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Title: Isothermal kinetic measurements for the hydrogenation of ethylene on Pt(111) under vacuum: Significance of weakly-bound species in the reaction mechanism

Abstract

The kinetics of the hydrogenation of ethylene on Pt(111) was studied isothermally and under vacuum by using a variation of the dynamic molecular beam method originally devised by King and Wells. At surface temperatures above 240 K ethylidyne formation competes with both ethylene hydrogenation and ethylene desorption. At temperatures below 240 K, on the other hand, the decomposition of ethylene is slow, and the adsorption and hydrogenation kinetics for ethylene on both clean and hydrogen-covered surfaces could be investigated independently. Ethylene adsorption was found to be precursor-mediated at low coverages and Langmuirian near saturation. A certain population of weakly-adsorbed species can also be maintained at coverages near saturation by exposure of the surface to a constant flux of ethylene molecules. The presence of coadsorbed hydrogen reduces the total ethylene uptake but increases the amount of weakly-adsorbed ethylene as compared to that on the clean Pt(111). The main conclusion from this work is the fact that this weakly-adsorbed species appears to be essential for the hydrogenation of ethylene: the kinetic orders of the reaction were determined to be 1.2{+-}0.3 and 0.8{+-}0.2 with respect to the weakly-adsorbed ethylene and hydrogen surface coverages, respectively. An activation energy of 6{+-}1 kcal/mol was measured formore » the hydrogenation of ethylene to ethane under the conditions of these experiments. 50 refs., 18 figs.« less

Authors:
;  [1]
  1. Univ. of California, Riverside, CA (United States)
Publication Date:
OSTI Identifier:
501887
DOE Contract Number:  
FG03-94ER14472
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 101; Journal Issue: 3; Other Information: PBD: 16 Jan 1997
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 36 MATERIALS SCIENCE; ETHYLENE; CHEMICAL REACTION KINETICS; DECOMPOSITION; CATALYSIS; ADSORPTION; HYDROGENATION; PRESSURE DEPENDENCE; ACTIVATION ENERGY; PLATINUM

Citation Formats

Oefner, H, and Zaera, F. Isothermal kinetic measurements for the hydrogenation of ethylene on Pt(111) under vacuum: Significance of weakly-bound species in the reaction mechanism. United States: N. p., 1997. Web. doi:10.1021/jp963030q.
Oefner, H, & Zaera, F. Isothermal kinetic measurements for the hydrogenation of ethylene on Pt(111) under vacuum: Significance of weakly-bound species in the reaction mechanism. United States. https://doi.org/10.1021/jp963030q
Oefner, H, and Zaera, F. 1997. "Isothermal kinetic measurements for the hydrogenation of ethylene on Pt(111) under vacuum: Significance of weakly-bound species in the reaction mechanism". United States. https://doi.org/10.1021/jp963030q.
@article{osti_501887,
title = {Isothermal kinetic measurements for the hydrogenation of ethylene on Pt(111) under vacuum: Significance of weakly-bound species in the reaction mechanism},
author = {Oefner, H and Zaera, F},
abstractNote = {The kinetics of the hydrogenation of ethylene on Pt(111) was studied isothermally and under vacuum by using a variation of the dynamic molecular beam method originally devised by King and Wells. At surface temperatures above 240 K ethylidyne formation competes with both ethylene hydrogenation and ethylene desorption. At temperatures below 240 K, on the other hand, the decomposition of ethylene is slow, and the adsorption and hydrogenation kinetics for ethylene on both clean and hydrogen-covered surfaces could be investigated independently. Ethylene adsorption was found to be precursor-mediated at low coverages and Langmuirian near saturation. A certain population of weakly-adsorbed species can also be maintained at coverages near saturation by exposure of the surface to a constant flux of ethylene molecules. The presence of coadsorbed hydrogen reduces the total ethylene uptake but increases the amount of weakly-adsorbed ethylene as compared to that on the clean Pt(111). The main conclusion from this work is the fact that this weakly-adsorbed species appears to be essential for the hydrogenation of ethylene: the kinetic orders of the reaction were determined to be 1.2{+-}0.3 and 0.8{+-}0.2 with respect to the weakly-adsorbed ethylene and hydrogen surface coverages, respectively. An activation energy of 6{+-}1 kcal/mol was measured for the hydrogenation of ethylene to ethane under the conditions of these experiments. 50 refs., 18 figs.},
doi = {10.1021/jp963030q},
url = {https://www.osti.gov/biblio/501887}, journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = 3,
volume = 101,
place = {United States},
year = {1997},
month = {1}
}