic chemistry of chloro- and chlorofluorocarbon dehalogenation: from macroscopic observations to molecular level understanding

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