Ensemble Effects in the Oxygen/Chlorine/Pd(100) System

Klier, K.; Simmons, G.W.; Park, Kenneth T.; Wang, Yarw-Nan; Hess, James S.; Herman, R.G.

doi:10.1021/la970442x

Cited by 4 publications

(42 citation statements)

References 50 publications

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“…In general, the diffusion of adsorbates on metal surfaces is a facile process so that coadsorbed Cl can dynamically react when the surface composition is changed. This scenario is observed for instance with the diffusion and segregation behavior of a O/Cl coadsorbate on a Pd(100) surface 9 or the dynamic catalytic response of a Cl-precovered Pd(110) surface, thereby modifying the selectivity in dichloroethylene oxidation to CO or CO 2 . 10 Compound formation between the catalyst and the poisoning species has been largely ignored.…”

Section: Introductionmentioning

confidence: 99%

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Hofmann

Zweidinger

Seitsonen

et al. 2010

Phys. Chem. Chem. Phys.

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The dynamic behavior of surface accommodated chlorine atoms on RuO(2)(110) was studied by a variety of experimental methods including high resolution core level shift, thermal desorption-, and in situ infrared spectroscopy as well as in situ surface X-ray diffraction in combination with state-of-the-art density functional theory calculations. On the chlorinated RuO(2)(110) surface the undercoordinated oxygen atoms have been selectively replaced by chlorine. These strongly bound surface chlorine atoms shift from bridging to on-top sites when the sample is annealed in oxygen, while the reverse shift of Cl from on-top into bridge positions is observed during CO exposure; the vacant bridge position is then occupied by either chlorine or CO. For the CO oxidation reaction over chlorinated RuO(2)(110), the reactant induced site switching of chlorine causes a site-blocking of the catalytically active one-fold coordinatively unsaturated (1f-cus) Ru sites. This site blocking reduces the number of active sites and, even more important, on-top Cl blocks the free migration of the adsorbed reactants along the one-dimensional 1f-cus Ru rows, thus leading to a loss of catalytic activity.

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Section: Introductionmentioning

confidence: 99%

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Hofmann

Zweidinger

Seitsonen

et al. 2010

Phys. Chem. Chem. Phys.

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“…Nesse caso o cloreto produz o bloqueio dos sítios metálicos resultando na diminuição da acessibilidade dos reagentes a esses sítios 11,12 . ii) A outra interpretação é considerar o envenenamento do cloreto como um efeito eletrônico.…”

Section: Introductionunclassified

“…A influência do cloreto na atividade catalítica pode ser interpretada de duas formas: i) Como um efeito estérico, onde o haleto coordena-se aos sítios que são necessários a adsorção e ativação de outras espécies [9][10][11] . Nesse caso o cloreto produz o bloqueio dos sítios metálicos resultando na diminuição da acessibilidade dos reagentes a esses sítios 11,12 .…”

Section: Introductionunclassified

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Cunha¹,

Faccin²,

Moro³

et al. 2002

Quím. Nova

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Recebido em 24/4/01; aceito em 4/9/01 INFRARED AND X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF CHLORIDE EFFECT IN PALLADIUM CATALYSTS. Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bonded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d 5/2 binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al 2 O 3 reduced at 500 o C, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.Keywords: chloride poisoning effect; infrared; XPS. INTRODUÇÃOAs propriedades catalíticas de catalisadores metálicos suportados são geralmente influenciadas pela presença de aditivos, que podem ser tanto promotores 1,2 como também inibidores [3][4][5][6] . Alguns inibidores como cloreto, as vezes, podem estar presente no catalisador, não como aditivos, mas sim, como resíduo dos sais metálicos precursores do catalisador, e podem produzir a diminuição na atividade catalítica 3,7,8 .A influência do cloreto na atividade catalítica pode ser interpretada de duas formas: i) Como um efeito estérico, onde o haleto coordena-se aos sítios que são necessários a adsorção e ativação de outras espécies 9-11 . Nesse caso o cloreto produz o bloqueio dos sítios metálicos resultando na diminuição da acessibilidade dos reagentes a esses sítios 11,12 . ii) A outra interpretação é considerar o envenenamento do cloreto como um efeito eletrônico. Nesse caso cloreto metálico pode ser formado 13,14 . Para metais nobres como paládio, esses haletos são mais estáveis que os óxidos 13,15 . A atividade catalítica portanto diminui, pois os haletos metálicos são menos ativos que as partículas metálicas.Nesse trabalho, nossos resultados evidenciam que a presença de cloreto no catalisador metálico produz efeitos eletrônicos e que quando esse é reduzido a temperatura de 500 o C, a interação do paládio disperso com o oxigênio do suporte alumina pode também resultar em um efeito semelhante ao do cloreto. Uma redução parcial do efeito do envenenamento por cloreto pode ser obtida quando usa-se molibdênio/alumina como suporte. As interpretações foram feitas a partir da análise através da espectroscopia de fotoelétrons excitados por raios-X e também na análise das ligações por retro-doação pi entre o metal e a carbonila, que dependem da densidade eletrônica do metal. Essas ligações podem ser monitoradas a partir da espectroscopia no infravermelho. PARTE EXPERIMENTAL Síntese do Pd/Al 2 O 3 (sem cloreto)O su...

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“…The control sample (Sample 4) was prepared with η-Al 2 O 3 by condensing TCE onto 1.00 g of support, respectively) while the ampule was at 77 K. After loading, the samples were immediately sealed. A reference sample of 13 C-TCE in deuterated ethanol was also prepared (10% 13 C 2 -TCE, 90% CD 3 CD 2 OH).…”

Section: Introductionmentioning

confidence: 99%

“…NMR Experiments. 13 C NMR spectra were obtained using a home-built singly tuned NMR probe with a Chemagnetics 400 MHz spectrometer equipped with a Janis STVP-200 dewar. The spinecho pulse sequence was used with a typical 13 C π pulse length of 5.0 µs.…”

Section: Introductionmentioning

confidence: 99%

Reductive Hydrodechlorination of Trichloroethylene by Palladium-on-Alumina Catalyst: ¹³C Solid-State NMR Study of Surface Reaction Precursors

2006

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Adsorption of trichloroethylene (TCE) on alumina-supported palladium catalysts (Pd/Al2O3) was studied in the presence and absence of hydrogen using 13C-solid state NMR. Carbon-13 NMR spectra indicate that at low coverage strongly adsorbed species are formed while at high coverage additional physisorbed species are present. Carbon-13 spin-echo amplitude data measured as a function of pulse separation, tau, was used to determine the 13C-13C intramolecular dipolar coupling and the carbon-carbon bond length of adsorbed species. Results indicate that a substantial fraction of the chemisorbed carbon species had undergone carbon-carbon bond scission forming single-carbon fragments, suggesting that the activation energy for carbon-carbon bond scission is comparable to the heat of adsorption. For the remaining surface species, the double bond is elongated to 1.46 +/- 0.03 A and is suspected to be chemically bonded ethynyl. At room temperature, adding an excess of hydrogen to catalyst that is covered to saturation with TCE precursors produces only in a small amount of ethane, indicating the fraction of surface species that are hydrodehalogenation precursors is small.

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Ensemble Effects in the Oxygen/Chlorine/Pd(100) System

Cited by 4 publications

References 50 publications

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Reductive Hydrodechlorination of Trichloroethylene by Palladium-on-Alumina Catalyst: ¹³C Solid-State NMR Study of Surface Reaction Precursors

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Ensemble Effects in the Oxygen/Chlorine/Pd(100) System

Cited by 4 publications

References 50 publications

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Reductive Hydrodechlorination of Trichloroethylene by Palladium-on-Alumina Catalyst: 13C Solid-State NMR Study of Surface Reaction Precursors

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Reductive Hydrodechlorination of Trichloroethylene by Palladium-on-Alumina Catalyst: ¹³C Solid-State NMR Study of Surface Reaction Precursors