第陣4卷第5期南昌大學(xué)學(xué)報(bào)(理科版)Vol 34 No 52010年10月Journal of Nanchang University( Natural Science)0ct.2010文章編號(hào):06-0642010-045-07甲醇與金屬離子相互作用的DFT研究羅冬梅,張寧,洪三國(guó),吳歡文,劉芝花(南昌大學(xué)化學(xué)系,江西南昌330031)摘要:采用量子化學(xué)的DFT理論,在B3LYP水平上模擬了光催化H2O還原CO2的目標(biāo)產(chǎn)物CHOH與幾種金屬離子在基態(tài)時(shí)的相互作用,研究發(fā)現(xiàn)相對(duì)高價(jià)的金屬離子在基態(tài)低配位數(shù)時(shí)會(huì)使甲醇分子離解,而高配位且電荷被大部分中和后則不會(huì)使其離解,中間價(jià)態(tài)的離子配位數(shù)達(dá)到4(含)以上則不會(huì)使其離解,低價(jià)離子不會(huì)使其離解。在實(shí)際的反應(yīng)過程中,由于羥基和大量水分子的存在,金屬離子幾乎沒有機(jī)會(huì)以高價(jià)態(tài)和低配位數(shù)與產(chǎn)率很低的甲醇接觸因而使其離解的兒率極小,所以負(fù)載在ToO2上的金屬離子不會(huì)影響目標(biāo)產(chǎn)物甲醇的脫附。關(guān)鍵詞:CH3OH;金屬離子;DFT中圖分類號(hào):0643文獻(xiàn)標(biāo)志碼:A近年來由于人類活動(dòng)增加了大氣中CO2的濃過程中活性組分與反應(yīng)物分子及產(chǎn)物分子的相互作度,進(jìn)一步加劇了溫室效應(yīng)。溫室效應(yīng)氣體是導(dǎo)致用,既可以節(jié)省篩選催化劑的時(shí)間又可以解釋活性全球變暖的主要原因。解決這一問題的最有效手段物種的作用,研究活性物種對(duì)產(chǎn)物的影響,尤其是對(duì)是將CO2還原為CH3OH等有機(jī)產(chǎn)物。為了實(shí)現(xiàn)這產(chǎn)物穩(wěn)定性的影響,從而研究其脫附的難易,并為反轉(zhuǎn)化,人們進(jìn)行了很多方面的研究,其中最有應(yīng)用應(yīng)機(jī)理的探討提供一定依據(jù)。本文選取負(fù)載于二氧前景的是光催化還原。在還原CO2中催化劑的研化鈦的幾種金屬離子,研究其與產(chǎn)物分子的相互作究是至關(guān)重要的。目前研究最多的是半導(dǎo)體光催化用(CH2OH)m-M-(OH)n,m=1-4,n=2-3)劑1-3。二氧化鈦這類材料禁帶能級(jí)間隔適中、穩(wěn)研究負(fù)載的金屬離子對(duì)產(chǎn)物CH3OH的影響,未見定性好,用其作為光催化劑光解水制氫和光催化還文獻(xiàn)報(bào)道。原CO2的研究十分廣泛。在TO2表面負(fù)載某些金屬或氧化物可以提高光能利用率、增加催化選1計(jì)算細(xì)節(jié)擇性-11。為提高CO2還原反應(yīng)的轉(zhuǎn)化效率,人們采用C03程序包,在B3LYP水平上,由于直致力于尋找高催化活性和高選擇性的光催化大的基組對(duì)計(jì)算電子親和力有用而對(duì)鍵長(zhǎng)和鍵角不劑以提高其光催化CO2還原的活性及產(chǎn)物的選擇是很有用,因而OC和H選取6-31C"基組性;同時(shí)運(yùn)用ESR、氘代示蹤、XPS、AES(俄歇電子金屬離子選取LANL2DZM基組,稀土金屬離子N能譜)等多種手段對(duì)反應(yīng)和催化劑進(jìn)行跟蹤檢測(cè),和Ce采用 Stuttgart RSC19 ECP EMSL基組進(jìn)以期對(duì)反應(yīng)機(jī)理有較為深入的理解,從而為提高光行幾何優(yōu)化和熱力學(xué)計(jì)算研究。本文所用的B3LYP催化CO2的還原效率提供理論基礎(chǔ)。計(jì)算機(jī)科方法即是將包含梯度修正的 Becke交換泛函和包含學(xué)的飛速發(fā)展和量子化學(xué)計(jì)算方法的不斷改進(jìn)推動(dòng)梯度修正的Le、Yang和Pam相關(guān)泛函聯(lián)系在一起,計(jì)算化學(xué)的進(jìn)步,用量子化學(xué)的方法對(duì)材料的化學(xué)局域相關(guān)泛函是用 Vosko、Wk和 Nusair(wWN)局域性質(zhì)和電子結(jié)構(gòu)進(jìn)行表征已經(jīng)取得了顯著成果。自旋密度處理得到的 Becke三參數(shù)泛函為深人了解反應(yīng)的微觀過程和機(jī)理,研究反應(yīng)EKLYP=EIDA +Co(EHF-ELDA )+CxAERS +EVWN物和產(chǎn)物與催化劑及其表面負(fù)載金屬離子的相互作+cc(Em-Ew)(1)用,了解反應(yīng)物的活化和產(chǎn)物的脫附情況,實(shí)驗(yàn)化學(xué)家和理論化學(xué)家還有材料物理學(xué)家都在結(jié)合計(jì)算2結(jié)果與討論機(jī)技術(shù)的發(fā)展而進(jìn)行著多種計(jì)算研究。采用簡(jiǎn)化的2.1中國(guó)煤化工范德華模型體系,理論上定性研究預(yù)測(cè)光催化反應(yīng)CNMHG基本參數(shù),是對(duì)收稿日期:2010-03-10奢需:梅(8學(xué)簿助,931生導(dǎo)師.教,E-m,nzhang@ncu.edu.cn5645南昌大學(xué)學(xué)報(bào)(理科版)2010年化合物一切靜態(tài)和動(dòng)態(tài)性質(zhì)進(jìn)行理論研究的出發(fā)點(diǎn)。計(jì)算結(jié)果表明沒有虛頻,說明得到的結(jié)構(gòu)都是0.657穩(wěn)定的勢(shì)能面上的最低點(diǎn)。在B3LYP水平上采用6-311g…(2)基組計(jì)算得到甲醇分子的鍵長(zhǎng)為C-H:1.091和1.099(2個(gè)C-H等長(zhǎng)度)A,C110.7720:1.421,0-H:0.961A,鍵角H-C-H:108008°,0-C-H:106.900°和112.570°,C-0-2CH.- NdH:107.843°。圖1CH3-OH-Nd-20H和2CH2-OH-Nd的優(yōu)化2.1.1釹離子與甲醇分子的相互作用釹離子與幾何結(jié)構(gòu)(出自 Gaussview4.l,已購(gòu)買版權(quán))甲醇分子的相互作用考慮了2種情況:一種是在欽2.1.2鈰離子與甲醇分子的相互作用(CH2OH)離子結(jié)合2個(gè)氫氧根之后與甲醇分子的相互作用;另一種是釹離子直接在低配位數(shù)情況下與甲醇分子m-Ce-(OH)n的幾何結(jié)構(gòu)參數(shù)基本呈現(xiàn)與釹離的相互作用,在我們的反應(yīng)體系里,負(fù)載在二氧化鈦?zhàn)右恢碌囊?guī)律。上的稀土金屬離子很少量,反應(yīng)前溶液中加入一定量0.2mo/L的氫氧化鈉溶液,而且在光催化反應(yīng)條件下,水分子捕捉光生空穴而形成大量的羥基在催化劑表面,因而負(fù)載離子在低配位情況下與甲醇i0732.038分子直接作用的幾率很小,所以負(fù)載離子不至于使其2.414892033離解,即第一種極端的情況是在理論上模擬的。從結(jié)構(gòu)參數(shù)看,當(dāng)釹離子結(jié)合2個(gè)氫氧根后再110.0902.0J4結(jié)合1個(gè)甲醇分子,即CH3-OH-Nd-20H中,甲醇的幾何結(jié)構(gòu)參數(shù)基本沒有大的改變,Nd-0鍵的鍵長(zhǎng)2242A遠(yuǎn)遠(yuǎn)大于釹離子與氫氧根中的氧的鍵長(zhǎng),因而甲醇分子沒有解離。而低配位時(shí)直接結(jié)合2分子甲醇則發(fā)生了甲醇分子離解的情況,C-0鍵CH,-OH-Ce-30H的鍵長(zhǎng)1.787A,已經(jīng)處于解離狀態(tài)在低配位高電荷的模擬狀態(tài)下,甲醇的羥基被金屬離子剝奪,而實(shí)際的反應(yīng)中這樣的幾率是極其微小的,因而甲醇的脫附不會(huì)受到負(fù)載離子的影響。1.7059CH,-OH-Co4圖2CH-OH-Ce-3OH的CH,-OH-Ce-4的優(yōu)化幾何結(jié)構(gòu)(出自 Gaussview4.1,已購(gòu)買版權(quán)特別的是Ce的電荷比較高,當(dāng)配位數(shù)一致時(shí),電荷因由七機(jī)和,即結(jié)合了3個(gè)氫沒有活化作用而電有CNMHG甲醇分子被解H,-OH-Nd-2OH離羥基被Ce剝奪。對(duì)于高價(jià)負(fù)載離子而言,配位第5期羅冬梅等:甲醇與金屬離子相互作用的DFT研究457數(shù)和電荷都會(huì)對(duì)與之接觸的分子有很大的影響。2.1.3鈦與甲醇的相互作用T與甲醇的相互作1087用中,由于T也是正4價(jià)離子,而且其離子半徑更小,因而在電荷未被飽和的情況下對(duì)甲醇的離解比10.925Ce更徹底,從其C-0鍵的鍵長(zhǎng)也可證明這一點(diǎn)2.010CH,-OH-7n-4圖4CH,-OH- Zn and CH-OH-zn-4的優(yōu)化3OH-CH3-OH-節(jié)幾何結(jié)構(gòu)(出自 Gaussview4.l,己購(gòu)買版權(quán))CH,-OH-Cul4CH,-OH-Ti0.951圖330H-CH3-OH-T和4CH1-OH1-T的優(yōu)化幾何結(jié)構(gòu)(出自 Gaussview4.l,已購(gòu)買版權(quán)同樣當(dāng)電荷大部分被飽和之后,其與甲醇相互作用時(shí)便不致使其離解,基本處于物理作用的范疇。2.1.4鋅與甲醇的相互作用二價(jià)離子Zn,Fe,Ni的情況與高價(jià)離子不同之處在于不必飽和部分電荷,只需配位數(shù)達(dá)到4及其以上時(shí),離子與甲醇相互作用時(shí)就不會(huì)使其離解,只是稍微發(fā)生一點(diǎn)幾何結(jié)0970構(gòu)變化,Zn離子與4個(gè)甲醇分子作用的幾何結(jié)構(gòu)參數(shù)列如圖4,作用的結(jié)果使得C-0鍵的鍵長(zhǎng)比甲醇CH,-OH-Al-20H分子的C-0鍵長(zhǎng)長(zhǎng)0.084A配位數(shù)低時(shí)同樣會(huì)使圍5c1-0H-A1-20 H and CH,-OH-cl的優(yōu)化甲醇分子離解,甲醇分子上的羥基被剝奪。幾何結(jié)構(gòu)(出自 Gaussview4.1,已購(gòu)買版權(quán))Fe和N離子與甲醇分子作用的情況基本與Zn子和鋁離子與甲醇作用的情況較為特殊,三價(jià)的鋁離子是一致的離子由于半徑很小,電荷很高,即使在電荷被部分中2.1.5銅離子和鋁離子與甲醇的相互作用銅離和之后與甲醇分子作用仍然會(huì)使其結(jié)構(gòu)發(fā)生一定的變化,即不利于甲醇的脫附,從幾何結(jié)構(gòu)數(shù)據(jù)看,甲醇與之作用后C-0鍵長(zhǎng)比其分子增長(zhǎng)了0.091A因而中國(guó)煤化工光催化水還原CO,CNMHG擇鋁離子負(fù)載。中丁時(shí)T用即使在較低的配CH,-OH-Z位數(shù)時(shí)也是比較溫和的,作用的結(jié)果對(duì)甲醇分子的458南昌大學(xué)學(xué)報(bào)(理科版)2010年幾何結(jié)構(gòu)幾乎沒有大的影響,有利于甲醇分子的脫的總能量減去與之結(jié)合的氫氧根和甲醇分子的總能附,因而Cu(I)負(fù)載的TO2的光催化劑很常見銅量得到參與作用的不同狀態(tài)的金屬離子的能量,從離子不但對(duì)反應(yīng)本身有利(活化反應(yīng)物,疏導(dǎo)光生能量的數(shù)據(jù)可以分析體系的相對(duì)穩(wěn)定程度。在釹離電子抑制光生電子與空穴的復(fù)合),對(duì)產(chǎn)物的脫附子的2種結(jié)合態(tài)中,結(jié)合了氫氧根的釹能量為(電也沒有阻礙作用,我們的反應(yīng)體系選擇銅離子負(fù)載子和熱能之和)-1428824.356kJ/mol,而低配位態(tài)在TO2上光催化水還原CO2制取甲醇的能量(電子和熱能之和)為-1347775.115kJ2.2能量分析mol可見中和掉大部分電荷的狀態(tài)在能量上是較甲醇分子的電子和零點(diǎn)能之和經(jīng)過零點(diǎn)能校正為穩(wěn)定的狀態(tài),說明釹離子此時(shí)與甲醇的結(jié)合是不后為-303652.415kJ/mol,電子和熱能之和為牢靠的,而低配位的狀態(tài)在能量上是不穩(wěn)定的,對(duì)甲30363.824 k/mol,電子和熱焓之和為醇分子的影響較大,這一結(jié)果與幾何結(jié)構(gòu)參數(shù)是303631.198k/ml,電子和吉布斯自由能之和為致的。其他的能量項(xiàng)目與電子和熱能之和基本上是303773.188kJ/mol。熱能、定容摩爾熱容和熵的致的。補(bǔ)償總量分別為:142.900kJ/mol-K、36.635kJce的情況與釹離子不同,兩者的能量差分別是mol-K和237.676kJ/mo-K,其來自振動(dòng)的分量1245858.384k/mol和-1242387.471kJ/mol分別為:135.461k/mol-K、11.694kJ/mol-K和在數(shù)值上相差不大,但所體現(xiàn)的規(guī)律與釹離子的6.234kJ/mol-K,熵值來自平動(dòng)和轉(zhuǎn)動(dòng)的分量分別致。為:151.980 kJ/mol-K、79.462kJ/mol-K。-OH2.2.3鈦和甲醇體系的能量由于價(jià)態(tài)和結(jié)合方在B3yp/6-311++g水平上得到的相應(yīng)能量式相近,使得Ce和T的情況有些相近,能量差為分別為:-199414.7413kJ/mol、-199404.239k150940.101k/mol和-147282.7767kJ/mol,ol,-199398.988kJ/mol、-199501.383kJ/mol。同樣是數(shù)值相近,但規(guī)律與釹離子相近。熱能、定容摩爾熱容和熵的補(bǔ)償總量分別為:290162.2.4鋅與甲醇體系的能量二價(jià)離子因?yàn)橹贿xk丿/mol-K、20.786kJ/mol-K和172.205kJ/mol-擇離子與甲醇作用的模型,因而高配位數(shù)態(tài)的能量K,熵值來自平動(dòng)和轉(zhuǎn)動(dòng)的分量分別為:144.084k與低配位數(shù)的能量差就可以說明問題,對(duì)于zn離子mol-K和28.125kJ/mol-K。而言,后者與前者之差為-778542.686kJ/mol,高22.1釹離子和甲醇體系的能量比較金屬離子于前者的能量值,雖然數(shù)值差不大,但體現(xiàn)著與釹與甲醇分子不同的相互作用狀態(tài)時(shí)的能量,用體系鈰鈦等離子狀態(tài)相同的規(guī)律表1CH3-OH-Nd-2OH和2CH3-OH-Nd的熱力學(xué)參數(shù)CH】-OH-Nd-2OH2CH,-OH-NdEEZ'2131306.254k/mol1955079.945kJ/molEETH2130799.532k/mol-1955032.686kJ/molHETH -2 131 266 872 kJ/ molGETH-2131476.912k/mol1955279.483k/rVibETHCOM246.1660.0003.7203.720238.726292.3990.0003.7203.720284.960k/molCvCO100.0180.00012.47212.47275.074118.9090.0012.47212.472k/moI-K/m-K354.1715.761175.310113.98959.107420.7135.761175.19211.102126.658a電子和零點(diǎn)能之和經(jīng)過零點(diǎn)能校正后,b電子和熱能之和c電子和熱焓之和,d電子和吉布斯自由能和,e補(bǔ)償?shù)臒崃W(xué)能、定容摩爾熱容和熵值包括總量、電子獻(xiàn)轉(zhuǎn)動(dòng)的和振動(dòng)的貢獻(xiàn),補(bǔ)償?shù)臒崃W(xué)能,g補(bǔ)償?shù)亩ㄈ菽枱崛?h補(bǔ)償?shù)撵刂抵袊?guó)煤化工2.22鈰離子和甲醇體系的能量CNMHG第5期羅冬梅等:甲醇與金屬離子相互作用的DFT研究459表2CH3-OH-Ce-3OH的CH2-OH-Ce-4的熱力學(xué)參數(shù)CH、-OH-Ce-3oHCH -- Ce-42147755.023kJ/mol-2456997.132k/mol2456899.988k/molH-2147689.386kJ/mol-2456894.737k/mol-2147965.063k/mol-2457267.559k/mol268.6380.0003.7203.720261.203586.7560.0003.7203.720579.321k/mol -K151.4650.00012.47212.472126.520242.6130.00012.47212.472217.668kl/mol -K461.5505.761176.180120.717164.653623.7550.000178.477131.281313.99表330H-CH3-OH-T的4CH3-OH-T的熱力學(xué)參數(shù)30H-CH-OF4CH, -OH-Ti1052836.740kJ/mol1361892.438k/m-1052784.230k/mol1361797.920k/mol1052778.979kJ/mol1361792.669k/me1053025.776kmolEle275.8180.0003.7203.720268.378585.1660.0003.7203.720577.731kI/ mol-K2.2420.00012.47212.472117.537242.4210.00012.47212.472217.476k/mol -K415.0320.000169.548116.905128.578582.7480.000173.234129.009280.504k/mol-K表4CH3-OH-Zn的CH,-OH-zn-4的熱力學(xué)參數(shù)CH,-0H-ZnCH,-OH-Zn-4-777502.987k/mol-1385847.517k/mol777455.728k/mol-1384810.444k/mol-777450.477k/mol-777692.023k/mol-1385162.261kJ/molEle306.1100.0003.7203.720298.675613.6300.0003.7203.720606.195kI/mol -K1129340.00012.47212.47287.990228.5130.00012.47212.472203.572k/mol-K404.1870.000169.255113.240121.692606.5500.000174.318128.453298.779k丿mol-K225鋁離子和銅離子甲醇體系的能量幾種金屬離子(負(fù)載在TO2上)在基態(tài)時(shí)的相互作對(duì)于鋁離子和銅離子與甲醇作用的能量態(tài),不用情況的研究發(fā)現(xiàn),相對(duì)高價(jià)的金屬離子在基態(tài)低必做比較,因?yàn)樗鼈兪俏ㄒ坏呐湮粦B(tài)研究模型。配位3結(jié)論分中中國(guó)煤化工位且電荷被大部態(tài)的離子只要配位數(shù)CNMHG離解,低價(jià)離子不對(duì)光催化H2O還原CO2的目標(biāo)產(chǎn)物CH2OH與會(huì)使其離解,幾何結(jié)構(gòu)數(shù)據(jù)和能量數(shù)據(jù)得到了同樣460南昌大學(xué)學(xué)報(bào)(理科版)2010年表5CH,-OH-A-20H和CH,-OH-Cu1的熱力學(xué)參數(shù)CH, --- 2OHCH, -OH-Cul-706323.007k/mol864 kJ/mol706280.999kJ/mol979k/m-706275.748k/mol728 kJ/mol706491.039 kI/moll122210.375 k/molTraTot38.9480.0003.7203.720213.509307.1720.0003.7203.720299733k/mol -Kl12.5160.00012.47212.47287.575114.4950.00012.47212.47289.554k//mol -K361.3470.000165.276112.03584.036405.1320.000169.159112.876123.097kI/mol -K的規(guī)律。在實(shí)際的反應(yīng)過程中,由于羥基和大量水[6] WANG C M. 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Ab initio effective core potentials forInteraction Between CH, OH and Matel lons: Theorital StudiesLUO Dong-mei, ZHANG Ning, HONG San-guo, WU Huan-wen, LIU Zhi-huaAbstract: The interaction between several kinds of metal ions loaded on TiO, and the target product CH, OH in thehotoreduction of CO2 with H,O has been calculated with DFT at B3LYP level. The results revealed that metal ionsat the ground state and low coordinate number dissociated CH, OH by seized its hydroxyl radicals, while metal ionsat hyper coordinate number and the most part of charge neutralized affected the geometry structure of CH, oh littleLow valence metal ions and intermediate valence metal ions which coordinate number is 4 or upwards have no mucheffect to CH, OH. In the practical reaction, there is almost no opp中國(guó)煤化工 coordinate number metal ions to touch low yield CH,OH, therefore the probabilityCNMHGnimal and metalions loaded on TiO, have no resistance to the desorption of CH,OKey words: CH, OH; metal ions; interaction DFT