posted on 2024-02-16, 06:44authored byMykhailo Vaidulych, Li-Ya Yeh, Robin Hoehner, Juraj Jašík, Shashikant A. Kadam, Michael Vorochta, Ivan Khalakhan, Jan Hagen, Štefan Vajda
Films of titania-supported
monometallic Pd, Pt, and bimetallic
Pt–Pd catalysts made of metallic nanoparticles were prepared
by magnetron sputtering and studied in the oxidative dehydrogenation
(ODH) of cyclohexene. Pd/TiOx and Pt–Pd/TiOx were found active at as low temperature
as 150 °C and showed high catalytic activity with high conversion
(up to 81%) and benzene selectivity exceeding 97% above 200 °C.
In turn, the Pt/TiOx catalyst performed
poorly with the onset of benzene production at 200 °C only and
conversions not exceeding 5%. The activity of bimetallic Pt–Pd
catalysts far exceeded all of the other investigated catalysts at
temperatures below 250 °C. However, the production of benzene
significantly dropped with a further temperature increase due to the
enhanced combustion of CO2 at the expense of benzene formation.
As in situ NAP-XPS measurement of the Pt–Pd/TiOx catalyst in the reaction conditions of the ODH of
cyclohexene revealed Pd surface enrichment during the first temperature
ramp, we assume that Pd surface enrichment is responsible for enhanced
activity at low temperatures in the bimetallic catalyst. At the same
time, the Pt constituent contributes to stronger cyclohexene adsorption
and oxygen activation at elevated temperatures, leading to changes
in conversion and selectivity with a drop in benzene formation and
increased combustion to CO2. Both the monometallic Pd and
the Pt–Pd-based catalysts produced a small amount of the second
valuable product, cyclohexadiene, and below 250 °C produced only
a negligible amount of CO2 (<0.2%). To summarize, Pd-
and Pt–Pd-based catalysts were found to be promising candidates
for highly selective low-temperature dehydrogenation of cyclic hydrocarbons
that showcased reproducibility and stability after the temperature
activation. Importantly, these catalysts were fabricated by utilizing
proven methods suitable for large-scale production on extended surfaces.