Propylene epoxidation by oxygen over Cu-based catalysts is a most ideal and economical process. The unsupported CuOx nanoparticles were synthesized by liquid phase reduction method. The crystalline phase and size of CuOx nanoparticles were characterized by XRD and TEM, respectively. The catalytic performances of CuOx with different pretreatment temperatures and atmospheres were also investigated. The as prepared unsupported CuOx nanoparticles were composed of Cu and Cu2O. With elevating the pretreatment temperatures under N2 atmosphere, the size of CuOx nanoparticles increased gradually from 25 nm to 58 nm. However, the relative content between Cu and Cu2O remained almost unchanged, indicating that the valence state of Cu species in CuOx was kept nearly constant. The C3H6 epoxidation activities showed a first increases and then decreases trend with enhancing the particle size of CuOx. The highest activity of propylene epoxidation was achieved when the particle size of CuOx was 41 nm. The conversion of propylene was 0.14% and the selectivity of propylene oxide was 30% respectively under the reaction temperature of 150 °C. The results indicated that the appropriate CuOx particle size was a key factor for propylene oxide formation on Cu-based catalysts. The C3H6 epoxidation activities showed a first increases and then decreases trend with enhancing the particle size of CuOx. When the CuOx particle size was 41 nm, the formation rate of PO reached maximum. The appropriate particle size of Cu species with low valence state was crucial to the generation of PO for C3H6 epoxidation reaction by O2 on Cu-based catalysts.

中文翻译：

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无载体 CuOx 对丙烯环氧化反应的尺寸效应

氧在铜基催化剂上进行丙烯环氧化是最理想和经济的工艺。通过液相还原法合成无负载的CuOx纳米颗粒。CuOx 纳米颗粒的晶相和尺寸分别通过 XRD 和 TEM 表征。还研究了不同预处理温度和气氛下 CuOx 的催化性能。所制备的无负载CuOx纳米颗粒由Cu和Cu 2 O组成。随着 N2 气氛下预处理温度的升高，CuOx 纳米颗粒的尺寸从 25 nm 逐渐增加到 58 nm。然而，Cu 和 Cu2O 之间的相对含量几乎保持不变，表明 CuOx 中 Cu 物种的价态几乎保持不变。C3H6环氧化活性随着CuOx粒径的增大呈现先增加后减小的趋势。当 CuOx 的粒径为 41 nm 时，丙烯环氧化的活性最高。在150℃的反应温度下，丙烯的转化率为0.14%，环氧丙烷的选择性为30%。结果表明，适当的 CuOx 粒径是在 Cu 基催化剂上形成环氧丙烷的关键因素。C3H6环氧化活性随着CuOx粒径的增大呈现先增加后减小的趋势。当 CuOx 粒径为 41 nm 时，PO 的生成速率达到最大值。