The intrinsic activity of active sites in catalysts remains a controversial issue, regarding structural sensitivity reactions. Herein, Cu nanoparticles with a broad size distribution were effectively synthesized by tuning the Cu/Al molar ratios of Cu–Al spinel catalysts. The product distribution was found to have a strong dependence on the size of the Cu nanoparticles. It was observed that large Cu nanoparticles were conducive to CO dissociation and CH_x* formation, thereby promoting the insertion of CH_x* into CH_xO*/CO* species, which enhanced the carbon chain growth capacity for synthesizing ethanol. Conversely, the smaller Cu nanoparticles facilitated the HCOO* and CH₃O* intermediates formation, and the CH₃O* was hydrogenated to CH₃OH, which is then dehydrated to produce dimethyl ether (DME). The results revealed that the Cu₁Al₁ catalyst achieved a superior ethanol fraction (24.86%) attributable to the presence of appropriately sized Cu nanoparticles (24.9 nm), which effectively boosted the C–C coupling. However, the Cu₁Al₃ catalyst demonstrated higher DME selectivity (43.98%) as a result of the stronger synergism between smaller Cu nanoparticle size (15.9 nm) and a Cu–Al spinel surface containing acidic sites. Additionally, the larger specific surface area improved the dispersion of Cu species, thereby enhancing the hydrogenation capacity of CO. This work greatly broadens understanding of the intrinsic activity of Cu nanoparticle size, providing an efficient strategy for improving the selectivity of desired products.

中文翻译：

---

Cu-Al 尖晶石催化剂中的 Cu 纳米粒子对 CO 加氢产物分布的尺寸影响


关于结构敏感性反应，催化剂中活性位点的固有活性仍然是一个有争议的问题。在此，通过调节铜铝尖晶石催化剂的铜/铝摩尔比，有效合成了具有宽尺寸分布的铜纳米颗粒。发现产物分布对铜纳米粒子的尺寸有很强的依赖性。观察到大的Cu纳米粒子有利于CO解离和CH _x *的形成，从而促进CH _x *插入CH _x O*/ CO*物种，增强了合成乙醇的碳链增长能力。相反，较小的 Cu 纳米粒子有利于 HCOO* 和 CH ₃ O* 中间体的形成，并且 CH ₃ O* 被氢化为 CH ₃ OH，这然后脱水生成二甲醚(DME)。结果表明，Cu ₁ Al ₁ 催化剂由于适当尺寸的 Cu 纳米粒子（24.9 nm）的存在而获得了优异的乙醇分数（24.86％），这有效地提高了 C –C耦合。然而，由于较小的铜纳米颗粒尺寸（15.9 nm）和铜铝尖晶石之间更强的协同作用，Cu ₁ Al ₃ 催化剂表现出更高的 DME 选择性（43.98%）表面含有酸性位点。此外，更大的比表面积改善了Cu物种的分散性，从而增强了CO的加氢能力。这项工作极大地拓宽了对Cu纳米颗粒尺寸的内在活性的理解，为提高所需产物的选择性提供了有效的策略。