Direct design of low temperature oxidative coupling of methane (OCM) catalysts is proposed via machine learning and data mining. 58 OCM catalysts are experimentally synthesized and evaluated. Collected 58 data...
This
study investigated the thermal decomposition behaviors of
platinum oxide (PtO2) nanoparticles deposited on polycrystalline
TiO2 in different crystal phases. The dissociation of PtO2 to metallic platinum in air occurred at 400 °C on anatase
TiO2 (Pt/TiO2-A), but required 650 °C or
higher on rutile TiO2 (Pt/TiO2-R). The higher
thermal stability of PtO2 on rutile TiO2 is
caused by thermodynamic effect and rather than kinetic effect. In
contrast to the thermodynamic prediction, metallic Pt (Pt0) on TiO2-R was reversibly oxidized to PtO2 (Pt4+) at 650 °C. This behavior was attributed to
the coherent interface structure formed by strong interactions between
PtO2 and rutile TiO2, as revealed by combined
extended X-ray adsorption spectroscopy (EXAFS) and density functional
theory (DFT) studies. At the optimized interface structure, between
the (100) planes of α-PtO2 and rutile TiO2, the interface formation energy was −17.04 kJ mol–1 Å–2 versus −9.84 kJ mol–1 Å–2 in the anatase TiO2 model.
The larger interface formation energy provides a stabilizing effect
against PtO2 dissociation. Therefore, the widely used Pt-loaded
rutile TiO2 typifies the interfacial interactions under
an oxidizing atmosphere, which differ from the strong metal–support
interactions prevailing under a reducing atmosphere.
Platinum
supported on Ta2O5 was found to be a very active
and stable catalyst for SO3 decomposition, which is a key
reaction in solar thermochemical water splitting processes. During
continuous reaction testing at 600 °C for 1,800 h, the Pt/Ta2O5 catalyst showed no noticeable deactivation (activity
loss ≤ 1.5% per 1,000 h). This observed stability is superior
to that of the Pt catalyst supported on anatase TiO2 developed
in our previous study and to those of Pt catalysts supported on other
SO3-resistant metal oxides Nb2O5 and
WO3. The higher stability of Pt/Ta2O5 is due to the abundance of metallic Pt (Pt0), which favors
the dissociative adsorption of SO3 and the smooth desorption
of the products (SO2 and O2). This feature is
in accordance with a lower activation energy and a less negative partial
order with respect to O2. Pt sintering under the harsh
reaction environment was also suppressed to a significant extent compared
to that observed with the use of other support materials. Although
a small fraction of the Pt particles were observed to have grown to
more than several tens of nanometers in size, nanoparticles smaller
than 5 nm were largely preserved and were found to play a key role
in stable SO3 decomposition.
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