理論計算探討M/N2O,MO/N2O,MN/NO2(M=Ru、Mo、W)脫氮反應之反應機構

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2011

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本論文分為兩大主題: 一. 探討Ru系列分解NOx。從石化燃料燃燒產生的NOx因具有毒性,故引起科學家關注。本文研究的目的是尋找使NOx轉變成無污染性之氣體N2,且低能障的反應路徑。透過理論計算的方式來探討其可能之反應機制。本主題共可分為兩部分進行探討: 第一部分: 探討Ru原子與N2O分子之反應機制。本文參閱參考文獻,利用計算不同重態之Ru對N2O之分解反應,做理論計算。關於Ru原子和N2O之反應機制乃利用B3LYP/[LanL2DZ + aug-cc-PVTZ]的計算方式來探討。結果顯示Ru + N2O最可行之反應路徑是Ru insertion 到N2O分子,形成ORu(η1-NN),而後再經反應分解產生 RuO+N2。此反應可視為無能障(反應最高能量位置相對於反應物為-68.87 kcal/mol) ,可將N2O轉變為穩定、無毒之氮氣(N2)分子,且放熱67.06 kcal/mol。 第二部分: 探討RuO分子與N2O分子;RuN分子與NO2分子之反應機制。利用RuO/N2O、RuN/NO2進行反應,可產生相同之中間產物,又此中間產物隨後可再分解成無毒的N2,且放熱效果相當好。此部分之反應機制利用B3LYP/[LanL2DZ + aug-cc-PVTZ]的計算層級來探討。結果顯示RuO + N2O最可行之反應路徑是生成RuO2 + N2之產物,反應最高能量位置僅16.11 kcal/mol ,且放熱65.74 kcal/mol。而RuN + NO2最可行之反應路徑仍是生成RuO2 + N2,反應亦可視為無能障(反應最高能量位置相對於反應物僅- 32.21 kcal/mol ),放熱115.89 kcal/mol。 二.探討MoN/WN分解NO2分子及Mo、W多步驟分解N2O。 利用上一主題找出之最佳反應路徑,將Ru改成Mo、W,進一步做相關之理論計算及比較。由能量計算可知WN反應性優於MoN。(MoN放熱139.19 kcal/mol;而WN放熱170.41 kcal/mol) ;而在M+N2O(M=Mo、W)生成N2的反應中,W反應性優於Mo。但若考慮H2還原之能量,則Mo才是較好的選擇。因MoO3利用H2還原成金屬僅需吸熱44.47kcal/mol,WO3卻需吸熱113.29 kcal/mol。
This thesis contains following two major subjects: First: Decomposition of NOx by Ru series. The toxicity of NOx causes scientist's attention. The purpose of this study is to find the way to decompose NOx into non-polluting gas N2, and calculate the lower energy barrier of the reaction paths. We try to investigate the possible reaction mechanism by the theoretical calculations, which include two parts as follows: Part I: The reaction mechanisms of N2O with Ru atom. We try to calculate the decomposition of N2O by Ru atom with different states . The reaction mechanisms of N2O with Ru atom are studied at the B3LYP / [LanL2DZ + aug-cc-PVTZ] level. The result shows that the most feasible mechanism of Ru + N2O is Ru inserted into the N2O molecules, forming ORu (η1-NN), then it decomposed into RuO + N2 (almost without energy barrier). N2O can be transformed into stable, non-toxic gas N2 , and the heat of reaction is -67.06 kcal / mol . Part II: The reaction mechanisms of N2O with RuO molecule and the reaction mechanisms of NO2 with RuN molecule . The metal compounds and NOx molecules , such as RuO/N2O;RuN/NO2 can produce the same intermediates, and then these intermediates can be decomposed into the non-toxic products N2. The result shows that the most feasible reaction path of RuO + N2O is to generate RuO2 + N2, and the highest energy barrier is only 16.11 kcal / mol, with the heat of reaction being -65.74 kcal / mol. On the other hand , the reaction of RuN + NO2 can also generate the products of RuO2 + N2 (almost without energy barrier) , with the heat of reaction being -115.89 kcal / mol. Second: The reaction mechanisms of MoN / WN with NO2 molecules and the multi-step decomposition mechanisms of Mo, W with N2O. Based on the outcome of the first subject , our calculation shows that WN could be better to react with N2O to form N2 (△E of WN is -170.41 kcal / mol as compared to that of MoN, △E = -139.19 kcal / mol) . However, if we consider the △E for the reduction of energy of WO3 and MoO3 to recover W and Mo (△E =113.29 kcal / mol for WO3 and △E =44.47kcal/mol) , then Mo would be more effective than W.

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理論計算, 分解NOx, theoretical calculations, Decomposition of NOx

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