Understanding Activation of Small Molecules with Light:
Photothermal Vs. Charge Carrier Effects in Photocatalysis
Jennifer Strunk
Technical University of Munich
When photocatalysts are irradiated with high intensity light
sources, it is expected that
the samples will also heat up, at
least locally. Then, in addition to direct light-driven
reactions with excited charge carriers, more conventional thermal
reactions are also
possible, similar to classical catalysis.
This is especially the case when nanoparticles
of the coinage
metals Cu, Ag and Au are involved, which show intense plasmon
absorption bands.
Here, two photocatalyst systems are
presented in which we were able to clearly identify
photothermal effects as main reason for improved (photo)catalytic
performance. For
the case of Au/TiO2, Anti-Stokes Raman
spectroscopy was used to track temperature
changes in the
anatase phase of TiO2, when the plasmon excitation of gold was
triggered with a green laser. Under these conditions, the titania
reached temperatures
significantly exceeding 1000 K, which over
time caused severe rutilization of titania.
Even under
irradiation with common UV-Vis research light sources, rutilization of
titania
was identified in Au/TiO2, so local temperatures above
the rutilization threshold
(~850 K) can be reached in this
case, too. At these temperatures, many catalytic
reactions of
relevance reach thermodynamic equilibrium, so it is expected that
thermal
effects are dominant for Au/TiO2, with little or no
influence of photogenerated charge
carriers in either Au or
TiO2.
In the second case, Cu/ZnO-based catalysts were
considered for light-assisted
thermocatalytic CO2 valorization
near ambient pressure. Both methanol synthesis and
CO formation
by the reverse water gas shift were detected to be influenced by
light
irradiation. The endothermic reverse water gas shift was
always favored over
exothermic methanol synthesis, regardless
of whether UV or visible light or both was
used. The behavior
of forward and reverse reaction rate, together with detailed in situ
characterization of the material and the reaction mechanism,
suggested that the light
simply caused the active sites,
predominantly the copper, to be locally at much higher
temperature. The larger influence of visible light suggests a
dominant influence of the
Cu plasmon absorption rather than
band-gap excitation in ZnO.
Understanding Activation of Small Molecules
with Light:
\nPhotothermal Vs. Charge Carrier Effects in
Photocatalysis
\nJennifer Strunk
\nTechnical University of
Munich
\nWhen photocatalysts are irradiated with high intensity
light sources, it is expected that
\nthe samples will also heat up,
at least locally. Then, in addition to direct light-driven
\nreactions with excited charge carriers, more conventional thermal
reactions are also
\npossible, similar to classical catalysis. This
is especially the case when nanoparticles
\nof the coinage metals
Cu, Ag and Au are involved, which show intense plasmon
\nabsorption
bands.
\nHere, two photocatalyst systems are presented in which we
were able to clearly identify
\nphotothermal effects as main reason
for improved (photo)catalytic performance. For
\nthe case of
Au/TiO2, Anti-Stokes Raman spectroscopy was used to track temperature
\nchanges in the anatase phase of TiO2, when the plasmon excitation of
gold was
\ntriggered with a green laser. Under these conditions,
the titania reached temperatures
\nsignificantly exceeding 1000 K,
which over time caused severe rutilization of titania.
\nEven under
irradiation with common UV-Vis research light sources, rutilization of
titania
\nwas identified in Au/TiO2, so local temperatures above
the rutilization threshold
\n(~850 K) can be reached in this case,
too. At these temperatures, many catalytic
\nreactions of relevance
reach thermodynamic equilibrium, so it is expected that thermal
\neffects are dominant for Au/TiO2, with little or no influence of
photogenerated charge
\ncarriers in either Au or TiO2.
\nIn
the second case, Cu/ZnO-based catalysts were considered for
light-assisted
\nthermocatalytic CO2 valorization near ambient
pressure. Both methanol synthesis and
\nCO formation by the reverse
water gas shift were detected to be influenced by light
\nirradiation. The endothermic reverse water gas shift was always
favored over
\nexothermic methanol synthesis, regardless of whether
UV or visible light or both was
\nused. The behavior of forward and
reverse reaction rate, together with detailed in situ
\ncharacterization of the material and the reaction mechanism,
suggested that the light
\nsimply caused the active sites,
predominantly the copper, to be locally at much higher
\ntemperature. The larger influence of visible light suggests a
dominant influence of the
\nCu plasmon absorption rather than
band-gap excitation in ZnO.
Abstract:
Aviation contributes 2-3% of global CO2 emissions. Sustainable Aviation Fuels (SAF) is one of the viable options for reduction of these emissions. The heterogeneously catalyzed co-oligomerization of lower olefins produced from methanol to SAF is already successfully demonstrated. In this study, the mixture of lower olefins like ethylene, propylene and 1-butylene are employed as a feedstock and are heterogeneously co-oligomerized over nickel on Amorphous Silica Alumina (ASA) support. The deactivation of catalyst is noticed after 10 h. Extensive investigations are carried out on spent catalyst to understand the mechanism for deactivation. The nickel catalyst tends to sinter, migrate to the support, leach and coke rapidly resulting in the deactivation even at low process temperatures employed like 200 °C.
Abstract:
\n\nAviation contributes 2-3% of global CO2 emissions. Sustainable Aviation Fuels (SAF) is one of the viable options for reduction of these emissions. The heterogeneously catalyzed co-oligomerization of lower olefins produced from methanol to SAF is already successfully demonstrated. In this study, the mixture of lower olefins like ethylene, propylene and 1-butylene are employed as a feedstock and are heterogeneously co-oligomerized over nickel on Amorphous Silica Alumina (ASA) support. The deactivation of catalyst is noticed after 10 h. Extensive investigations are carried out on spent catalyst to understand the mechanism for deactivation. The nickel catalyst tends to sinter, migrate to the support, leach and coke rapidly resulting in the deactivation even at low process temperatures employed like 200 °C.
\n DTSTART;TZID=Europe/Berlin:20260504T130000 DTEND;TZID=Europe/Berlin:20260504T133000 LOCATION:IKFT Seminar Room 202, Building 727 END:VEVENT BEGIN:VEVENT UID: 61209 DTSTAMP:20260409T202956Z SUMMARY:Development of a two-step continuous process for reductive catalytic fractionation of lignocellulosic biomass into aromatic compounds. X-ALT-DESC;FMTTYPE=text/html:Abstract:
A two-step RCF process is used. In the first step, lignin is dissolved by solvation in a flow reactor as well as in batch mode, thereby separating lignin from carbohydrates. In the second step, the lignin solution obtained in the first step is catalytically reduced in a batch reactor to gain data for the design of a continuous fixed-bed reactor. In the second step, the formic acid produced by the decomposition of hemicellulose and solvent is used as the hydrogen source.
Abstract:
\n\nA two-step RCF process is used. In the first step, lignin is dissolved by solvation in a flow reactor as well as in batch mode, thereby separating lignin from carbohydrates. In the second step, the lignin solution obtained in the first step is catalytically reduced in a batch reactor to gain data for the design of a continuous fixed-bed reactor. In the second step, the formic acid produced by the decomposition of hemicellulose and solvent is used as the hydrogen source.
\n\n\n DTSTART;TZID=Europe/Berlin:20260721T130000 DTEND;TZID=Europe/Berlin:20260721T133000 LOCATION:IKFT Seminar Room 202, Building 727 END:VEVENT BEGIN:VEVENT UID: 61210 DTSTAMP:20260409T202956Z SUMMARY:Techno-economic assessment of by-products from carbon capture and utilization processes X-ALT-DESC;FMTTYPE=text/html: