G.M. Haselmann, B. Baumgartner, J. Wang, K. Wieland, T. Gupta, C. Herzig, A. Limbeck, B. Lendl, D. Eder:
"In Situ Pt Photodeposition and Methanol Photooxidation on Pt/TiO2: Pt-Loading-Dependent Photocatalytic Reaction Pathways Studied by Liquid-Phase Infrared Spectroscopy";
ACS Catalysis, 10 (2020), 5; S. 2964 - 2977.

Kurzfassung englisch:
We developed a top-irradiated, liquid-phase attenuated
total reflectance Fourier transform infrared (ATR-FTIR) setup
that allows time-resolved investigations of both Pt particle growth
during in situ photodeposition via monitoring of the Pt0−COads
band on TiO2 thin films as well as the photooxidation of methanol in
aqueous environments. Obtained ATR-FTIR data sets were analyzed
via multivariate curve resolution-alternating least squares (MCRALS),
which enabled us to clearly differentiate various reaction
pathways for different Pt loadings at otherwise fixed reaction
conditions (i.e., methanol concentration, UV intensity). At the
highest Pt loading (nominal concentration of 2.7 wt %), photooxidation
of methanol occurs via direct oxidation through a formaldehyde intermediate to CO2, whereas the lower Pt loadings of 0.7
and 1.4 wt % favor a side reaction that includes methyl formate as an intermediate. These findings were correlated with the
formation of different CO binding sites on Pt during photodeposition, and we presume that changes in the reaction pathway depend
on the number rather than the nature of active available Pt sites. Complementary ex situ characterizations of the thin films by
transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),
and inductively coupled plasma mass spectrometry (ICP-MS) were performed, delivering information on the generated Pt
nanoparticles and structural changes of TiO2. The presented optical setup paves the way for fundamental studies of heterogeneous
catalytic reactions as close as possible to their actual use in aqueous systems.

In situ infrared spectroscopy, photocatalysis, reaction monitoring, TiO2, carbon monoxide, methyl formate, photodeposition

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