本文選題：氧化鎢 + H_2吸附　； 參考：《江西理工大學(xué)》2017年碩士論文

【摘要】：目前許多學(xué)者研究了氧化鎢氫還原制取超細(xì)鎢粉的工藝,但是其機理仍然不統(tǒng)一和明確。關(guān)于氧化鎢表面氫吸附機理和動力學(xué)過程的研究較少,因此有必要對其進(jìn)行研究,從而進(jìn)一步了解氧化鎢氫還原動力學(xué)機理�；趯嶒灄l件的限制,傳統(tǒng)的材料研究設(shè)備都不能被用于研究H原子和H_2分子在氧化鎢表面的吸附狀況,所以人們無法通過實驗的方法來研究H原子和H_2分子與氧化鎢表面的相互作用。針對此問題,本文以Materials Studio7.0軟件為計算平臺,采用第一性原理計算從原子和電子角度探討了氧化鎢表面性質(zhì)及其氫吸附機理,同時采用TG-DSC實驗研究了氧化鎢氫還原的動力學(xué)過程以及動力學(xué)機理,從而為氧化鎢氫還原工業(yè)生產(chǎn)提供一定的理論基礎(chǔ)和指導(dǎo)。研究結(jié)果表明:(1)WO_3晶胞為立方結(jié)構(gòu),而W_(20)O_(58)和W_(18)O_(49)晶胞為單斜不規(guī)則非化學(xué)計量比結(jié)構(gòu)。此三種氧化鎢的晶胞都是由W占據(jù)中心位置以及O占據(jù)頂點位置的八面體組成,其帶隙寬度分別為0.587、0.8、0.75eV,且W_(20)O_(58)晶胞和W_(18)O_(49)晶胞都表現(xiàn)出導(dǎo)電性的金屬行為;WO_3、W_(20)O_(58)和W_(18)O_(49)都表現(xiàn)出電子離域性較強,成鍵強,W和O原子的電子態(tài)密度重疊多,W-O共振較強,共價鍵較多的特性。(2)WO_3(001)、W_(20)O_(58)(010)和W_(18)O_(49)(010)都含有WO終止面和O終止面兩種表面原子結(jié)構(gòu),都是通過改變W-O鍵的鍵長和W-O-W的鍵角來達(dá)到表面弛豫的目的。(3)WO_3(001)四種氫吸附構(gòu)型中,H-O1c-H吸附構(gòu)型的吸附能最小(-3.684eV),H-O鍵最短(0.0968nm),H失去電子數(shù)最多(0.55e),此吸附構(gòu)型最穩(wěn)定。兩個H原子分別與O1c原子形成H-O化學(xué)鍵,且吸附反應(yīng)使得在表面生成了一個H_2O分子結(jié)構(gòu),同時產(chǎn)生了一個表面氧空位。(4)W_(20)O_(58)(010)六種氫吸附構(gòu)型中,O-V-O1c吸附構(gòu)型最穩(wěn)定,其吸附能為-3.11eV,H-O鍵長為0.0983nm,H原子為O原子提供的電子數(shù)為0.55e;H_2分子垂直吸附在W_(20)O_(58)(010)氧終止表面后解離,且兩個H原子與O1c原子形成化學(xué)鍵,最終反應(yīng)生成H_2O分子和產(chǎn)生一個表面氧空位。(5)W_(18)O_(49)(010)四種氫吸附構(gòu)型中,P-O1c、V-O1c兩種吸附構(gòu)型都很穩(wěn)定,吸附能分別為-6.13、-6.807eV,H-O鍵鍵長在0.0978~0.0983nm范圍內(nèi),H原子為O原子提供的電子數(shù)在0.56~0.58e范圍內(nèi);H_2垂直以及水平吸附在W_(20)O_(58)(010)氧終止表面后都會解離,且生成的兩個H原子與O1c形成化學(xué)鍵,反應(yīng)生成H_2O分子和產(chǎn)生一個表面氧空位。(6)氧化鎢氫還原反應(yīng)表觀活化能均小于20 kJ·mol-1且還原體系的失重量隨著時間呈線性變化,H_2的擴散步驟是還原反應(yīng)的限制性環(huán)節(jié),同時還原過程中可能出現(xiàn)晶型的變化,很好地論證了氧化鎢氫還原動力學(xué)機理。
[Abstract]:At present, many scholars have studied the process of producing ultrafine tungsten powder by hydrogen reduction by tungsten oxide, but its mechanism is still not uniform and clear. There are few studies on the mechanism and kinetic process of hydrogen adsorption on the surface of tungsten oxide. Therefore, it is necessary to study it so as to further understand the mechanism of the hydrogen reduction kinetics of tungsten oxide. The traditional material research equipment can not be used to study the adsorption of H atoms and H_2 molecules on the surface of tungsten oxide. So it is impossible for people to study the interaction between H atoms and H_2 molecules on the surface of tungsten oxide. For this problem, this paper uses Materials Studio7.0 software as the computing platform and uses the first principle calculation. The surface properties and hydrogen adsorption mechanism of tungsten oxide are discussed from the atomic and electronic angles. At the same time, the kinetics and mechanism of hydrogen reduction of tungsten oxide are studied by TG-DSC experiment. The theoretical basis and guidance are provided for the industrial production of tungsten oxide hydrogen reduction. The results show that: (1) WO_3 cell is a cubic structure, and W_ (20) ) O_ (58) and W_ (18) O_ (49) cells are monoclinic irregular nonstoichiometric structures. The three tungsten oxide crystals are composed of W occupying center position and eight sides of O occupying the vertex position, the band gap width is 0.587,0.8,0.75eV, and W_ (20) O_ (58) and W_ (18) O_ (49) cells all exhibit conductive metal behavior; WO_3, W_ (2) 0) O_ (58) and W_ (18) O_ (49) show strong electron delimitability, strong bond formation, high overlapping of electron state density of W and O atoms, strong W-O resonance and more covalent bonds. (2) WO_3 (001), W_ (20) O_ (58) (010) and W_ (18) O_ (49) (010) all contain WO terminating surface and two surface atomic structure, all by changing the bond length of the bond bond and In the four hydrogen adsorption configurations of (3) WO_3 (001), the adsorption energy of the H-O1c-H adsorption configuration is minimal (-3.684eV), the H-O bond is the shortest (0.0968nm), the H loses the most electron number (0.55e), and the adsorption configuration is the most stable. The two H atoms form the H-O chemical bond with the O1c atom respectively, and the adsorption reaction makes a H_2O on the surface. The molecular structure produces a surface oxygen vacancy at the same time. (4) W_ (20) O_ (58) (010) six hydrogen adsorption configurations, the O-V-O1c adsorption configuration is the most stable, its adsorption energy is -3.11eV, the H-O bond length is 0.0983nm, the H atom provides 0.55e for O atom, and the H_2 molecule dissociates after the W_ (20) O_ (58) (010) oxygen terminated surface, and two atoms are with the O. C atoms form chemical bonds, and the final reaction generates H_2O molecules and produces a surface oxygen vacancy. (5) in the four hydrogen adsorption configurations of W_ (18) O_ (49) (010), the two configurations of P-O1c and V-O1c are all very stable, and the adsorption energy is -6.13, -6.807eV, and H-O bonds in 0.0978~ 0.0983nm, and the number of electrons provided by H atoms is within the range. H_2 is dissociated vertically and horizontally after the W_ (20) O_ (58) (010) oxygen terminated surface, and two H atoms are formed to form a chemical bond with O1c to produce a H_2O molecule and produce a surface oxygen vacancy. (6) the apparent activation energy of the hydrogen reduction reaction of tungsten oxide is less than 20 kJ. Mol-1 and the weight loss of the reduction system is linearly changed with time, H_ The 2 diffusion step is the limiting link of the reduction reaction. At the same time, the change of crystal form may appear during the reduction process. The kinetic mechanism of the hydrogen reduction of tungsten oxide is well demonstrated.
【學(xué)位授予單位】：江西理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O647.31;TF841.1

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