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57. Effect of oxygen vacancies and crystal phases in defective Pt/ZrO2−xon its photocatalytic activity toward hydrogen productionElectronic supplementary information (ESI) available: N2adsorption/desorption isotherms, HAADF-STEM images, ESR spectra, XRD patterns, diffuse-reflectance spectra, and DFT calculation models. See DOI: https://doi.org/10.1039/d3cy01470c

Author

Yamazaki, Yukari, Doshita, Naoto, Mori, Kohsuke, Kuwahara, Yasutaka, Kobayashi, Hisayoshi, and Yamashita, Hiromi

Abstract

Among insulating transition-metal oxides, ZrO2has the potential to be a photocatalyst; however, its wide bandgap (∼5 eV) interferes with its ability to absorb sufficient light. Defect engineering—that is, the creation of oxygen vacancies (VOs) and/or Zr3+ions, is a promising strategy for adjusting the bandgap of ZrO2for photocatalytic applications. This study demonstrates that the included VOs play an important role in boosting photocatalytic activity. In addition, the crystal phase of ZrO2(e.g., monoclinic or tetragonal) strongly influences both VOformation and photocatalytic activity. After a Pt cocatalyst was deposited onto ZrO2with a single crystal phase (i.e., monoclinic (m-) or tetragonal (t-)), the specimens were reduced at 200, 400, and 600 °C to obtain photocatalysts with different amounts of VOs. As-synthesized m-ZrO2possessed Zr3+ions in the absence of VOs, and the reduction treatment promoted VOformation accompanied by the disappearance of Zr3+. The as-synthesized t-ZrO2originally included VOs, and their amount in Pt/t-ZrO2−xincreased with increasing reduction temperature. Pt/t-ZrO2−xpossessed a greater amount of VOs than Pt/m-ZrO2−xreduced at the same temperature, suggesting that VOformation occurs more easily in t-ZrO2than in m-ZrO2. Photocatalytic activity increased with increasing reduction temperature, which is the same tendency observed for the VOamount. In a comparison of the crystal phases, Pt/m-ZrO2−xexhibited relatively higher activity than Pt/t-ZrO2−xdespite its fewer VOs, suggesting that the VOformed in the monoclinic ZrO2contributes to the enhancement of the photocatalytic activity more efficiently than in the tetragonal one.

Published
2024
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84. Ru complex and N, P-containing polymers confined within mesoporous hollow carbon spheres for hydrogenation of CO2 to formate.

Author

Yang, Guoxiang, Kuwahara, Yasutaka, Mori, Kohsuke, Louis, Catherine, and Yamashita, Hiromi

Abstract

The development of reliable catalysts with both excellent activity and recyclability for carbon dioxide (CO2) hydrogenation is challenging. Herein, a ternary hybrid heterogeneous catalyst, involving mononuclear Ru complex, N, P-containing porous organic polymers (POPs), and mesoporous hollow carbon spheres (Ru3+-POPs@MHCS) is reported for CO2 hydrogenation to formate. Based on comprehensive structural analyses, we demonstrated that Ru3+-POPs were successfully immobilized within MHCS. The optimized Ru3+-0.5POPs@MHCS catalyst, which was obtained with about 5 wt.% Ru3+ and 0.5 mmol POPs polymers confined into 0.3 g MHCS, exhibited high catalytic activity for CO2 hydrogenation to formate (turnover number (TON) > 1,200 for 24 h under mild reaction conditions (4.0 MPa, 120 °C)) and improved durability, compared to Ru3+ catalysts without POPs polymers (Ru3+-MHCS) and unencapsulated MHCS (Ru3+-0.5POPs) catalysts. The improved catalytic performance is attributed to the high surface area and large pore volume of MHCS which favors dispersion and stabilization of Ru3+-POPs. Furthermore, the MHCS and POPs showed high CO2 adsorption ability. Ru3+-POPs encapsulated into MHCS reduces the activation energy barrier for CO2 hydrogenation to formate. [ABSTRACT FROM AUTHOR]

Published
2023
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