The oxidized soot surface: theoretical study of desorption mechanisms involving oxygenated functionalities and comparison with temperature programed desorption experiments.
The oxidized soot surface: theoretical study of desorption mechanisms involving oxygenated functionalities and comparison with temperature programed desorption experiments.
复制标题
氧化烟灰表面：涉及氧化功能的解吸机制的理论研究以及与程序升温解吸实验的比较。
DOI：
--
复制
发表时间：
2006
影响因子：
4.4
通讯作者：
G. Tonachini
中科院分区：
文献类型：
--
作者：
Gianluca Barco;A. Maranzana;Giovanni Ghigo;M. Causà;G. Tonachini
采用量子力学计算方法研究了含氧官能团在煤烟上的解吸机理，并与最近发表的温度程序解吸-质谱分析结果进行了比较。多环芳烃上的取代基逐渐增大（母体多环芳烃中碳原子最多可达46个），以重现氧化石墨烟尘血小板的局部特征。最初，该研究是在单分子破碎（在某些情况下是挤压）过程中进行的，在模型酮、羧酸、内酯、酸酐、一种醛、一种过氧酸、一种过氧化氢、一种仲醇和一种苯酚中产生HO、CO或CO2。然后，考虑了其中一种羧酸的双分子过程。此外，对于其他四种双官能化模型，研究了涉及两个相邻羧基（源自酸酐水解）可能产生的一些协同效应。通过比较计算得到的断裂（解吸）障碍与TPD光谱（HO、CO或CO2解吸）中出现最大值的温度，可以为将这些最大值分配给特定的官能团提供建议，也就是描述氧化表面的关键。值得注意的是，计算表明：(1)由羧基或内酯基团功能化的石墨血小板部分的解吸模式显著依赖于局部的化学和几何环境。因此，我们提出(2)并不是所有的羧基都在通常所说的相对较低的温度下丢失，并且(3)内酯基团可以被确定为不仅产生CO2而且产生CO。
The desorption mechanism for oxygenated functionalities on soot is investigated by quantum mechanical calculations on functionalized polycyclic aromatic hydrocarbon (PAH) models and compared with recently published temperature programed desorption-mass spectrometry results. Substituents on PAHs of increasing size (up to 46 carbon atoms in the parent PAH) are chosen to reproduce the local features of an oxidized graphenic soot platelet. Initially, the study is carried out on unimolecular fragmentation (extrusion, in some cases) processes producing HO, CO, or CO2, in model ketones, carboxylic acids, lactones, anhydrides, in one aldehyde, one peroxyacid, one hydroperoxide, one secondary alcohol, and one phenol. Then, a bimolecular process is considered for one of the carboxylic acids. Furthermore, some cooperative effect which can take place by involving two vicinal carboxylic groups (derived from anhydride hydrolysis) is investigated for other four bifunctionalized models. The comparison between the computed fragmentation (desorption) barriers for the assessed mechanisms and the temperature at which maxima occur in TPD spectra (for HO, CO, or CO2 desorption) offers a suggestion for the assignment of these maxima to specific functional groups, i.e., a key to the description of the oxidized surface. Notably, the computations suggest that (1) the desorption mode from a portion of a graphenic platelet functionalized by a carboxylic or lactone groups is significantly dependent from the chemical and geometric local environment. Consequently, we propose that (2) not all carboxylic groups go lost at the relatively low temperatures generally stated, and (3) lactone groups can be identified as producing not only CO2 but also CO.