Chenxi Dong,Xupeng Zong,Ziwen Liu,Lijuan Niu,Zhao Zhao,Li An,Dan Qu,Xiayan Wang,Zaicheng Sun
Molecular oxygen (O 2 ) activation is a critical step in the low-temperature catalytic oxidation of carbon monoxide (CO). Photocatalysis is a facile way to activate O 2 to superoxide radicals under mild conditions. Photothermal catalysis, which integrates the photocatalysis of semiconductors and the thermocatalysis of noble metals, has arisen as an appealing strategy to achieve low-temperature catalytic oxidation. Here, we report that Pd/PdO/CeO 2 shows that the temperature of 90% CO conversion dropped by 30°C–50°C under irradiation. The apparent activation energy reduces from 64.6 kJ ⋅ mol −1 to 44.6 kJ ⋅ mol −1 . Pd/PdO/TiO 2 and Pd/PdO/Al 2 O 3 are prepared and compared to understand the underlying mechanism. The results reveal that photocatalysis is vital in lowering the apparent activation energy besides the photothermal effect. The photo-generated electrons promote O 2 activation to generate the superoxide anion. The hole can activate the adsorbed CO on the PdO. These active species are beneficial for lowering the CO oxidation temperature.
Electrochemically driven carbon dioxide (CO 2 ) conversion is an emerging research field due to the global warming and energy crisis. Carbon monoxide (CO) is one key product during electroreduction of CO 2 ; however, this reduction process suffers from tardy kinetics due to low local concentration of CO 2 on a catalyst's surface and low density of active sites. Herein, presented is a combination of experimental and theoretical validation of a Ni porphyrin-based covalent triazine framework (NiPor-CTF) with atomically dispersed NiN 4 centers as an efficient electrocatalyst for CO 2 reduction reaction (CO 2 RR). The high density and atomically distributed NiN 4 centers are confirmed by aberration-corrected high-angle annular dark field scanning transmission electron microscopy and extended X-ray absorption fine structure. As a result, NiPor-CTF exhibits high selectivity toward CO 2 RR with a Faradaic efficiency of >90% over the range from −0.6 to −0.9 V for CO conversion and achieves a maximum Faradaic efficiency of 97% at −0.9 V with a high current density of 52.9 mA cm −2 , as well as good long-term stability. Further calculation by the density functional theory method reveals that the kinetic energy barriers decreasing for *CO 2 transition to *COOH on NiN 4 active sites boosts the performance.
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