Forecasting selectivity of Au-based partial oxidation catalysts via temperature programmed desorption studies on the Au(111) model catalyst
Author
Shah, Syed Asad Ali
Advisor
Özensoy, Emrah
Date
2014-09Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Gold-based heterogeneous catalysts have attracted significant attention due to their selective
partial oxidation capabilities which are comparable to that of the industrial homogeneous
benchmark catalysts. In the current study, a planar Au(111) single crystal model catalyst surface
was utilized to understand the behavior of different organic compounds (alcohols, aldehydes,
esters etc.) in conjunction to the partial oxidation reactions. Stability of different organic
compounds were investigated on the Clean Au(III) surface. The stability of a particular organic
compound on the Au(III) model catalyst surface was found to be closely related to the variety of
generated products. Surface sensitive analytical techniques such as Temperature Programmed
Desorption (TPD) and Low Energy Electron Diffraction (LEED) were used to investigate the
interaction of organic compounds with the clean Au(111) single crystal surfaces under ultrahigh
vacuum (UHV) conditions. Organic compounds were dosed onto atomically clean Au(III)
surfaces at the liquid nitrogen temperature. All organic compounds desorbed non-dissociatively
on the clean Au(111) surface. All organic compounds reveal monolayer and multilayer
desorption signals but in the case of aldehydes, desorption is quite different, as they lead to
polymerization on the surface with high desorption temperatures. Zeroth order desorption
kinetics was observed for multilayers, while 1st order desorption was seen for the monolayer. In
most cases, the multilayer feature can be observed with two distinct desorption peaks
associated with amorphous and crystalline phases. In this work, it is confirmed that majority of
the studied compounds have relatively low adsorption energies on Au(111). The species with
lower desorption energies on Au(111) tend to undergo partial oxidation rather than total
oxidation. Thus, desorption energy appears as an important descriptor for predicting the extent
of oxidation in partial/total oxidation in oxidative coupling reactions.
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