2 research outputs found
Identifying the Thermal Decomposition Mechanism of Guaiacol on Pt 111 An Integrated X ray Photoelectron Spectroscopy and Density Functional Theory Study
Using
a concerted effort from both experiment and theory, we determine
the thermal decomposition mechanism for guaiacol on Pt(111), a reaction
of interest in the area of bio-oil upgrading. This work serves as
a demonstration of the power of combining in situ temperature-programmed
X-ray photoelectron spectroscopy (TPXPS) and density functional theory
(DFT) to elucidate complex reaction mechanisms occurring on heterogeneous
surfaces. At low temperature (230 K), guaiacol was found to chemisorb
with the aromatic ring parallel to the Pt(111) surface with five distinct
carbon species and three oxygen species. As the temperature was increased,
TPXPS showed several significant changes to the surface species. The
increase in the species associated with the decomposition of the functional
groups of guaiacol is followed by their subsequent disappearance and
an increase in the nonaromatic carbon signal. On the basis of an energetic
analysis of the various mechanisms using DFT, along with the comparison
of the experimentally and theoretically derived core-level binding
energies, we determined that guaiacol’s decomposition mechanism
occurs via the dehydrogenation of both the methyl and hydroxyl functional
groups, followed by demethylation of the CH<sub>2</sub> or CH group
to form 1,2-benzoquinone. Further heating to above 375 K likely breaks
the aromatic ring and results in the rapid formation and desorption
of CO, accounting for the disappearance of the O 1s signal above 450
K. These results show that a knowledgeable application of TPXPS and
DFT can result in the quantitative identification of surface species
during complex reactions, providing insight useful for the design
of future heterogeneous surfaces