In situ Raman spectroscopy study of silver particle size effects on unpromoted Ag/α-Al2O3 during ethylene epoxidation with molecular oxygen
In situ Raman spectroscopy study of silver particle size effects on unpromoted Ag/α-Al2O3 during ethylene epoxidation with molecular oxygen
复制标题
原位拉曼光谱研究乙烯分子氧环氧化过程中银粒径对未促进的 Ag/α-Al2O3 的影响
DOI：
10.1016/j.jcat.2023.01.016
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发表时间：
2023
影响因子：
7.3
通讯作者：
Bravo-Suárez, Juan J.
中科院分区：
文献类型：
--
作者：
Alzahrani, Hashim A.;Bravo-Suárez, Juan J.
采用原位拉曼光谱和平行固定床反应器研究了不同粒径的Ag/α-Al_2O_3催化剂在1atm、200 ℃、O_2气氛下的乙烯环氧化反应。发现对于20-50 nm的Ag颗粒，重量归一化转化率随着Ag颗粒尺寸的增加而迅速降低，但在50 nm以上几乎保持恒定。另一方面，在20-170 nm的研究范围内，表观TOF随着Ag颗粒尺寸的增加而增加，而在零停留时间下的环氧乙烷选择性几乎恒定（55 ± 4%）。在815（所有Ag尺寸）和880（Ag尺寸> 100 nm）cm-1处的拉曼谱带被识别并归属于活性分子氧物种。880 cm− 1的物种被认为是由表面下氧稳定的分子氧复合物结构。880 cm− 1氧物种的存在可能解释了较大Ag颗粒（>100 nm）中较高的表观TOF。
In situ Raman spectroscopy and parallel fixed bed reactor studies were conducted under ethylene epoxidation conditions with O2at 1 atm and 200 ℃ on unpromoted Ag/α-Al2O3catalysts with different Ag particle sizes. It was found that for Ag particles of 20–50 nm, the weight normalized conversion rate decreased rapidly with increasing Ag particle size but remained almost constant above 50 nm. On the other hand, the apparent TOF increased with increasing Ag particle sizes in the 20–170 nm studied range, while ethylene oxide selectivity at zero residence time was nearly constant (55 ± 4%). Raman bands at 815 (all Ag sizes) and 880 (Ag sizes > 100 nm) cm−1were identified and assigned to active molecular oxygen species. The 880 cm−1species was assigned to a molecular oxygen complex structure stabilized by subsurface oxygen. The presence of the 880 cm−1oxygen species likely explain the higher apparent TOF in larger Ag particles (>100 nm).