Syntheses Of Layered Double Hydroxide(LDH) And The Catalytic Properties Of Au/LDH

This dissertation focus on the in-situ growth of Layered Double Hydroxide (LDH) on matrix and the catalytic properties of LDH supported gold catalysts for alcohol oxidation. The main content and results of this thesis are listed as following:In the first part of this dissertation, in-situ synthesis of Hydrotalcite using calcined kaolin as the substrate has been investigated in details. The results show that the key point of synthesis is to optimize different factors such as reactant composition, crystallization time and crystallization temperature. The formation of hydromagnesite was observed at high concentration of Mg2+. High urea concentration resulted in the restoration of the calcined Kaolin to its raw structure and the formation of hydro-magnesite. Crystallization temperature plays an important role in synthesis, where massive hydromagnesite would generate at high temperature. In order to avoid the formation of hydromagnesite and enhance the crystallinity of hydrotalcite, alumina cake (Shandong) and aluminum nitrate were selected as additional aluminum sources. To our disappointment, all the hydrotalcite formed in the liquid phase after the addition of the additional aluminum sources. Besides, NH3-NH4NO3buffer system and hexamethylenetetramine were used instead of urea to regulate pH value of the system, respectively, however, no crystalline phase of hydrotalcite formed. This suggests that urea not only regulates the pH value of the system, but also intercalates into the kaolin and thus swells the layers, which is beneficial to the transformation of aluminum source in the calcined kaolin.The second part focuses on the preparation and modification of the hydrotalcite used as supports for gold nanoparticles. The catalytic activities of Au/MgAl-LDH decreased with the molar ratio of Mg/Al increasing. The activity increased greatly after the calcination-rehydration treatment to the supports. With the crystallinity of the hydrotalcites decreasing, the catalytic activity of Au/MgAlLDH increased gradually. Therefore, surface charge density, basic sites and surface defect centers of the supports have a major impact on the catalytic activities of Au/MgAlLDH. The last part of this dissertation is based on the previous studies. Generally, the number of surface defect centers increased with the particle size decreasing. Here, gold nanoparticles were deposited on matrix-based LDHs and used as the catalysts for alcohol oxidation. The nano-sized LDHs supported gold catalysts showed good catalytic activity, by using Kaolin-based LDH as the support. Furthermore, the active alumina-based LDH was used as the support for gold nanoparticles, showing excellent catalytic activity. The catalytic activity can be improved by increasing the load and crystallinity of LDH. Excellent supported gold catalyst was prepared by using alumina-based LDH as the support. This also provides a prospect approach to prepare industrial supported gold catalysts.