Hydrotalcite Modified Base-catalyzed Reaction

Heterogeneous basic catalysts are economically and ecologically important because they are non-corrosive, environmentally benign and present fewer disposal problems. Therefore, the development of solid basic catalysts has recently gained much attention. In this thesis, three types of heterogeneous basic catalysts, i.e. eggshell catalyst, reconstructed hydrotalcite and graphene oxide-Mg/Al LDHs composite were prepared. The catalysts were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), thermogravimetric analysis (TGA) and N2-physisorption. The catalytic performances of the prepared catalysts were tested in transesterification of propylene carbonate and methanol, and Aldol condensation of benzaldehyde and acetone. The main contents are shown below:Dimethyl carbonate is receiving more and more attention because it is an important methylating and carbonylating agent. In this thesis, eggshell catalysts, prepared from eggshell waste, were tested in the synthesis of dimethyl carbonate from propylene carbonate and methanol. The effects of calcination temperature on structure and activity of eggshell catalysts were investigated. The reusability of eggshell catalysts was also examined. It was found that highly active, reusable solid catalyst was obtained by just calcining eggshell. Dimethyl carbonate yield of75%can be achieved at25℃and1atm pressure. Utilization of eggshell as a catalyst for dimethyl carbonate production not only provides a cost-effective and environmental friendly way of recycling this solid eggshell waste, but also makes the process of dimethyl carbonate production economic and fully ecologically friendly.Rehydrated hydrotalcite is a highly active heterogeneous base catalyst for a wide variety of organic reactions. Conventional methods for preparing reconstructed hydrotacite are complex and time-consuming. Furthuremore, the rehydrated hydrotalcite by conventional methods is easily deactivated when it contacts with air. Here, we report a procedure to effectively prepare reconstructed hydrotalcites. Mg-Al mixed oxide, which is originated from hydrotalcite, is directly added into the aqueous-phase reaction system of Aldol condensation without protection of inert gas. Under the reaction condition, the reconstructed hydrotalcite is in-situ generated, and is used as catalyst of Aldol condensation as soon as it forms, resulting in elimination of the deactivation of reconstructed hydrotalcite. The experimental results show that the in-situ reconstructed hydrotalcite had higher catalytic activity than that by conventional method. We provide a simple and effective method for reconstructed hydrotalcite.Inorganic compound-graphene oxide composite has many new special properties, comparing with pure graphene oxide. The general method for its preparation is hydrothermal synthesis. This method is complicated and time-consuming. Furthermore, it involved one step of stripping the graphite oxide. We prepared a series of graphene oxide-Mg/Al LDHs composite by deposition-precipitation method. This method is simple. The formation mechanism of the composite was also studied. It was found that graphite oxide can be gradually stripped by changing the proportion of Mg/Al HT with grapheme oxide.