Molecular Diffusion, Adsorption, and Reaction on High Area Oxide Surfaces as Studied by FT-IR

by Kim, Sunhee

Abstract (Summary)
Molecular diffusion, adsorption, and reaction on high surface area Al2O3 were studied by using transmission infrared spectroscopy and temperature programmed desorption techniques. It was demonstrated that triethylenediamine (TEDA) binds to Al-OH Br©ªnsted acid sites via hydrogen bonding as well as to Al3+ Lewis acid sites on a partially dehydroxylated ¥ã-Al2O3 powder at 300 K. The adsorption of a series of CWAs (Chemical Warfare Agents) such as carbon monoxide, hydrogen cyanide, and cyanogen chloride on the TEDA-functionalized Al2O3 surface was studied to determine the role of TEDA on the enhancement of the adsorption properties of ¥ã-Al2O3 adsorbent by a combination of FTIR and density functional theory studies. No direct binding of the gases to the exposed amine group of a TEDA molecule pre-adsorbed on ¥ã-Al2O3 is found. Instead the TEDA molecule effectively competes with the gases for binding sites on the ¥ã-Al2O3 surface and only site blocking effects by TEDA are observed. A new method was developed to study the diffusion properties of molecules into compressed powdered samples using transmission IR spectroscopy. The diffusion of 2-CEES (2-chloroethylethyl sulfide) molecules from a condensed film which formed at lower temperature into the interior of two different particle size Al2O3 powders was monitored and compared by using the isolated Al-OH species as spectroscopic sensors of the arrival of diffusing 2-CEES molecules. The diffusion of the 2-CEES molecule into the subnano-Al2O3 powder particles is more rapid than in the multinano-Al2O3 particles. A surface diffusion mechanism was used to model the diffusion process giving good agreement with the experimental results. The infrared spectroscopic technique for surface diffusion studies was applied to monitor the transport of CO to the Pt cores of Pt@CoO yolk-shell nanoparticles by probing the development of characteristic IR modes of the adsorbed CO species on the Pt yolk. It was found that the transport of CO occurs by an activated surface diffusion process through the ~ 5 nm thick shell of CoO, surrounding ~ 2 nm diameter Pt cores. In addition the infrared spectrum of the CO molecule diffusing through the CoO shells is detected by high sensitivity measurements.
Bibliographical Information:

Advisor:Sunil Saxena; John T. Yates, Jr.; David H. Waldeck; J. Karl Johnson

School:University of Pittsburgh

School Location:USA - Pennsylvania

Source Type:Master's Thesis



Date of Publication:09/20/2007

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