The
catalytic oxidation of ethane using CO2 as a soft
oxidant could facilitate the utilization of CO2 and ethane
from the shale gas as a raw material to produce value-added ethylene via a dehydrogenation process. Pt and Ce species were supported
on mesoporous zeolite containing surface framework defects, and the
resulting supported catalysts were investigated for the oxidative
dehydrogenation of ethane with CO2. Extended X-ray absorption
fine structure and high-resolution transmission electron microscopy
evidenced that Pt5Ce intermetallic nanoparticles with an
average diameter of ∼2 nm and single atomic Ce species were
presented in mesoporous zeolites after H2 reduction at
973 K. This supported catalyst was highly stable and selective for
ethylene production compared to supported platinum and supported Pt/CeO2@SiO2 catalysts. Characterization of the fresh
and spent catalysts with CO chemisorption, thermogravimetric analyses,
temperature-programmed desorption of ethylene, and electron microscopy
revealed that the supported Pt5Ce intermetallic catalysts
exhibited a much lower affinity for ethylene than monometallic Pt,
which diminishes the possibility of coke formation onto the active
Pt surface due to the over-dehydrogenation reaction of ethylene. Instead,
cokes were predominantly deposited on the zeolite support, which might
be attributed to the olefinic polymerization by weakly acidic silanol
groups at the external surface. In contrast, the monometallic Pt catalyst
exhibited a high affinity for ethylene. The strongly adsorbed ethylene
onto the Pt surface could be further converted into carbonaceous coke,
which caused the rapid deactivation. Furthermore, density functional
theory calculations revealed that single atomic Ce species closed
to Pt5Ce intermetallic nanoparticles elevated the energy
barrier of C–C bond rupture over C–H bond scission,
which significantly suppresses the CO formation via the reforming pathway.
A solvent-free route is developed for preparing nanoscale sodalite zeolite with a multi-hollow structure. Furthermore, the synthesis of nanosized hollow sodalite polycrystalline aggregates with a mesoporous structure and high crystallinity is investigated by adding an organosilane surfactant as a mesopore-generating agent.
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