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<p>In this study, nanostructured cobalt oxides (CoO<sub>x</sub>) were synthesized hydrothermally from Co(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O and urea at 110&#xa0;°C for 12&#xa0;h, and the effects of washing (water or ethanol) and drying (oven drying or freeze-drying) pretreatments on their physicochemical properties and catalytic performance toward CO oxidation were systematically investigated. The catalysts were characterized using XRD, FTIR, SEM/TEM, BET, TPR, Raman, XPS, and EPR analysis, and their catalytic activities were evaluated in a custom-designed micro-reactor. The results show that pretreatment plays a decisive role in governing CO oxidation efficiency. Among all samples, the ethanol-washed and freeze-dried catalyst (CoO<sub>x</sub> E–F) displayed the highest activity, achieving T<sub>50</sub> and T<sub>100</sub> temperatures of 62&#xa0;°C and 125&#xa0;°C, respectively. The superior performance of CoO<sub>x</sub> E–F is attributed to the efficient removal of residual ions by ethanol washing and the structural preservation afforded by freeze-drying, which together produce highly dispersed nanostructures with large surface area, uniform mesoporosity, weakened Co–O bond strength, abundant Co<sup>3+</sup> species, and a high concentration of oxygen vacancies. These results demonstrate that combining ethanol washing with freeze-drying is an effective pretreatment strategy for optimizing defect formation and enhancing the intrinsic catalytic properties of Co<sub>3</sub>O<sub>4</sub>-based catalysts for low-temperature CO oxidation.</p> Graphical Abstract <p></p>

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Effect of Solvent Washing and Drying Strategies on the Optimization of Cobalt Oxide Catalysts for CO Oxidation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月25日

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  • Chiu-Hung Liu,
  • Shen-Wei Yu,
  • Chih-Wei Tang,
  • Chen-Bin Wang

摘要

In this study, nanostructured cobalt oxides (CoOx) were synthesized hydrothermally from Co(NO3)2·6H2O and urea at 110 °C for 12 h, and the effects of washing (water or ethanol) and drying (oven drying or freeze-drying) pretreatments on their physicochemical properties and catalytic performance toward CO oxidation were systematically investigated. The catalysts were characterized using XRD, FTIR, SEM/TEM, BET, TPR, Raman, XPS, and EPR analysis, and their catalytic activities were evaluated in a custom-designed micro-reactor. The results show that pretreatment plays a decisive role in governing CO oxidation efficiency. Among all samples, the ethanol-washed and freeze-dried catalyst (CoOx E–F) displayed the highest activity, achieving T50 and T100 temperatures of 62 °C and 125 °C, respectively. The superior performance of CoOx E–F is attributed to the efficient removal of residual ions by ethanol washing and the structural preservation afforded by freeze-drying, which together produce highly dispersed nanostructures with large surface area, uniform mesoporosity, weakened Co–O bond strength, abundant Co3+ species, and a high concentration of oxygen vacancies. These results demonstrate that combining ethanol washing with freeze-drying is an effective pretreatment strategy for optimizing defect formation and enhancing the intrinsic catalytic properties of Co3O4-based catalysts for low-temperature CO oxidation.

Graphical Abstract