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106. CO2Hydrogenation to Methanol over a Pt-Loaded Molybdenum Suboxide Nanosheet with Abundant Surface Oxygen Vacancies

Author

Kuwahara, Yasutaka, Jinda, Akiya, Ge, Hao, Hamahara, Koji, and Yamashita, Hiromi

Abstract

Hydrogenation of carbon dioxide (CO2) using CO2-free hydrogen (H2) to produce methanol (CH3OH) is a promising reaction that can alleviate both carbon emissions and the dependence on fossil fuels. Nonstoichiometric molybdenum suboxide coupled with Pt nanoparticles (NPs) acts as a promising catalyst for this reaction, in which surface oxygen vacancies (VO) and the redox ability of Mo in molybdenum suboxide are the keys to transforming CO2into the CO intermediate and further to afford CH3OH. In this study, a series of molybdenum oxides with different morphologies, including bulk, nanosheet, nanobelt, and rod morphologies, are used as catalysts, and the effects of particle morphologies on the catalytic performance toward CO2hydrogenation are examined. A Pt-loaded molybdenum suboxide nanosheet (Pt/HxMoO3–y(Sheet)) with a high specific surface area affords 1.35 times greater CO2conversion and CH3OH yield in liquid-phase CO2hydrogenation compared with the corresponding bulk analog under relatively mild reaction conditions (total 4.0 MPa, 200 °C). Experiments and comprehensive analyses, including X-ray diffraction and in situ X-ray absorption fine structure studies, reveal that the enhanced activity of Pt/HxMoO3–y(Sheet) is attributable to a high concentration of surface-exposed VOsites, which are introduced in the (010) plane during the H2reduction due to the high surface-to-volume ratio of the nanosheet-structured MoO3. In addition, the nanosheet-structured catalyst exhibits better reusability because of its antiaggregation behavior for Pt NPs compared with the conventional bulk analog.

Published
2023
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119. Enhanced visible-NIR absorption and oxygen vacancy generation of Pt/HxMoWOy by H-spillover to facilitate photothermal catalytic CO2 hydrogenation.

Author

Ge, Hao, Kuwahara, Yasutaka, Kusu, Kazuki, Kobayashi, Hisayoshi, and Yamashita, Hiromi

Abstract

Photothermal catalytic hydrogenation of CO2 is an intriguing approach to reduce CO2 under mild conditions, which is possible because of photoinduced electron–hole pair generation and an overall increase in the localized temperature under light irradiation. However, the lack of a catalyst with an adequate photothermal conversion efficiency and the ability to generate a sufficient number of photoinduced electrons are the main factors limiting the applicability of this method. H-doped WOy demonstrates surface plasmon resonance (SPR) capabilities, and can be adjusted by changing the dopant (H+) concentration. To improve the potential of the WOy plasmonic effect based on H-doping, we herein report that the Mo-doped Pt/WOy (Pt/MoWOy) substantially increases the dopant (H+) and oxygen vacancy concentration in Pt/HxMoWOy during the H2 reduction process, facilitating photothermal hydrogenation of CO2 to CO. The developed Pt/HxMoWOy exhibits excellent catalytic performance (3.1 mmol h−1 g−1) in the photothermal reverse water-gas shift (RWGS) reaction at 140 °C, outperforming undoped Pt/HxWOy (1.02 mmol h−1 g−1). Experimental and comprehensive analyses, including photoelectrochemical measurements, UV-Vis-NIR diffuse-reflectance spectroscopy, and a model reaction, showed that abundant surface free electrons and oxygen vacancies (VO) in Pt/HxMoWOy are responsible for the efficient CO2 adsorption and transfer of photoinduced electrons to carry out the reduction of CO2 to CO. X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption fine structure (XAFS) measurements revealed a reversible redox event for the Mo and W atoms during the RWGS reaction, confirming that the oxygen vacancies between Mo and W atoms in Pt/HxMoWOy act as active sites and that Pt nanoparticles activate H2 to enable the regeneration of the oxygen vacancies. Moreover, density functional theory (DFT) calculations demonstrated that Mo-doping substantially decreases the energy barrier for oxygen vacancy formation in WOy in the H2 reduction process. We expect that this study will provide an innovative strategy for designing a highly efficient catalyst for photothermal CO2 conversion. [ABSTRACT FROM AUTHOR]

Published
2022
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