氧化鎂薄膜負(fù)載鎢氧化物團(tuán)簇的構(gòu)型和電子結(jié)構(gòu)的理論研究
發(fā)布時(shí)間：2018-07-24 16:41
【摘要】：負(fù)載型鎢氧化物和雙金屬鎢氧化物因其廣泛應(yīng)用于烴類的脫氫、加氫、氧化還原等各類催化反應(yīng)而成為催化領(lǐng)域的研究熱點(diǎn)。為了深入研究該類催化劑結(jié)構(gòu)與催化性能之間的構(gòu)效關(guān)系,本論文采用基于第一性原理的分子動(dòng)力學(xué)與量子力學(xué)相結(jié)合的方法,分別對(duì)CrW_2O_9團(tuán)簇負(fù)載在MgO(001)表面和MgO/Ag(001)薄膜以及W_3O_9團(tuán)簇負(fù)載在MgO/Ag(001)缺陷薄膜上的吸附構(gòu)型和電子結(jié)構(gòu)進(jìn)行了系統(tǒng)研究。對(duì)于MgO(001)表面和MgO/Ag(001)薄膜兩種不同類型載體,負(fù)載后的CrW_2O_9團(tuán)簇表現(xiàn)出完全不同的構(gòu)型。當(dāng)CrW_2O_9團(tuán)簇負(fù)載在MgO(001)表面時(shí),CrW_2O_9團(tuán)簇通過形成兩根W-O鍵和四根Mg-O鍵豎直吸附在MgO(001)表面。而在CrW_2O_9/MgO/Ag(001)體系中,CrW_2O_9團(tuán)簇通過四根Mg-O鍵平行吸附在MgO/Ag(001)薄膜上。電子結(jié)構(gòu)研究表明,CrW_2O_9團(tuán)簇負(fù)載在MgO(001)表面時(shí),只有少量電子(0.73 e)通過共價(jià)吸附鍵從表面轉(zhuǎn)移到CrW_2O_9團(tuán)簇上。而當(dāng)CrW_2O_9團(tuán)簇負(fù)載在MgO/Ag(001)薄膜時(shí),團(tuán)簇得到了較多電子(1.72 e),并且團(tuán)簇所得的電子是由于薄膜的隧道效應(yīng),電子從Ag襯底穿過MgO薄膜轉(zhuǎn)移到團(tuán)簇上。進(jìn)一步的研究還發(fā)現(xiàn)CrW_2O_9/MgO/Ag(001)體系的自旋電荷密度主要定域在Cr原子附近,表明Cr位是一個(gè)較強(qiáng)的路易斯酸位�？梢灶A(yù)測(cè),和單金屬鎢氧化物W_3O_9團(tuán)簇相比,摻雜型雙金屬鎢氧化物CrW_2O_9團(tuán)簇可能具有更好的催化活性。當(dāng)W_3O_9團(tuán)簇沉積在MgO/Ag(001)缺陷薄膜時(shí),團(tuán)簇通過形成八根Mg-O鍵負(fù)載在MgO/Ag(001)缺陷薄膜,并且其中一個(gè)端氧原子填補(bǔ)到MgO薄膜的氧缺陷位。此時(shí),與負(fù)載在MgO(001)單晶缺陷表面相比,W_3O_9團(tuán)簇負(fù)載在MgO/Ag(001)缺陷薄膜時(shí)吸附能顯著提高。進(jìn)一步的電子結(jié)構(gòu)研究結(jié)果表明,負(fù)載后W_3O_9團(tuán)簇得到2.74 e。團(tuán)簇得到的電子主要來源于金屬Ag襯底,有兩個(gè)電子的隧道電流自發(fā)地從金屬Ag襯底穿過MgO薄膜轉(zhuǎn)移到W_3O_9團(tuán)簇,少量電子從薄膜缺陷位通過共價(jià)鍵轉(zhuǎn)移到團(tuán)簇。此外,掃描隧道顯微鏡(STM)圖像和高分辨率電子能量損失譜(HREELS)的能譜模擬結(jié)果表明,W_3O_9團(tuán)簇沉積在MgO/Ag(001)缺陷薄膜和負(fù)載在MgO單晶表面所得的STM圖像以及HREELS譜圖性質(zhì)均顯著不同。
[Abstract]:Supported tungsten oxide and bimetallic tungsten oxide are widely used in dehydrogenation, hydrogenation, redox and other catalytic reactions of hydrocarbons. In order to deeply study the structure-activity relationship between the structure and catalytic performance of this kind of catalysts, this paper adopts the method of combining molecular dynamics and quantum mechanics based on the first principle. The adsorption configurations and electronic structures of CrW_2O_9 clusters on MgO (001) and MgO/Ag (001) films and W_3O_9 clusters on MgO/Ag (001) defective films were studied. For MgO (001) surface and MgO/Ag (001) film, the loaded CrW_2O_9 clusters exhibit completely different configurations. When the CrW_2O_9 cluster is loaded on the surface of MgO (001), CrW2O9 clusters are vertically adsorbed on the MgO (001) surface by forming two W-O bonds and four Mg-O bonds. In CrW_2O_9/MgO/Ag (001) system, CrW2O9 clusters are adsorbed on MgO/Ag (001) thin films by four Mg-O bonds. The electronic structure study shows that only a small amount of electrons (0.73e) are transferred from the surface to the CrW_2O_9 cluster by covalent adsorption bond when the CrW _ 2O _ 9 cluster is loaded on the surface of MgO (001). When the CrW_2O_9 cluster is loaded on the MgO/Ag (001) film, a large number of electrons (1. 72 e),) are obtained in the cluster. The electrons obtained by the cluster are due to the tunneling effect of the film, and the electrons are transferred from Ag substrates through the MgO film to the cluster. It is also found that the spin charge density of CrW_2O_9/MgO/Ag (001) system is mainly located near Cr atom, indicating that Cr site is a strong Lewis acid site. It can be predicted that the doped bimetallic tungsten oxide W_3O_9 clusters may have better catalytic activity than monometallic tungsten oxide W_3O_9 clusters. When W_3O_9 clusters are deposited on MgO/Ag (001) defective films, the clusters are loaded on the MgO/Ag (001) defect films by forming eight Mg-O bonds, and one of the oxygen terminal atoms fills in the oxygen defect sites of the MgO films. At this time, compared with that loaded on the surface of MgO (001) single crystal defect, the adsorption energy of W _ (3) O _ (9) cluster on MgO/Ag (001) defect film is significantly increased. The results of further study on the electronic structure show that the W_3O_9 cluster is 2.74 e. after loading. The electrons obtained from the clusters mainly originate from the metal Ag substrates. The tunneling currents of two electrons spontaneously transfer from the metal Ag substrates through the MgO films to the W_3O_9 clusters, and a small amount of electrons are transferred from the defect sites of the films to the clusters by covalent bonds. In addition, the spectral simulation results of (STM) images of scanning tunneling microscope and (HREELS) of high resolution electron energy loss spectra show that the properties of STM images and HREELS spectra of MgO/Ag (001) defective films deposited on MgO/Ag (001) defect films and MgO single crystal surfaces are significantly different from those obtained from high resolution electron energy loss spectrum (HREELS).
【學(xué)位授予單位】：江西師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O641.1;O643.36
[Abstract]:Supported tungsten oxide and bimetallic tungsten oxide are widely used in dehydrogenation, hydrogenation, redox and other catalytic reactions of hydrocarbons. In order to deeply study the structure-activity relationship between the structure and catalytic performance of this kind of catalysts, this paper adopts the method of combining molecular dynamics and quantum mechanics based on the first principle. The adsorption configurations and electronic structures of CrW_2O_9 clusters on MgO (001) and MgO/Ag (001) films and W_3O_9 clusters on MgO/Ag (001) defective films were studied. For MgO (001) surface and MgO/Ag (001) film, the loaded CrW_2O_9 clusters exhibit completely different configurations. When the CrW_2O_9 cluster is loaded on the surface of MgO (001), CrW2O9 clusters are vertically adsorbed on the MgO (001) surface by forming two W-O bonds and four Mg-O bonds. In CrW_2O_9/MgO/Ag (001) system, CrW2O9 clusters are adsorbed on MgO/Ag (001) thin films by four Mg-O bonds. The electronic structure study shows that only a small amount of electrons (0.73e) are transferred from the surface to the CrW_2O_9 cluster by covalent adsorption bond when the CrW _ 2O _ 9 cluster is loaded on the surface of MgO (001). When the CrW_2O_9 cluster is loaded on the MgO/Ag (001) film, a large number of electrons (1. 72 e),) are obtained in the cluster. The electrons obtained by the cluster are due to the tunneling effect of the film, and the electrons are transferred from Ag substrates through the MgO film to the cluster. It is also found that the spin charge density of CrW_2O_9/MgO/Ag (001) system is mainly located near Cr atom, indicating that Cr site is a strong Lewis acid site. It can be predicted that the doped bimetallic tungsten oxide W_3O_9 clusters may have better catalytic activity than monometallic tungsten oxide W_3O_9 clusters. When W_3O_9 clusters are deposited on MgO/Ag (001) defective films, the clusters are loaded on the MgO/Ag (001) defect films by forming eight Mg-O bonds, and one of the oxygen terminal atoms fills in the oxygen defect sites of the MgO films. At this time, compared with that loaded on the surface of MgO (001) single crystal defect, the adsorption energy of W _ (3) O _ (9) cluster on MgO/Ag (001) defect film is significantly increased. The results of further study on the electronic structure show that the W_3O_9 cluster is 2.74 e. after loading. The electrons obtained from the clusters mainly originate from the metal Ag substrates. The tunneling currents of two electrons spontaneously transfer from the metal Ag substrates through the MgO films to the W_3O_9 clusters, and a small amount of electrons are transferred from the defect sites of the films to the clusters by covalent bonds. In addition, the spectral simulation results of (STM) images of scanning tunneling microscope and (HREELS) of high resolution electron energy loss spectra show that the properties of STM images and HREELS spectra of MgO/Ag (001) defective films deposited on MgO/Ag (001) defect films and MgO single crystal surfaces are significantly different from those obtained from high resolution electron energy loss spectrum (HREELS).
【學(xué)位授予單位】：江西師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O641.1;O643.36
【參考文獻(xiàn)】
相關(guān)期刊論文 前3條
1 徐藝軍,李俊{，
本文編號(hào)：2141996
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