Measured chlorine coverages over Ag/α-AlO catalysts with varying Ag weight loadings (1.3–35 wt%) and different Ag particle size distributions when parsed in terms of Cl coverages over particles of varying size constituted in the distribution reveal that Ag particles of size below ∼30 nm are covered in more than 1 monolayer (ML) of chlorine in presence of 3.5 ppm CHCl. These assessments of Cl coverages were made possible by correlating the cumulative Cl coverage to the lognormal surface area distribution of 22 Ag/α-AlO samples using a single exponential decay function. Fully chlorided small Ag particles exhibit low rates of epoxidation and only large Ag particles which exhibit sub-monolayer Cl coverages catalyze ethylene epoxidation with high ethylene oxide (EO) rates and selectivity. The Ag particle size dependence of Cl coverages plausibly explains why ≥ 100 nm Ag particles are typical in promoted Ag/α-AlO ethylene epoxidation catalysts.

中文翻译：

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氯促进剂在调节银催化乙烯环氧化中粒径效应中的作用


当根据分布中不同尺寸颗粒的 Cl 覆盖率进行解析时，测量具有不同 Ag 重量负载 (1.3–35 wt%) 和不同 Ag 颗粒尺寸分布的 Ag/α-Al2O3 催化剂上的氯覆盖率，表明尺寸的 Ag 颗粒在 3.5 ppm CHCl 存在下，低于 ∼30 nm 的区域被超过 1 个单层 (ML) 的氯覆盖。通过使用单一指数衰减函数将累积 Cl 覆盖率与 22 个 Ag/α-Al2O3 样品的对数正态表面积分布相关联，可以对 Cl 覆盖率进行评估。完全氯化的小银颗粒表现出低环氧化速率，只有表现出亚单层 Cl 覆盖的大银颗粒才能以高环氧乙烷 (EO) 速率和选择性催化乙烯环氧化。 Cl 覆盖率的 Ag 颗粒尺寸依赖性合理地解释了为什么 ≥ 100 nm Ag 颗粒在促进的 Ag/α-Al2O 乙烯环氧化催化剂中是典型的。