本文選題：Cu（111） + Cu/Cr_2O_3催化劑　； 參考：《天津大學(xué)》2011年博士論文

【摘要】：乙酸乙酯（EA）是醋酸的重要下游產(chǎn)品，也是一種重要的綠色有機(jī)溶劑。EA作為一種高檔溶劑，其生產(chǎn)方法的研究一直是關(guān)注的熱點(diǎn)，其中乙醇脫氫法被認(rèn)為是最有應(yīng)用前景的工藝路線。目前Cu-Cr系催化劑對EA的選擇性較高，且已成功應(yīng)用于工業(yè)生產(chǎn)。量子化學(xué)方法可以深入研究反應(yīng)基元步驟中各物種的結(jié)構(gòu)和電子性質(zhì)等，從而為催化劑改性和工藝改進(jìn)提供理論依據(jù)。 本文以Cu和Cu/Cr_2O_3催化劑作為研究體系，試圖深入研究乙醇脫氫制備乙酸乙酯的反應(yīng)機(jī)理，，從微觀角度分析Cu和Cr_2O_3催化劑組分在催化反應(yīng)中的作用，揭示催化劑構(gòu)效關(guān)系。 首先通過表征和實(shí)驗研究分析了Cu-Cr系催化劑的結(jié)構(gòu)。結(jié)果表明，Cu-Cr系催化劑中Cu和Cr元素的存在形式分別是Cu0和Cr_2O_3，催化劑表面的活性中心是Cu0物種。以上實(shí)驗結(jié)果為搭建合理的催化劑模型奠定了基礎(chǔ)，保證了模擬研究的可靠性。 基于實(shí)驗研究結(jié)果，本文構(gòu)建了活性中心Cu的模型，用DFT方法計算了乙醇脫氫反應(yīng)中各個相關(guān)物種（包括CH_3CH_2OH、CH_3CH_2O、CH_3CHO、CH_3CO、CH_3COC2H_5）在Cu（111）面上最穩(wěn)定的吸附位置與構(gòu)型。參照Colley機(jī)理和Kanichiro機(jī)理，對乙醇脫氫制備乙酸乙酯過程中每一步基元反應(yīng)進(jìn)行過渡態(tài)搜索，得到相關(guān)反應(yīng)能壘數(shù)據(jù)。通過對比兩個機(jī)理的計算結(jié)果，認(rèn)為在Cu (111)面上乙醇更傾向于按照Colley反應(yīng)機(jī)理生成乙酸乙酯，乙醇分子斷開O-H鍵脫氫生成乙氧基的能壘最高，反應(yīng)能壘為1.32eV。 通過搭建Cr_2O_3和Cu/Cr_2O_3模型，研究了乙醇在其上的吸附和脫氫過程。研究結(jié)果表明，乙醇分子吸附在Cu/Cr_2O_3催化劑上時，Cu_4團(tuán)簇與Cr_2O_3的交界處提供的活性位最穩(wěn)定，其最穩(wěn)定構(gòu)型的吸附能為0.80eV；乙醇與Cu_4團(tuán)簇之間形成Cu-O鍵，這樣就使得乙醇分子更好地化學(xué)吸附在Cu上，為其下一步脫氫提供有利條件；乙醇在Cr_2O_3(001)表面、Cu(111)表面和Cu/Cr_2O_3體系脫氫生成乙氧基的能壘分別為0.42eV、1.32eV和0.59eV，Cr_2O_3本身也較純銅有較好的脫氫能力；銅和三氧化二鉻的協(xié)同作用在很大程度上增強(qiáng)了乙醇分子在Cu/Cr_2O_3催化劑上的吸附穩(wěn)定性，有效地降低了乙醇脫氫解離為乙氧基這一步的能壘，強(qiáng)化了Cu的活性中心作用，提高了乙醇的轉(zhuǎn)化率。 結(jié)合實(shí)驗和模擬方法，深入研究Cu基催化劑的酸堿性。利用原位吸附吡啶-FT-IR測定方法得出純Cu催化劑表面具有L酸中心，沒有B酸中心；Cu-Cr催化劑具有L酸中心，同時Cr的加入，引入了B酸位，但這些B酸中心的數(shù)量相比L酸來說較少。分子模擬結(jié)果表明當(dāng)有缺電子的分子或基團(tuán)攻擊時，純銅表面和Cr_2O_3(001)面具有親核性，即有L堿中心；而當(dāng)有富電子的分子或基團(tuán)攻擊時，純銅表面和Cr_2O_3(001)面具有親電性，即有L酸中心。在乙醇脫氫過程中會產(chǎn)生很多游離態(tài)的H，銅和Cr_2O_3(001)面可以接受質(zhì)子，因而具有B堿中心；但Cu不具備給出質(zhì)子的能力，沒有B酸中心，而Cr_2O_3(001)面可以給出質(zhì)子，具有B酸中心。且Cr_2O_3表面的酸性強(qiáng)于Cu表面，Cr_2O_3的加入增加了催化劑的Lewis堿性和B酸性，可使催化劑酸堿性質(zhì)更好地匹配。 本文的研究成果對設(shè)計、開發(fā)和改進(jìn)乙醇脫氫法新型催化劑與工藝具有重要的指導(dǎo)意義。
[Abstract]:Ethyl acetate ( EA ) is an important downstream product of acetic acid , and it is an important green organic solvent . As a kind of high - grade solvent , the research of its production method has been a hot spot , in which ethanol dehydrogenation is considered to be the most promising process route . The present Cu - Cr series catalyst has high selectivity to EA and has been successfully applied to industrial production . The quantum chemistry method can further study the structure and electronic properties of each species in the reaction elementary step , thus providing theoretical basis for catalyst modification and process improvement .

In this paper , Cu and Cu / Cr _ 2O _ 3 catalysts were used as the research system to study the reaction mechanism of ethanol dehydrogenation to prepare ethyl acetate . The effects of Cu and Cr _ 2O _ 3 catalyst components in catalytic reaction were analyzed from the micro - angle , and the structure - effect relationship of catalyst was revealed .

First , the structure of Cu - Cr series catalyst was analyzed by characterization and experimental study . The results show that the Cu and Cr elements in Cu - Cr system are Cu0 and Cr2O3 respectively , and the active center of the catalyst surface is Cu0 species . The above experimental results provide the foundation for setting up a reasonable catalyst model , and the reliability of the simulation study is ensured .

Based on the experimental results , this paper constructed a model of active center Cu . The most stable adsorption sites and configurations of various related species ( including CH _ 3CH _ 2OH , CH _ 3CH _ 2O , CH _ 3CHO , CH _ 3CO , CH _ 3CO2H _ 5 ) on Cu ( 111 ) surface were calculated by DFT method .

The adsorption and dehydrogenation process of ethanol on the Cu / Cr _ 2O _ 3 catalyst was investigated by means of establishing the model of Cr _ 2O _ 3 and Cu / Cr _ 2O _ 3 . The results showed that when the ethanol molecules were adsorbed on the Cu / Cr _ 2O _ 3 catalyst , the most stable activity of the Cu _ 4 cluster and the interface of Cr _ 2O _ 3 was 0.80eV .
the Cu - O bond is formed between the ethanol and the Cu _ 4 cluster , so that the ethanol molecule is better chemically adsorbed on the Cu , thereby providing favorable conditions for the next dehydrogenation ;
The surface of Cr _ 2O _ 3 ( 001 ) , Cu ( 111 ) surface and Cu / Cr _ 2O _ 3 system dehydrogenated to form an ethoxy energy barrier of 0.42 eV , 1.32 eV and 0.59 eV , respectively , and the Cr _ 2O _ 3 itself has a better dehydrogenation capability than pure copper .
The synergistic effect of copper and chromium sesquioxide greatly enhances the adsorption stability of ethanol molecules on Cu / Cr _ 2O _ 3 catalyst , effectively reduces the energy barrier of ethanol dehydrogenation and dissociation to ethoxy , strengthens the active center of Cu , and improves the conversion rate of ethanol .

In this paper , the acid - alkali of Cu - based catalyst was studied by using the method of experiment and simulation . Using in situ adsorption of pyridine - FT - IR , it was found that the pure Cu catalyst had an L - acid center and no B - acid center .
The results of molecular simulation show that pure copper surface and Cr _ 2O _ 3 ( 001 ) surface have nucleophilicity , i.e . L - base center , when electron - deficient molecules or groups are attacked .
When an electron - rich molecule or group is attacked , the pure copper surface and the Cr _ 2O _ 3 ( 001 ) surface have an electrophilicity , that is , an L - acid center . In the process of dehydrogenation of ethanol , many free H , Cu and Cr _ 2O _ 3 ( 001 ) planes can receive protons and thus have a B - base center ;
But Cu does not possess the ability to give proton , there is no B acid center , and the surface of Cr _ 2O _ 3 ( 001 ) can give proton , which has the center of B acid . The acidity of Cr _ 2O _ 3 surface is stronger than that of Cu surface . The addition of Cr _ 2O _ 3 increases the Lewis basicity and B acidity of the catalyst , which can better match the properties of catalyst acid and base .

The research results have important guiding significance for designing , developing and improving the new catalyst and process of ethanol dehydrogenation process .
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2011
【分類號】：TQ225.241;TQ426

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