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Title: Ethylene hydrogenation on Pt(111) monitored in situ at high pressures using sum frequency generation

Abstract

Infrared-visible sum frequency generation (SFG) has been used to monitor the surface vibrational spectrum in situ during ethylene hydrogenation on Pt(111). Measurements were made near 1 atm of total pressure of ethylene and hydrogen and at 395 K. Kinetic information was obtained simultaneously with the surface vibrational spectroscopy by monitoring the reaction rate with gas chromatography. The macroscopic turnover rate and surface adsorbate concentration could then be correlated. During the reaction ethylidyne, di-{sigma}-bonded ethylene, ethyl, and {pi}-bonded ethylene were observed on the surface in various amounts depending on conditions. Ethylidyne, a spectator species during hydrogenation, competed directly for sites with di-{sigma}-bonded ethylene and its surface concentration could be shown to be completely uncorrelated with the rate of hydrogenation. In contrast, {pi}-bonded ethylene did not compete for sites with the ethylidyne overlayer and was observed on the surface regardless of the surface concentration of ethylidyne. Evidence points to the {pi}-bonded species as being the primary intermediate in ethylene hydrogenation on Pt(111). The surface concentration of this species is about 0.04 ML (ML = monolayer) during reaction. Thus, the turnover rate per reaction intermediate is 25 times faster than the turnover rate if measured per surface platinum atom. 30 refs., 11 figs.

Authors:
; ; ;  [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
226672
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 118; Journal Issue: 12; Other Information: PBD: 27 Mar 1996
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 36 MATERIALS SCIENCE; ETHYLENE; HYDROGENATION; ENERGY SPECTRA; REACTION INTERMEDIATES; ABUNDANCE; PLATINUM; VIBRATIONAL STATES; CHEMICAL REACTION KINETICS; PRESSURE DEPENDENCE

Citation Formats

Cremer, P S, Su, X, Shen, Y R, Somorjai, G A, and Lawrence Berkeley Lab., CA. Ethylene hydrogenation on Pt(111) monitored in situ at high pressures using sum frequency generation. United States: N. p., 1996. Web. doi:10.1021/ja952800t.
Cremer, P S, Su, X, Shen, Y R, Somorjai, G A, & Lawrence Berkeley Lab., CA. Ethylene hydrogenation on Pt(111) monitored in situ at high pressures using sum frequency generation. United States. doi:10.1021/ja952800t.
Cremer, P S, Su, X, Shen, Y R, Somorjai, G A, and Lawrence Berkeley Lab., CA. Wed . "Ethylene hydrogenation on Pt(111) monitored in situ at high pressures using sum frequency generation". United States. doi:10.1021/ja952800t.
@article{osti_226672,
title = {Ethylene hydrogenation on Pt(111) monitored in situ at high pressures using sum frequency generation},
author = {Cremer, P S and Su, X and Shen, Y R and Somorjai, G A and Lawrence Berkeley Lab., CA},
abstractNote = {Infrared-visible sum frequency generation (SFG) has been used to monitor the surface vibrational spectrum in situ during ethylene hydrogenation on Pt(111). Measurements were made near 1 atm of total pressure of ethylene and hydrogen and at 395 K. Kinetic information was obtained simultaneously with the surface vibrational spectroscopy by monitoring the reaction rate with gas chromatography. The macroscopic turnover rate and surface adsorbate concentration could then be correlated. During the reaction ethylidyne, di-{sigma}-bonded ethylene, ethyl, and {pi}-bonded ethylene were observed on the surface in various amounts depending on conditions. Ethylidyne, a spectator species during hydrogenation, competed directly for sites with di-{sigma}-bonded ethylene and its surface concentration could be shown to be completely uncorrelated with the rate of hydrogenation. In contrast, {pi}-bonded ethylene did not compete for sites with the ethylidyne overlayer and was observed on the surface regardless of the surface concentration of ethylidyne. Evidence points to the {pi}-bonded species as being the primary intermediate in ethylene hydrogenation on Pt(111). The surface concentration of this species is about 0.04 ML (ML = monolayer) during reaction. Thus, the turnover rate per reaction intermediate is 25 times faster than the turnover rate if measured per surface platinum atom. 30 refs., 11 figs.},
doi = {10.1021/ja952800t},
journal = {Journal of the American Chemical Society},
number = 12,
volume = 118,
place = {United States},
year = {1996},
month = {3}
}