鐵原子與NO反應(yīng)的密度泛函理論研究

戚越舟， 蘇亞欣

(東華大學(xué)環(huán)境科學(xué)與工程學(xué)院， 上海 201620)

鐵原子與NO反應(yīng)的密度泛函理論研究

戚越舟， 蘇亞欣

(東華大學(xué)環(huán)境科學(xué)與工程學(xué)院， 上海 201620)

采用密度泛函理論(DFT)計(jì)算研究鐵原子與NO反應(yīng)的相關(guān)微觀反應(yīng)機(jī)理.全參數(shù)優(yōu)化了四重態(tài)和六重態(tài)反應(yīng)勢(shì)能面上各駐點(diǎn)的幾何結(jié)構(gòu)，用頻率分析方法和內(nèi)稟反應(yīng)坐標(biāo)(IRC)方法對(duì)過渡態(tài)進(jìn)行了驗(yàn)證，得到了該反應(yīng)的反應(yīng)勢(shì)能面曲線，并討論了勢(shì)能面的交叉情況.結(jié)果表明，該反應(yīng)為典型的兩態(tài)反應(yīng)，反應(yīng)通道一中出現(xiàn)了一個(gè)勢(shì)能交叉點(diǎn)，反應(yīng)通道二中出現(xiàn)了兩個(gè)勢(shì)能交叉點(diǎn)，反應(yīng)通道三中出現(xiàn)了三個(gè)勢(shì)能交叉點(diǎn).勢(shì)能面上的交叉點(diǎn)能夠有效降低反應(yīng)的活化能，增加反應(yīng)放熱，這在動(dòng)力學(xué)和熱力學(xué)上都是有利的.

過渡金屬原子； 量子化學(xué)； 反應(yīng)微觀機(jī)理； 勢(shì)能交叉點(diǎn)

1 引 言

近20年來，探索金屬催化劑的內(nèi)部電子特性，動(dòng)力特性已經(jīng)成為一個(gè)非?；钴S的領(lǐng)域.而過渡金屬由于多相催化的特性而倍受關(guān)注，由此展開了大量的實(shí)驗(yàn)和理論研究[1,2].例如，對(duì)于當(dāng)前煤燃燒過程中排放NOX的環(huán)境污染問題，大量的研究表明金屬能有效促進(jìn)催化還原NO，包括K、Na、Ca等主族金屬以及Cu、Co、Ni、Fe等過渡金屬[3-7].在眾多的過渡金屬中，鐵系催化劑是一種有效脫除氮氧化物的理想催化劑，前期的大量的實(shí)驗(yàn)研究[8-10]表明金屬鐵直接催化還原NO是一種高效的脫硝方法.Blagojevic等[11]研究了Fe+催化CO還原N2O的反應(yīng)路徑，F(xiàn)rancesca Rondinelli等[12]通過DFT理論也得到了Fe+和Mn+催化CO脫除N2O的反應(yīng)路徑，均發(fā)現(xiàn)Fe+能有效降低反應(yīng)的活化能.西北師范大學(xué)王永成等[13,14]研究了Fe+，F(xiàn)eO+消除N2O，發(fā)現(xiàn)鐵系催化劑對(duì)于反應(yīng)的決速態(tài)起關(guān)鍵的作用.但是當(dāng)前絕大多數(shù)關(guān)于鐵系催化劑脫除氮氧化物的量化模擬都集中在鐵離子，鐵的氧化物離子上，對(duì)于鐵原子本身的研究，Andreas Fiedler等[15]研究了Fe、N、O三種元素組成的同分異構(gòu)體，但是缺少了反應(yīng)的路徑和動(dòng)力學(xué)的研究.本文以Fe+NO為研究體系，用密度泛函理論(DFT)計(jì)算方法，研究了反應(yīng)體系在四、六重態(tài)勢(shì)能面上的反應(yīng)機(jī)理，該研究對(duì)于人們理解金屬鐵催化脫硝的重要反應(yīng)提供了理論依據(jù).

2 計(jì)算方法

密度泛函理論(DFT)已廣泛用于過渡金屬化學(xué)的理論計(jì)算，計(jì)算結(jié)果的可靠性已被研究學(xué)者所公認(rèn)[16].文中采用Becke三參數(shù)交換泛函，并結(jié)合LYP相關(guān)泛函(即B3LYP方法)[17]，對(duì)Fe，N，O采用6-31G(d)基組，對(duì)反應(yīng)體系勢(shì)能面上的所有反應(yīng)物、中間體、過渡態(tài)和產(chǎn)物的幾何構(gòu)型進(jìn)行了全參數(shù)優(yōu)化，通過頻率分析證實(shí)了各反應(yīng)物、中間體和產(chǎn)物的能量為局部極小，各過渡態(tài)有唯一振動(dòng)虛頻.對(duì)各勢(shì)能面上的每一個(gè)鞍點(diǎn)進(jìn)行了內(nèi)稟反應(yīng)坐標(biāo)(IRC)計(jì)算，確認(rèn)了每個(gè)基元步驟過渡態(tài)的可靠性.為了獲取更為精確的相對(duì)能量值，在此幾何構(gòu)型基礎(chǔ)上進(jìn)一步采用B3LYP/6-311+G(d,p)方法進(jìn)行單點(diǎn)能計(jì)算.

本文所選用的計(jì)算方法廣泛用于體系中含有過渡金屬的電子結(jié)構(gòu)計(jì)算，Qiao Sun等[18]通過此計(jì)算方法研究鐵簇催化甲烷，Lichen Wang等[19]通過該方法研究了Fe(NO)n+的特性，Q. Sun等[20]通過該方法研究了納米鐵簇的特性，大量的模擬計(jì)算證明這是一種計(jì)算耗時(shí)合理，計(jì)算準(zhǔn)確的方法[21,22].本文所有計(jì)算都在Gaussian 09程序中完成.

3 結(jié)果與討論

本文著重對(duì)脫硝基元反應(yīng)(Fe+NO→FeO+1/2N2)進(jìn)行深入的研究.有過渡金屬參與的反應(yīng)中，高自旋態(tài)過渡金屬?gòu)?fù)合物常常具有多個(gè)未成對(duì)電子，由于受配體與金屬d軌道之間電子的交換作用等因素的影響，導(dǎo)致過渡金屬在催化反應(yīng)過程中很可能發(fā)生自旋翻轉(zhuǎn)而出現(xiàn)勢(shì)能面交叉現(xiàn)象，即在不同自旋多重度的兩個(gè)勢(shì)能面的交叉區(qū)附近出現(xiàn)自旋翻轉(zhuǎn)[23-25].本文以鐵原子與NO的反應(yīng)為研究體系，用密度泛函理論(DFT)計(jì)算方法，研究了反應(yīng)體系在四、六重態(tài)勢(shì)能面上的反應(yīng)機(jī)理，分別優(yōu)化了四重態(tài)和六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的幾何構(gòu)型，得到基元反應(yīng)的微觀進(jìn)程，結(jié)果如圖1～6所示，四重態(tài)的構(gòu)型命名為C，TS，六重態(tài)的構(gòu)型命名為C`，TS`.其中所有的中間體以及過渡態(tài)均為平面結(jié)構(gòu)，鍵角的單位為度，鍵長(zhǎng)的單位為埃.表1為各反應(yīng)過渡態(tài)及中間體振動(dòng)頻率分析的結(jié)果.表2為反應(yīng)通道上各駐點(diǎn)的能量，其中，Eb3lyp表示采用6-311+G(d，p)方法計(jì)算得到的節(jié)點(diǎn)能；Ezpe為零點(diǎn)能;Etotal為各駐點(diǎn)的總能量；Erel為相對(duì)能量.

表1 各反應(yīng)的中間體和過渡態(tài)的振動(dòng)頻率

Table 1 vibration frequency of the intermediates and transition states for each reaction channel

反應(yīng)通道1Reactionchannel1四重態(tài)(cm-1)quartetstates(cm-1)六重態(tài)(cm-1)sextetstates(cm-1)C1199.94381.221386.45C1`269.65469.061422.48TS1-696.7710.9467.0TS1`-269.7574.321469.1C2378.8532.51467.45C2`431.87514.171223.12TS2-167.454591317TS2`-286.8312.591145.2C3`210.23549.981016.65反應(yīng)通道2Reactionchannel2四重態(tài)(cm-1)quartetstates(cm-1)六重態(tài)(cm-1)sextetstates(cm-1)C161.51451.131421.45C1`50.79345.831328.41TS1-181.8368.371350.33TS1`-1941.88487.61284.31C2217.58478.14676.00C2`210.23549.981016.65TS2`-90.21513.65664.96反應(yīng)通道3Reactionchannel3四重態(tài)(cm-1)quartetstates(cm-1)六重態(tài)(cm-1)sextetstates(cm-1)C1199.94381.221386.45C1`269.65469.061422.48TS1-696.7710.9467.0TS1`-269.7574.321469.1C2378.8532.51467.45C2`431.87514.171223.12TS2-632.63448.28844.49TS2`-493.57496.45801.75C3149.60377.15878.39C3`200.13344.99950.82

圖1 反應(yīng)通道一四重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 1 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 1 for quartet state

圖2 反應(yīng)通道一六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 2 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 1 for sextet state

圖3 反應(yīng)通道二四重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 3 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 2 for quartet state

圖4 反應(yīng)通道二六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 4 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 2 for sextet state

圖5 反應(yīng)通道三四重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 5 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 3 for quartet state

圖6 反應(yīng)通道三六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程Fig. 6 Optimized geometrical configurations of various species and micro-reaction pathways in the reaction of channel 3 for sextet state

3.1 反應(yīng)通道一

圖1、2所示為反應(yīng)通道一中Fe原子與NO在四，六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程.首先，鐵原子進(jìn)攻NO的N端生成相應(yīng)的反應(yīng)初始復(fù)合物C1和C1`，此過程無需翻越任何勢(shì)壘.在四重態(tài)反應(yīng)勢(shì)能面上形成Fe，N，O鍵角呈136.1°的中間體C1，屬于Cs點(diǎn)群，電子組態(tài)為4A″，F(xiàn)e-N鍵鍵長(zhǎng)為1.85埃，N-O鍵鍵長(zhǎng)由1.14埃伸長(zhǎng)到1.23埃，鍵級(jí)降低.這表明隨著Fe-N化學(xué)鍵的形成，N-O鍵逐漸變?nèi)?，鍵級(jí)的減小有利于N-O鍵的斷裂.六重態(tài)反應(yīng)勢(shì)能面上也發(fā)生類似的反應(yīng)，形成Fe，N，O鍵角呈135.2°的中間體C1`，屬于Cs點(diǎn)群，電子組態(tài)為6A″，F(xiàn)e-N鍵鍵長(zhǎng)為1.85埃，N-O鍵鍵長(zhǎng)由1.14埃伸長(zhǎng)到1.23埃.接著C1，C1`沿著反應(yīng)路徑，經(jīng)過相應(yīng)的過渡態(tài)TS1和TS1`，生成三角形狀產(chǎn)物復(fù)合物C2和C2`.在這個(gè)過程中，四重態(tài)反應(yīng)勢(shì)能面上C1需要克服8.97 Kcal/mol的勢(shì)壘，F(xiàn)e，N，O鍵角由136.1°減小到73.7°，同時(shí)生成了鍵長(zhǎng)為1.89埃的Fe-O鍵.六重態(tài)反應(yīng)勢(shì)能面上的過程也相似，但是C1`需要克服38.1 Kcal/mol的勢(shì)壘，生成的Fe-O鍵鍵長(zhǎng)為1.91埃.由于四重態(tài)反應(yīng)勢(shì)能面上的勢(shì)壘低，所以反應(yīng)更加容易反應(yīng).最后，C2沿著反應(yīng)路線，經(jīng)過過渡態(tài)TS2，N-O鍵最終斷開生成FeO和1/2的N2.而六重態(tài)勢(shì)能面上的C2`則需再經(jīng)歷一個(gè)過渡態(tài)TS2`生成C3`，N-O鍵鍵長(zhǎng)由1.27埃伸長(zhǎng)至1.31埃，鍵級(jí)降低，F(xiàn)e-O鍵由1.91埃縮短至1.85埃，同時(shí)Fe，O，N的鍵角增大到120°，此過程需要克服17.5Kcal/mol的勢(shì)壘.C`3最終分解成FeO和1/2的N2.從圖7中可以看出，反應(yīng)初始階段六重態(tài)勢(shì)能面上的中間體C1`比四重態(tài)上的中間體C1穩(wěn)定，C1的相對(duì)能量比C1`高4.43 Kcal/mol.初始階段，反應(yīng)更偏向高自旋態(tài).之后六重態(tài)的勢(shì)能面總是高于四重態(tài)，六重態(tài)的能量比四重態(tài)的高，反應(yīng)主要是通過四重態(tài)的反應(yīng)路徑發(fā)生.

3.2 反應(yīng)通道二

圖3、4所示為反應(yīng)通道二中鐵原子與NO在四，六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程.首先，鐵原子進(jìn)攻NO的O端生成反應(yīng)初始復(fù)合物C1和C1`，此過程無需翻越任何勢(shì)壘.在四重態(tài)反應(yīng)勢(shì)能面上形成Fe，N，O鍵角呈179.5°的中間體C1，屬于Cs點(diǎn)群，電子組態(tài)為4A″，F(xiàn)e-O鍵鍵長(zhǎng)為1.83埃，O-N鍵鍵長(zhǎng)由1.14埃伸長(zhǎng)到1.23埃，鍵級(jí)降低.這表明隨著Fe-O化學(xué)鍵的形成，O-N鍵逐漸變?nèi)?，鍵級(jí)的減小有利于O-N鍵的斷裂.六重態(tài)反應(yīng)勢(shì)能面上也發(fā)生類似的反應(yīng)，形成Fe，N，O鍵角呈179.5°的中間體C1`，屬于Cs點(diǎn)群，電子組態(tài)為6A″，F(xiàn)e-O鍵鍵長(zhǎng)為1.91埃，N-O鍵鍵長(zhǎng)由1.14埃伸長(zhǎng)到1.21埃.接著C1，C1`沿著反應(yīng)路徑，經(jīng)過相應(yīng)的過渡態(tài)TS1和TS1`，生成復(fù)合物C2和C2`.在四重態(tài)反應(yīng)勢(shì)能面上，C1需要克服22.1 Kcal/mol的勢(shì)壘，F(xiàn)e，N，O鍵角由179.5°減小到120.1°，F(xiàn)e-O鍵鍵長(zhǎng)由1.23埃伸長(zhǎng)至1.31埃，這個(gè)過程需要克服22.1 Kcal/mol的勢(shì)壘，最終中間體C2的O-N鍵斷裂生成了FeO和1/2的N2；在六重態(tài)反應(yīng)勢(shì)能面上也發(fā)生類似的反應(yīng)，而C1`需要克服6Kcal/mol的勢(shì)壘，相較而言六重態(tài)反應(yīng)勢(shì)能面上此過程更加容易發(fā)生.最后C2`沿著反應(yīng)路徑，經(jīng)過過渡態(tài)TS2`，O-N斷裂，最終生成了FeO和1/2的N2.從圖8中可以看出，反應(yīng)初始階段四重態(tài)勢(shì)能面上的中間體C1比六重態(tài)上的中間體C1`穩(wěn)定，C1的相對(duì)能量比C1`高13.3 Kcal/mol.初始階段，反應(yīng)更偏向低自旋態(tài).之后四重態(tài)的勢(shì)能面總是高于六重態(tài)，四重態(tài)的能量比六重態(tài)的高，反應(yīng)主要是通過六重態(tài)的反應(yīng)路徑發(fā)生.

3.3 反應(yīng)通道三

圖5、6所示為反應(yīng)通道三中鐵原子與NO在四，六重態(tài)反應(yīng)勢(shì)能面上所有駐點(diǎn)的構(gòu)型及反應(yīng)的微觀進(jìn)程.三角形狀產(chǎn)物之前的反應(yīng)大致與反應(yīng)通道一相同.之后C2，C2`沿著反應(yīng)路徑，經(jīng)過相應(yīng)的過渡態(tài)TS2和TS2`，N-O鍵斷裂，在四重態(tài)反應(yīng)勢(shì)能面上N，O的距離為3.38埃，F(xiàn)e-O鍵鍵長(zhǎng)由1.89?？s短至1.65埃，F(xiàn)e-N鍵鍵長(zhǎng)由1.82埃伸長(zhǎng)至1.91埃，鍵級(jí)降低.Fe，O，N之間的鍵角擴(kuò)大至143.1°.這個(gè)過程使N-O鍵徹底斷裂，需要克服47.74 Kcal/mol的勢(shì)壘.最終中間體C3 的Fe-N鍵斷裂生成了FeO和1/2的N2.六重態(tài)反應(yīng)勢(shì)能面上也發(fā)生類似的反應(yīng).復(fù)合物C3`，N，O之間的距離由1.27埃伸長(zhǎng)至2.81埃，F(xiàn)e-O鍵鍵長(zhǎng)由1.91?？s短至1.59埃，F(xiàn)e-N鍵鍵長(zhǎng)由1.82埃伸長(zhǎng)至1.91埃，鍵級(jí)降低.Fe，O，N之間的鍵角擴(kuò)大至106.4°，需要克服68.7 Kcal/mol的勢(shì)壘，相較而言此過程四重態(tài)反應(yīng)勢(shì)能面上更加容易發(fā)生.我們發(fā)現(xiàn)C3和C3`的構(gòu)型變化很大原因很有可能是由于親電子性和極化的作用.從圖8中可以看出，反應(yīng)通道三的反應(yīng)比較復(fù)雜，勢(shì)能面上有多個(gè)交叉點(diǎn)，分別是在不同勢(shì)能面上反應(yīng).

對(duì)反應(yīng)路徑上的所有駐點(diǎn)進(jìn)行了振動(dòng)頻率分析，結(jié)果如表1所示，研究的振動(dòng)分析計(jì)算結(jié)果表明：各反應(yīng)物、產(chǎn)物和中間體的振動(dòng)分析結(jié)果是力常數(shù)矩陣本征值全為正，說明它們?yōu)閯?shì)能面上的穩(wěn)定點(diǎn).各過渡態(tài)的振動(dòng)分析結(jié)果，力常數(shù)矩陣本征值均有且僅有唯一的負(fù)值.同時(shí)采用IRC計(jì)算驗(yàn)證了過渡態(tài)的可信性，結(jié)果表明優(yōu)化得到的中間體和過渡態(tài)都是合理且可信的.

3.4 反應(yīng)勢(shì)能面的交叉點(diǎn)分析

為了更清楚了解Fe與NO的反應(yīng)機(jī)理，我們進(jìn)一步探討反應(yīng)在四重態(tài)和六重態(tài)勢(shì)能面上的交叉行為如圖7～圖9所示.反應(yīng)通道一中：六重態(tài)中間體C1`比四重態(tài)中間體C1的能量低4.43 Kcal/mol,六重態(tài)過渡態(tài)TS1`比四重態(tài)過渡態(tài)TS1的能量高24.7 Kcal/mol；反應(yīng)通道二中：四重態(tài)中間體C1比六重態(tài)中間體C1`的能量低13.3 Kcal/mol，四重態(tài)過渡態(tài)TS1比六重態(tài)過渡態(tài)TS1`的能量高2.1 Kcal/mol，四重態(tài)產(chǎn)物能量比六重態(tài)產(chǎn)物的能量高25.1 Kcal/mol;反應(yīng)通道三中：六重態(tài)中間體C1`比四重態(tài)中間體C1的能量低4.43 Kcal/mol,六重態(tài)過渡態(tài)TS1`比四重態(tài)過渡態(tài)TS1的能量高20.2 Kcal/mol，六重態(tài)中間體C2`比四重態(tài)中間體C2的能量低2.45 Kcal/mol，六重態(tài)過渡態(tài)TS2`比四重態(tài)過渡態(tài)TS2的能量18.5 Kcal/mol，六重態(tài)中間體C3`比四重態(tài)中間體C3的能量高8.9 Kcal/mol.這就大概確定了反應(yīng)可能在反應(yīng)通道一C1`→TS1，反應(yīng)通道二C1→TS1`，C2→反應(yīng)產(chǎn)物，反應(yīng)通道三C1`→TS1,C2→TS2`，TS2`→C3的過程中發(fā)生了“系間竄越”，使得反應(yīng)在不同勢(shì)能面間發(fā)生了翻轉(zhuǎn).反應(yīng)通道一中起初在六重態(tài)勢(shì)能面上進(jìn)行，然后經(jīng)過翻轉(zhuǎn)到四重態(tài)勢(shì)能面進(jìn)行；反應(yīng)通道二起初在四重態(tài)勢(shì)能面上進(jìn)行，然后經(jīng)過翻轉(zhuǎn)到六重態(tài)勢(shì)能面進(jìn)行，最終生成四重態(tài)反應(yīng)產(chǎn)物；反應(yīng)通道三中起初在六重態(tài)勢(shì)能面上進(jìn)行，然后經(jīng)過一次翻轉(zhuǎn)到四重態(tài)勢(shì)能面進(jìn)行，接著第二次翻轉(zhuǎn)到在六重態(tài)勢(shì)能面上，最終生成四重態(tài)產(chǎn)物.根據(jù)Hammond假設(shè)，這是一個(gè)典型的“兩態(tài)反應(yīng)”[25].反應(yīng)通道一中的勢(shì)能交叉點(diǎn)有效的降低活化能24.7 Kcal/mol，同時(shí)增加反應(yīng)放熱29.5 Kcal/mol. 反應(yīng)通道二中的第一個(gè)勢(shì)能交叉點(diǎn)有效降低活化能2.8 Kcal/mol，第二個(gè)勢(shì)能交叉點(diǎn)增加反應(yīng)放熱25.1 Kcal/mol.反應(yīng)通道三中第一個(gè)勢(shì)能交叉點(diǎn)有效降低活化能20.2 Kcal/mol；第二個(gè)勢(shì)能交叉點(diǎn)有效降低活化能18.5 Kcal/mol；第三個(gè)勢(shì)能交叉雖然不能有效降低反應(yīng)活化能但增加反應(yīng)放熱25.1 Kcal/mol.這顯然在動(dòng)力學(xué)和熱力學(xué)上都是有利的.

表2 反應(yīng)通道上各駐點(diǎn)的能量

圖7 Fe+NO在反應(yīng)通道一中四重態(tài)和六重態(tài)的反應(yīng)勢(shì)能面圖Fig. 7 Diagram of PESs for the reaction of Fe+NO on the quartet and sextet states in channel 1

圖8 Fe+NO在反應(yīng)通道二中四重態(tài)和六重態(tài)的反應(yīng)勢(shì)能面圖Fig. 8 Diagram of PESs for the reaction of Fe+NO on the quartet and sextet states in channel 2

圖9 Fe+NO在反應(yīng)通道三中四重態(tài)和六重態(tài)的反應(yīng)勢(shì)能面圖Fig. 9 Diagram of PESs for the reaction of Fe+NO on the quartet and sextet states in channel 3

4 結(jié) 論

本文采用密度泛函理論的B3LYP方法對(duì)金屬鐵與NO的反應(yīng)機(jī)理進(jìn)行了分子水平的模擬研究.分別研究了三個(gè)反應(yīng)通道上四、六重態(tài)反應(yīng)勢(shì)能面上的反應(yīng)，結(jié)果表明金屬鐵原子能有效的把NO轉(zhuǎn)化為FeO和N2，同時(shí)該體系在三個(gè)反應(yīng)通道中進(jìn)行時(shí)，都出現(xiàn)了勢(shì)能交叉點(diǎn)，不僅能有效地降低整個(gè)反應(yīng)過程中的勢(shì)壘，還有利于反應(yīng)動(dòng)力學(xué)和熱力學(xué).本文為進(jìn)一步研究金屬鐵有效催化脫除NO提供了一定的理論依據(jù).

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Density functional theory study of the reaction of iron atom with NO

QI Yue-Zhou, SU Ya-Xin

(School of Environmental Science and Engineering, Donghua University, Shanghai 201620, China)

Density functional theory (DFT) calculations have been carried out to study the micro-mechanism for reaction of iron atom with NO. The geometry optimizations of reactants, transition states, intermediates and products of the reactions of sextet and quartet states were completely optimized, and all the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate calculations. Then the potential energy surface (PES) were obtained and crossing points were investigated. Results showed that the reaction of iron atom with NO was a typical two-state reaction(TSR). One crossing point appeared in the reaction channels 1, Two crossing points appeared in the reaction channels 2, while three crossing points appeared in the reaction channels 3 between the quartet and the sextet potential energy surfaces, which would effectively reduce the activation energy and increase the release of reaction heat, play a significant and beneficial role in the kinetic and thermodynamic aspects of this catalytic reaction.

Transition metal atom; Quantum chemistry; Micro-mechanism of reaction; Crossing point

103969/j.issn.1000-0364.2015.12.005

2014-10-28

國(guó)家自然科學(xué)基金(51278095)

戚越舟(1989—), 男，碩士研究生，主要研究煙氣脫硝及量子化學(xué)模型.

蘇亞欣. E-mail: suyx@dhu.edu.cn

O641

A

1000-0364(2015)06-0924-07