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Direct and indirest channels to molecular dissociation at metal surfaces

Direct and indirest channels to molecular dissociation at metal surfaces
Direct and indirest channels to molecular dissociation at metal surfaces

The influence of well-defined (100) steps on the dynamics of the dissociative chemisorption of methane, hydrogen and ammonia on Pt(533) has been investigated using molecular beam techniques and TPD spectroscopy.

For CH4 on Pt(533), the enhancement in dissociation is associated with the additional direct sticking mediated by the step sites which exhibit an effective activation barrier 300meV lower than the (111) terraces. The lowest activation barrier appears for incident trajectories with an angle of ~5 - 10o compared to the surface normal. An enhanced surface temperature dependence is also observed on the Pt(533) surface over Pt(111), resulting either from the lower barrier to dissociation or the lower effective Debye temperature of the Pt atoms, as the step.

H2 adsorption on Pt(533) exhibits 3 channels to dissociation, a direct channel which is the main one above 30meV, and two indirect channels. One accommodated channel which influence the sticking below 25meV and one unaccommodated channel which has a decreasing influence up to 150meV where S0(H2) stays constant at ~0.05. The unaccommodated indirect channel is not available on CO and O steps-decorated surface. The production of water from hydrogen adsorption on the O/Pt(533) is limited by the formation of hydroxyl.

Ammonia adsorption is molecular at Ts < 400 K and does not seem to depend strongly on the platinum surface plane, however desorption from the (100) steps of Pt(533) appears as extra shoulders on the TPD spectra. Ammonia decomposes on Pt(533) at Ts > 360 K but does not on Pt(111). The dissociation of NH3 occurs in two steps: NH2 is formed and H2 produced at 400 K, then N2 and H2 both desorb at 530K.

University of Southampton
Mormiche, Claire
2c0fe833-de6d-4688-9b9e-4777869b4252
Mormiche, Claire
2c0fe833-de6d-4688-9b9e-4777869b4252

Mormiche, Claire (2002) Direct and indirest channels to molecular dissociation at metal surfaces. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The influence of well-defined (100) steps on the dynamics of the dissociative chemisorption of methane, hydrogen and ammonia on Pt(533) has been investigated using molecular beam techniques and TPD spectroscopy.

For CH4 on Pt(533), the enhancement in dissociation is associated with the additional direct sticking mediated by the step sites which exhibit an effective activation barrier 300meV lower than the (111) terraces. The lowest activation barrier appears for incident trajectories with an angle of ~5 - 10o compared to the surface normal. An enhanced surface temperature dependence is also observed on the Pt(533) surface over Pt(111), resulting either from the lower barrier to dissociation or the lower effective Debye temperature of the Pt atoms, as the step.

H2 adsorption on Pt(533) exhibits 3 channels to dissociation, a direct channel which is the main one above 30meV, and two indirect channels. One accommodated channel which influence the sticking below 25meV and one unaccommodated channel which has a decreasing influence up to 150meV where S0(H2) stays constant at ~0.05. The unaccommodated indirect channel is not available on CO and O steps-decorated surface. The production of water from hydrogen adsorption on the O/Pt(533) is limited by the formation of hydroxyl.

Ammonia adsorption is molecular at Ts < 400 K and does not seem to depend strongly on the platinum surface plane, however desorption from the (100) steps of Pt(533) appears as extra shoulders on the TPD spectra. Ammonia decomposes on Pt(533) at Ts > 360 K but does not on Pt(111). The dissociation of NH3 occurs in two steps: NH2 is formed and H2 produced at 400 K, then N2 and H2 both desorb at 530K.

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Published date: 2002

Identifiers

Local EPrints ID: 464809
URI: http://eprints.soton.ac.uk/id/eprint/464809
PURE UUID: b6574f18-966c-450e-b376-3dfc04612c31

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Date deposited: 05 Jul 2022 00:02
Last modified: 05 Jul 2022 03:13

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Contributors

Author: Claire Mormiche

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