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The capture of CO 2 and its reduction with H 2 to form C1 compounds (i.e., CO 2 capture and reduction; CCR), such as CO and CH 4 , using dual-functional materials (DFMs) has recently attracted attention as a promising process for CO 2 emission reduction and utilization. Although CO is more useful than CH 4 from a chemical synthesis perspective, the development of an effective DFM system to generate CO has been explored much less than that for CH 4 generation. This study successfully developed Na-promoted Pt nanoparticles (NPs) supported on Al 2 O 3 (Pt−Na/Al 2 O 3 ) as an effective DFM for selective CO production by capturing diluted CO 2 from a mixture with O 2 and successive reduction by H 2 . The developed Pt−Na/Al 2 O 3 was applicable for continuous CCR operation using two reactors in parallel and switching feed gases. The CO 2 capture ability and productivity of CO were maintained for at least 100 h. We also elucidated the effect of basic promoters through microscopic and spectroscopic characterizations. The Na-modified Pt nanoparticles (NPs) were formed on Al 2 O 3 , where Na species play two important roles in efficient CO 2 capture and selective CO formation: (i) capturing CO 2 from a mixture with O 2 and (ii) inhibiting the adsorption of generated CO on Pt NPs.

Kinetic analyses of Ce 4+ ↔ Ce 3+ redox and CO 2 /H 2 formation for the unsteady-state water−gas shift (WGS) reaction under periodic CO ↔ H 2 O feeds to Cu/CeO 2 catalysts are carried out by in situ/operando ultraviolet−vis and infrared studies at 350 °C. Under CO, the Ce 4+ −OH species are reduced to produce H 2 , CO 2 , and Ce 3+ −□ (oxygen vacancy). Under the subsequent feed of H 2 O, Ce 3+ −□ is reoxidized by H 2 O to yield H 2 and Ce 4+ −OH species. The rates of Ce 4+ reduction/ Ce 3+ reoxidation are close to those of CO 2 /H 2 formation for various Cu/CeO 2 catalysts with different Cu loadings, providing quantitative evidence of the redoxbased mechanism of the unsteady-state WGS reaction. Ce 3+ −□ reoxidation by H 2 O has a lower apparent barrier than the Ce 4+ −O reduction step. The H 2 O-promoted desorption of the adsorbed carbonates is responsible for CO 2 formation under H 2 O.The characterization results suggest that the number of interfacial sites between the CeO 2 and Cu species increases with decreasing Cu loading. Turnover frequencies per surface Cu site for the Ce 4+ ↔ Ce 3+ redox reaction and CO 2 /H 2 formation increase with the number of interface sites. An associative redox mechanism based on the redox reaction between the oxidized state (Cu 2+ −OH adjacent to Ce 4+ and Ce 4+ −OH) and the reduced state (Cu + −□−Ce 3+ ) is proposed as the main catalytic cycle of the unsteady-state WGS reaction.

In this study, operando Ce K-edge XANES measurements of CeO2-supported Ni (Ni/CeO2) catalysts for chemical looping dry reforming of methane (CLDRM) were performed. Low-loading Ni/CeO2 was effective for selectively promoting the partial oxidation of CH4 and suppressing coke deposition. Operando XANES measurements confirmed the redox state of Ce oxide in CLDRM and revealed that the reoxidation of reduced Ce oxide during CO2 reduction was faster than the reduction of Ce oxide during CH4 oxidation.

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