Department of Chemistry, Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario, Canada.
Langmuir. 2012 Mar 6;28(9):4241-7. doi: 10.1021/la204667v. Epub 2012 Feb 22.
Adsorption of CO(2) was investigated on a series of primary, secondary, and tertiary monoamine-grafted pore-expanded mesoporous MCM-41 silicas, referred to as pMONO, sMONO, and tMONO, respectively. The pMONO adsorbent showed the highest CO(2) adsorption capacity, followed by sMONO, whereas tMONO exhibited hardly any CO(2) uptake. As for the stability in the presence of dry CO(2), we showed in a previous contribution [J. Am. Chem. Soc.2010, 132, 6312-6314] that amine-supported materials deactivate in the presence of dry CO(2) via the formation of urea linkages. Here, we showed that only primary amines suffered extensive loss in CO(2) uptake, whereas secondary and tertiary amines were stable even at temperature as high as 200 °C. The difference in the stability of primary vs secondary and tertiary amines was associated with the occurrence of isocyanate as intermediate species toward the formation of urea groups, since only primary amines can be precursors to isocyanate in the presence of CO(2). However, using a grafted propyldiethylenetriamine containing both primary and secondary amines, we demonstrated that while primary amines gave rise to isocyanate, the latter can react with either primary or secondary amines to generate di- and trisubstituted ureas, leading to deactivation of secondary amines as well.
研究了一系列伯、仲、叔单胺接枝的孔扩张介孔 MCM-41 硅石，分别称为 pMONO、sMONO 和 tMONO，对其 CO2 的吸附性能进行了研究。pMONO 吸附剂表现出最高的 CO2 吸附容量，其次是 sMONO，而 tMONO 几乎没有 CO2 吸收。至于在干燥 CO2 存在下的稳定性，我们在之前的一项研究[J. Am. Chem. Soc.2010, 132, 6312-6314]中表明，胺基支持的材料在干燥 CO2 存在下通过形成脲键而失活。在这里，我们表明只有伯胺在 CO2 吸收中遭受广泛损失，而仲胺和叔胺即使在高达 200°C 的温度下也保持稳定。伯胺与仲胺和叔胺的稳定性差异与异氰酸酯作为形成脲基的中间物种的出现有关，因为只有伯胺在 CO2 存在下才能成为异氰酸酯的前体。然而，使用含有伯胺和仲胺的接枝丙二基二乙三胺，我们证明了虽然伯胺会产生异氰酸酯，但后者可以与伯胺或仲胺反应生成二取代和三取代的脲，从而导致仲胺失活。
