posted on 2020-03-16, 21:43authored byConstantin
A. Walenta, Carla Courtois, Sebastian L. Kollmannsberger, Moritz Eder, Martin Tschurl, Ueli Heiz
Photocatalytic hydrogen evolution from methanol is a standard test
reaction for photocatalyst materials. Surprisingly, the exact chemical
mechanism is still widely discussed in the literature. In order to
disentangle photochemical from thermal reaction steps and gain insights
on the atomic level, we use a Pt cluster-loaded TiO2(110)
photocatalyst in very well-defined environments. Using Auger electron
spectroscopy, temperature-programmed desorption/reaction, isotopic
labeling, and isothermal photoreactions, it is possible to identify
the surface species present on the catalyst under photocatalytic conditions.
Furthermore, an initial conditioning of the photocatalyst is observed
and attributed to thermal dehydrogenation of methanol to CO species
on the cluster. The analysis of the isothermal photoreactions reveals
that the photo-oxidation kinetics are not significantly affected by
cocatalyst loading. The observed conversion and product distribution
of formaldehyde and methyl formate can be rationalized with kinetic
parameters gained from the bare TiO2(110) crystal. The
work leads to a detailed mechanistic understanding of the surface
species and paves the way for an educated microkinetic modeling approach,
which may be extended to a variety of noble metal cocatalysts and
other TiO2 modifications.