cs9b01278_si_001.pdf (533.51 kB)
“Intelligent” Pt Catalysts Studied on High-Surface-Area CaTiO3 Films
journal contribution
posted on 2019-07-17, 12:07 authored by Chao Lin, Alexandre C. Foucher, Yichen Ji, Christopher D. Curran, Eric A. Stach, Steven McIntosh, Raymond J. GorteCaTiO3-supported Pt is sometimes referred to as an “Intelligent”
catalyst because Pt can reversibly leave or enter the perovskite lattice
following high-temperature reduction or oxidation; however, slow egress–ingress
kinetics associated with large perovskite crystallites make these
systems impractical. In the present work, thin films (∼1 nm)
of CaTiO3 were deposited onto MgAl2O4 and then examined as catalyst supports for Pt and Pd. While Pd/CaTiO3/MgAl2O4 showed adsorption and CO-oxidation
properties that were essentially the same as Pd/MgAl2O4, the Pt/CaTiO3/MgAl2O4 catalyst
exhibited evidence for strong support interactions. Pt/CaTiO3/MgAl2O4 showed high activity for CO oxidation
following reduction at 1073 K, even though CO adsorption was suppressed,
but the catalysts were dramatically less active after oxidation at
1073 K and reduction at 773 K. Both Pt/CaTiO3/MgAl2O4 and a catalyst formed by ex-solution of CaTi0.95Pt0.05O3 exhibited very low rates
for toluene hydrogenation in comparison to Pt/MgAl2O4. Scanning transmission electron microscopy (STEM) and energy-dispersive
spectroscopy (EDS) showed that the CaTiO3 films uniformly
covered the MgAl2O4 surface after both reduction
and oxidation at 1073 K. Pt particles on reduced Pt/CaTiO3/MgAl2O4 exhibited an unusual rhombohedral
shape and may be flat, a further indication of strong interactions
between the metal and the support. Low-energy ion scattering (LEIS)
indicated that high-temperature reduction caused a restructuring of
the CaTiO3. The implications of these results for understanding
catalysts formed by ex-solution of metals from a perovskite lattice
are discussed.