本文選題：釕羰基化合物　切入點：銅摻雜團簇　出處：《山西師范大學》2017年碩士論文　論文類型：學位論文

【摘要】：水煤氣轉(zhuǎn)化反應(yīng)(CO+H_2O→CO_2+H_2)是一個重要的工業(yè)反應(yīng),常應(yīng)用于燃料電池和工業(yè)生產(chǎn)中,而燃料電池的一個重要研究課題是氫氣的來源問題。目前,氫氣的主要來源是水蒸氣重整后的富氫氣體,但是富氫氣體中往往含有大量的CO,CO_2等雜質(zhì)氣體。水煤氣轉(zhuǎn)化反應(yīng)(WGSR)不僅能降低富氫氣體中CO的含量,而且能額外產(chǎn)生氫氣。因此本文主要對釕羰基化合物與銅及其金屬摻雜團簇催化WGSR進行了詳細地研究,并在最后一部分探究了銅摻雜團簇對逆水煤氣轉(zhuǎn)化反應(yīng)(RWGSR)的催化。文中全部構(gòu)型的優(yōu)化和計算都是運用密度泛函理論(DFT)在Gaussian 09程序包運算下完成的,主要內(nèi)容包括有:1.詳細地研究了兩種釕羰基化合物Ru_3(CO)_(12)與Ru(CO)_5在氣相與液相中催化WGSR的機理。其中Ru_3(CO)_(12)和Ru(CO)_5均采取的是D_(3h)對稱構(gòu)型。之前由Torrent,Barrows,Rozanska和Zhang四個課題組陸續(xù)提出Fe(CO)_5催化WGSR的四種反應(yīng)機理,我們將它們運用到Ru_3(CO)_(12)和Ru(CO)_5催化WGSR的計算中,并且將四種機理稱作mechanism A-D。計算發(fā)現(xiàn):Mechanism A由于在OH~-解離時需要較高的反應(yīng)能壘而使反應(yīng)難以發(fā)生。Mechanism B中沒有涉及到Fe(CO)_4H~-這一在實驗中觀察到的重要中間體。Mechanism C與mechanism D克服了以上機理的缺點與不足,但mechanism D與mechanism C相比,前者催化WGSR的反應(yīng)能壘更低。我們首次通過能量跨度模型(Energetic Span Model,ESM)計算轉(zhuǎn)換頻率(turnover frequency,TOF),以用于分析比較催化性能。對四種反應(yīng)機理進行TOF值的計算與比較,發(fā)現(xiàn):mechanism B具有最大的TOF值(3.11×10~(-12)s~(-1),Ru_3(CO)_(12);3.66×10~(-16)s~(-1),Ru(CO)_5),說明在催化WGSR時mechanism B是主反應(yīng)路徑,并且發(fā)現(xiàn)Ru_3(CO)_(12)比Ru(CO)_5對WGSR的催化活性高。在液相中計算Ru_3(CO)_(12)催化WGSR,結(jié)果發(fā)現(xiàn):Ru_3(CO)_(12)在液相中的催化活性比在氣相中的更好,也很好的驗證了實驗中得出的結(jié)果。2.詳細地研究了銅及其摻雜團簇Cu_(12)TM催化WGSR的反應(yīng)機理與催化劑的活性。其中過渡金屬(TM)包括第VIII族中(Co,Rh,Ir,Ni,Pd,Pt)和第IB族(Cu,Ag,Au)共9種。計算了催化WGSR的三種反應(yīng)機理,分別為氧化還原機理,羧基機理,甲酸機理。氧化還原機理的反應(yīng)歷程為:首先,CO和H_2O共同吸附在團簇表面作為中間體1。其次,H_2O分子解離生成OH與H,之后OH再解離生成O和H。接著,生成的O與吸附在團簇表面的CO發(fā)生反應(yīng)生成CO_2。最后,兩個H結(jié)合生成H_2。羧基機理的反應(yīng)歷程前兩步與氧化還原機理相同,然后CO與OH反應(yīng)生成中間物COOH,而COOH再分解生成CO_2和H,最后一步也是兩個H反應(yīng)生成H_2。甲酸機理的前三步與氧化還原機理的前三步是相同的,從第四步開始,生成的H與CO發(fā)生反應(yīng)生成CHO中間物,CHO再與O反應(yīng)生成HCOO中間物,然后HCOO分解生成CO_2和H,最后兩個H結(jié)合生成H_2。通過計算發(fā)現(xiàn):羧基機理為主要反應(yīng)路徑,尤其是在反應(yīng)的最后兩步能壘較低。而氧化還原機理與甲酸機理在催化WGSR時某一步就需要較高的反應(yīng)能壘,比如,OH的再解離以及甲酸機理中HCOO分解產(chǎn)生CO_2這步。因此我們認為羧基機理最適合作WGSR的催化機理。運用ESM模型計算摻雜團簇Cu_(12)TM的TOF值,結(jié)果發(fā)現(xiàn):在d區(qū)金屬靠左側(cè)和右下角位置的Co,Rh,Ir,Ag等金屬摻雜于團簇上表現(xiàn)出更優(yōu)異的催化性質(zhì),例外的是第VIII族的Ni摻雜后表現(xiàn)出最高的催化活性,因為計算得出Cu_(12)Ni最高的TOF值,而TOF值越大對應(yīng)的催化活性越高。3.用銅及其摻雜團簇Cu_(12)TM(TM=Co,Rh,Ir,Ni,Pd,Pt,Cu,Ag,Au)催化逆水煤氣轉(zhuǎn)化反應(yīng)(RWGSR),并對三種反應(yīng)機理進行了詳細地計算。分別為CO_2解離,羧基以及甲酸機理,它們是WGSR三種催化機理的逆反應(yīng),卻又有所不同。通過計算發(fā)現(xiàn):CO_2解離機理是催化RWGSR的最優(yōu)路徑,反應(yīng)歷程為:首先,CO_2和H_2以共吸附的方式吸附在團簇表面Cu_(12)TM。其次,CO_2先解離生成CO和O,之后O被H_2解離生成的2個H連續(xù)氧化先后生成OH與H_2O,最后得到產(chǎn)物CO和H_2O。通過ESM模型計算9種Cu_(12)TM的催化效率,結(jié)果表明:摻雜團簇Cu_(12)Co的TOF值最大(8.92×10~(-13)),說明團簇Cu_(12)Co對催化RWGSR表現(xiàn)出最好的催化活性。此外,我們首次利用d帶中心值(ε_d)分析吸附在團簇表面上的CO_2的活性。團簇中摻雜的過渡金屬(TM)的d帶中心值(ε_d)與費米能級存在線性關(guān)系,ε_d值越靠近費米能級,團簇對CO_2的吸附能越大,催化反應(yīng)更容易進行。這一線性關(guān)系可以作為一種“指針”很好地指示物質(zhì)的催化活性與吸附性能。
[Abstract]:The water gas shift reaction (CO+H_2O, CO_2+H_2) is an important industrial reaction, often used in fuel cell and industrial production, and is an important research topic of the fuel cell is a source of hydrogen. At present, the main source of hydrogen rich hydrogen gas steam reforming after, but often in hydrogen rich gas contains a lot of CO, CO_2 and other impurities in the gas. The water gas shift reaction (WGSR) can not only reduce the content of CO in hydrogen rich gas, and can produce additional hydrogen. So this paper focuses on ruthenium carbonyl compounds and copper and metal doped clusters catalyzed by WGSR were studied in detail, and explores the copper doped clusters transformation the reaction of reverse water gas in the last part (RWGSR) of the catalyst. The calculation and optimization of all configurations in the text are using the density functional theory (DFT) to complete the Gaussian 09 package under the operation, the main content includes: 1. detail Study on two kinds of ruthenium carbonyl compounds Ru_3 (CO) _ (12) and Ru (CO) WGSR _5 in the catalytic mechanism of gas phase and liquid phase. The Ru_3 (CO) _ (12) and Ru (CO) _5 D_ (3H) is adopted. Before the symmetric configuration by Torrent, Barrows, Rozanska four Zhang and group Fe (CO) successively proposed four kinds of reaction mechanism of _5 catalyzed by WGSR, we apply them to Ru_3 (CO) _ (12) and Ru (CO) to calculate the _5 catalytic WGSR, and the four kinds of mechanism called mechanism A-D. Mechanism A calculated that the reaction to Fe involved not to.Mechanism B due to the higher in the OH~- dissociation reaction barrier (CO _4H~-) this was observed in the experiment is an important intermediate of.Mechanism C and mechanism D mechanism to overcome the above shortcomings, but mechanism D and mechanism C, the former WGSR catalytic reaction energy barrier is lower. We for the first time through the energy span model (Energeti c Span Model,ESM)璁＄畻杞崲棰戠巼(turnover frequency,TOF),浠ョ敤浜庡垎鏋愭瘮杈冨偓鍖栨，

本文編號：1613049