Abstrakt
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 approx. 2 nm and single atomic Ce species were presented in mesoporous zeolites after H-2 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.