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研究煤焦表面的活性位点是研究煤焦与甲烷作用机理的基础。本文采用量子化学密度泛函理论方法Dmol3程序优化计算了煤焦表面典型含氧官能团（内酯、酸酐、羧基和酚羟基）结构模型的Mulliken电荷、Fukui函数、变形密度等微观参数。得出煤焦表面含氧物种中，氧原子的电荷分布随其所处化学环境的不同，电荷变化较大，其中内酯和酸酐中羰基氧原子上的Mulliken电荷和Fukui指数相对比其它化学环境中氧原子的要大，说明内酯和酸酐羰基结构上的氧活性最大，是发生化学反应的活性位点。本文还进一步采用LST/QST方法对煤焦表面典型含氧官能团结构模型与甲烷作用的过渡态进行了搜寻，且找到了反应的过渡态。同时，动力学的计算表明典型含氧官能团中，内酯结构中羰基上的氧是催化活化甲烷分解的活性位点，其活化能为94.5kJ/mol，与文献报道的相符。因此推测出，假如煤焦表面的含氧官能团对催化活化甲烷分解起作用，那么内酯结构中羰基上的氧是最有可能的活性位点。 验证采用Boehm滴定和XPS实验的方法，对煤焦与甲烷反应前后煤焦表面的结构进行了测定。Boehm滴定的结果和XPS分峰结果表明在煤焦与甲烷作用后，煤焦表面含氧官能团的含量比作用前有所减小，但减小的不是很大，也可以认为煤焦表面含氧结构对甲烷的分解具有催化作用。同时在对煤焦O1s分峰时发现，O1s峰有剩余，有可能与吸附氧和其它的因素有关，还有待进一步的分析验证。 |
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| Activity on the surface of char-char and is on the basis of the mechanism of methane. In this paper, using quantum chemistry methods Dmol3 DFT optimization procedures typical of the char surface oxygenated functional groups (lactone, anhydride, carboxyl and phenolic hydroxyl group) model of Mulliken charge, Fukui function, such as micro-density deformation parameters. CHAR reached the surface oxygen species, the charge distribution of oxygen atoms with the chemical environment in which the different charge larger changes, lactones and anhydride carbonyl oxygen atoms in the Mulliken charge and Fukui index compared to other chemicals in the environment to the oxygen atom, the lactones and anhydride carbonyl oxygen on the structure of the largest, is a chemical reaction of the active site. This paper further use of LST / QST typical method of char surface oxygenated functional groups methane role model and the structure of the transition state for the search, and found the reaction of the transition state. At the same time, the calculation shows that the typical dynamics oxygenated functional groups, lactone structure of the carbonyl oxygen on the catalytic decomposition of methane activation of the active site, its activation energy of 94.5 kJ / mol, in line with previously reported.Therefore the speculation, if the char surface oxygenated functional groups on the catalytic decomposition of methane activation function, then lactone structure of the carbonyl oxygen is the most likely active site. Boehm titration and verified by XPS experimental method, the reaction of methane and coal char char the surface before and after the determination of the structure. Boehm titration results and XPS results show that the peak in the role of methane and coal tar, coal tar surface oxygenated functional groups in the role than before have decreased, but the decrease is not very great, oxygenated surface can be considered CHAR Structure of a catalytic decomposition of methane. At the same time in the sub-CHAR O1s found that residual O1s peak, it is possible with adsorbed oxygen and other related factors, the analysis still needs to be further verified. |
2楼2008-04-21 20:20:34