| Acid catalysts play a vital role in the economic development of the chemical industry. Many organic reactions, for example, alkylation, unsaturated hydrocarbon isomerization, esterification, cracking, condensation and so on are accomplished by acid catalysts. Since1940s, solid acids have been widely investigated to reduce the impact on the environment and to decrease costs.Among all kinds of heterogeneous acid catalysts, zeolite such as HZSM-5, beta zeolite and zeolite Y which have strong acidity and large amount of active sites have been extensively applied in industrial acid catalysis since the last century. However, their microporous structure has restricted their applications in large molecule acid reaction. In the early1990s, the meso-structured silicates firstly reported opens the new application field for the heterogeneous acid catalytic system for large molecular substrates. Binary mixtures of metallic oxides were applied in acid catalysis.In this dissertation, we synthesized a series of mixed metal oxides, adjusted the acidity of these catalysts and applied them into Friedel-Crafts (F-C) reaction.In chapter3, ordered mesoporous aluminum silicates with strong acid sites were synthesized by sol-gel method. The amount of surfactant and the Si/Al mole ratio would both affect the materials’meso-structure; while, the amount of HAc has little effect on the structure. The Si/Al mole ratio played an important role in catalytic activity and the aluminum silicates with Si/Al=10showed the best acid catalytic activity. NH3-TPD and Py-FT-IR suggested that the aluminum silicates with Si/Al=10had much more Bronsted acidic sites than that of other Si/Al ratios.In chapter4, we have successfully synthesized mesoporous titania-silica materials with moderate strong Bronsted acid sites via a sol-gel with nonionic surfactants precursors. The Ti/Si mole ratio plays a very important role in determining the acidic property of materials, only six-coordinated Ti species can generate Bronsted acid sites. The number of the Bronsted acidic sites can be increased via a high-temperature hydrogenation process, which subsequently improves their catalytic performance in the F-C reaction of anisole and benzyl alcohol. Furthermore, TEOS partly submitted by PTMS as the silica precursor can increase the activity of materials.In chapter5, we synthesized mesoporous zirconia-tungsten oxide via a sol-gel process with nonionic surfactants precursors. We identified that the subnanometer WOx clusters act as the most active sites for the F-C reaction. Most importantly, we show that the formation of these subnanometer WOx clusters can be rationally controlled by adjusting W concentration and calcination temperatures, which is of great importance in the design of solid acid catalyst. It is shown that a minimum W concentration (0.07at the calcination temperature of800℃) and a minimum calcination temperature (650℃at a given W concentration of0.1) are required during the preparation of these acid catalysts for the development of highly active subnano WOx clusters.In chapter6, mesoporous ZrO2-WO3materials with strong acid sites were successfully synthesized by low temperature calcination that is far below the threshold temperature to develop strong acidity. The formation of these strong acid sites can be well controlled by varying the type and concentration of the added surfactants, which is of great importance for the design of the solid acids with strong acid sites.In chapter7, The number of the Bronsted acidic sites of mesoporous ZrO2-WO3materials can be increased via calcined in Air after NH3calcination, which subsequently improves their catalytic performance in F-C reaction of anisole and benzyl alcohol. More important, the way to increase the acid sites via air calcinations after calcined in NH3provides a rational process to regulate their acid property and corresponding catalytic performance. |
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