The influence of electronic structure on D2 activated dissociative chemisorption at Cu85Pd15{110}

Cottrell, C.; Bowker, Michael; Hodgson, A.; Worthy, G.

doi:10.1016/0039-6028(94)00736-5

Cited by 13 publications

(9 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus if S 0 (E Ќ ) is measured at a constant nozzle temperature by increasing i , the values obtained will be larger than obtained at the same normal energy by dropping the nozzle temperature, since the latter decreases the population of vibrationally excited molecules in the beam. This is the behavior observed on Cu, 13,25 Ag, 14 and the (2ϫ1) Cu 85 Pd 15 (110) 26 surfaces, where vibrationally excited states dominate sticking and S 0 (E Ќ ) curves obtained for a constant nozzle temperature, by increasing i , drop slowly by comparison with the normal incidence curve. Sticking probabilities on the ) alloy were measured as a function of incidence angle at various fixed nozzle temperatures, in order to investigate the role of vibrational energy and the energy scaling relationship.…”

Section: Dissociation On (ͱ3؋ͱ3)r30°sn/pt(111)mentioning

confidence: 58%

“…However, this function does not give satisfactory fits to the data from the ) alloy, which shows an exponential increase in S(E) followed by a linear increase in S(E) at higher energy, and cannot be described by any single values of E 0 and w. Despite the large barrier D 2 dissociation on the ) alloy shows no evidence for vibrational enhancement, in contrast to other activated dissociative chemisorption systems such as H 2 /D 2 on Cu, 13,25 Cu 85 Pd 15 (110)(2 ϫ1), 26 NiAl͑110͒, 16 and Ag͑111͒, 14 as well as dissociation of CH 4 ͑Ref. 33͒ and N 2 ͑Ref.…”

Section: Models For S"e… On (ͱ3؋ͱ3)r30°sn/pt(111)mentioning

confidence: 85%

See 1 more Smart Citation

Deuterium dissociation on ordered Sn/Pt(111) surface alloys

Samson

Nesbitt

Koel

et al. 1998

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

We have explored the effect of alloying an unreactive metal, Sn, on the dynamics of D2 dissociative chemisorption at Pt(111). By comparing D2 sticking and recombinative desorption on Pt(111) with that on the ordered p(2×2) Sn/Pt(111) and (∛×∛)R30° Sn/Pt(111) surface alloys, we examine the influence of the local surface composition on reactivity. The energy dependence of D2 sticking S(E) has been measured for all three surfaces using a hyperthermal beam. We find that the activation barrier for dissociative chemisorption is low on the p(2×2) alloy, but the sticking probability is reduced, compared to Pt(111), by an increase in the steric constraint on the dissociation site. Sticking on the (∛×∛)R30° alloy is inefficient at thermal energies with a threshold of ∼280 meV, below which the sticking probability falls exponentially. The increase in the barrier to D2 dissociation occurs as the stable, high coordination Pt3–D binding sites are lost by formation of the (∛×∛)R30° alloy. Despite the large activation barrier, sticking is dominated by the vibrational ground state with the barrier occurring in the entrance channel, before the D2 bond has stretched. Departures from a normal energy scaling indicate that the dissociation site is localized in the unit cell and we suggest favorable dissociation sites on the alloy surfaces. Estimates for the heats of adsorption, obtained by comparing activation energies to adsorption and desorption, indicate an abrupt decrease in the D binding energy as the Pt3 sites are lost. We show that sticking and desorption parameters are consistent with an increasing steric constraint for adsorption/desorption on the alloy surfaces as the Sn content is increased and an increase in the barrier to dissociation as the stable Pt3 sites are lost by alloying.

show abstract

Section: Dissociation On (ͱ3؋ͱ3)r30°sn/pt(111)mentioning

confidence: 58%

Section: Models For S"e… On (ͱ3؋ͱ3)r30°sn/pt(111)mentioning

confidence: 85%

Deuterium dissociation on ordered Sn/Pt(111) surface alloys

Samson

Nesbitt

Koel

et al. 1998

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…Newton and co-workers 37 have studied the thermal decomposition of formic acid on a Cu 0.85 Pd 0.15 (110) bulk alloy. The structure of the surface that exhibits a (2 × 1) superstructure in LEED has been the focus of considerable attention. ,,− It has been unequivocally demonstrated that the (2 × 1) periodicity has its origin in chemical ordering between Cu and Pd in the second layer in the form of a mixed 50:50 s layer with Pd atoms occupying every second site along the close packed [11̄0] rows. The top layer is Cu-rich. , Newton et al observed a co-incident CO 2 /H 2 TPD peak at 445 K (β = 2.65 K s -1 ) along with a small amount of molecular formic acid desorption.…”

Section: Discussionmentioning

confidence: 99%

“…The structure of the surface that exhibits a (2 × 1) superstructure in LEED has been the focus of considerable attention. 21,37,[42][43][44][45] It has been unequivocally demonstrated that the (2 × 1) periodicity has its origin in chemical ordering between Cu and Pd in the second layer in the form of a mixed 50:50 s layer with Pd atoms occupying every second site along the close packed [11 h0] rows. The top layer is Cu-rich.…”

Section: Discussionmentioning

confidence: 99%

The Growth Mechanism, Thermal Stability, and Reactivity of Palladium Mono- and Multilayers on Cu(110)

Reilly¹,

Barnes²,

Price³

et al. 1999

J. Phys. Chem. B

Self Cite

View full text Add to dashboard Cite

The room-temperature growth of palladium (Pd) on Cu(110) has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and temperature-programmed desorption (TPD). XPS signal versus deposition time plots rule out a simple layer-by-layer growth mechanism. STM/LEED indicates formation of regions of (2 × 1) overlayer at low Pd coverages (θPd < 1 ML), with considerable disorder in the form of monolayer deep pits and islands. Higher Pd coverages lead to the formation of a granular film consisting of densely packed, flat-topped Pd clusters of average size 75 × 150 Å and with largely a rectangular shape. The favored growth mechanism is of multilayered Pd islands above a mixed (2 × 1) CuPd interface of two to three atomic layers thickness. The thermal stability of the Pd/Cu(110) system was investigated with XPS peak intensity versus annealing temperature plots that indicate that bulk intermixing takes place rapidly between 500 and 600 K. The Pd 3d5/2 XPS peak widths narrow, suggesting the formation of a largely homogeneous CuPd surface alloy. STM indicates that heating to 500 K leaves the Pd clusters in a largely unaltered morphology with no sign of Ostwald ripening, whereas annealing to 600 K leads to considerable changes in topography. The granular structure of the Pd film is disrupted, leading to a surface with irregularly shaped flat domains separated by mono-atomic steps. High temperature (720 K) annealing leads to further flattening and appearance of regular parallel lines in STM images. The spacing of these lines varies with Pd loading, and they are assigned to strain due to lattice mismatch between the “capping” copper monolayer and the underlying mixed CuPd alloy. The reactivity of the Pd/Cu(110) surface has been probed by dosing formic acid and monitoring formate decomposition. High Pd coverages lead to a substantial destabilization of the formate relative to clean Cu(110), which is assigned to formate adsorption on mixed CuPd sites.

show abstract

“…In PdCu100, Pd atoms have 1.9% reduced distances with respect to Pd100, PdCu50, or PdCu25 and its Cu atoms show (approximately) an 8% increase in distance with respect to our Cu monometallic reference. A hydride-like lattice expansion effect is completely excluded for samples with Pd:Cu atomic ratios higher than 1 as hydrogen dissociation is a highly activated (Cu-like) process in these systems …”

Section: Discussionmentioning

confidence: 99%

Alloy Formation and Stability in Pd−Cu Bimetallic Catalysts

1996

View full text Add to dashboard Cite

The temperature-programmed reduction of three Pd−Cu/KL-zeolite bimetallic catalysts has been studied using X-ray absorption near edge spectroscopy (XANES) and infrared spectroscopy with the probe molecule CO. We show that complete alloying with electronic perturbation of both components (with respect to their metallic state) is reached over the full range of compositions analyzed. It is also shown that the effect of reduction temperature on the nature of the surfaces exposed by the active phases, as well as the sintering processes, is primarily governed by the Pd:Cu ratio.

show abstract

The influence of electronic structure on D2 activated dissociative chemisorption at Cu85Pd15{110}

Cited by 13 publications

References 53 publications

Deuterium dissociation on ordered Sn/Pt(111) surface alloys

Deuterium dissociation on ordered Sn/Pt(111) surface alloys

The Growth Mechanism, Thermal Stability, and Reactivity of Palladium Mono- and Multilayers on Cu(110)

Alloy Formation and Stability in Pd−Cu Bimetallic Catalysts

Contact Info

Product

Resources

About