The Synthesis Of Stable Mesoporous Solid Acid/Base And Their Catalytic Application

Owing to the high surface area as well as open and ordered mesoporous structure, the mesoporous solid acids or bases have been promising catalysts in industrial catalysis. However the main disadvantages of the current mesoporous solid acids are the lack of thermal and hydrothermal stability and weak active sites. Nonetheless, strong active sites and stability are required in the industrial processes. Therefore, it is extremely essential to fabricate the mesoporous solid acids with strong acidity and stability.In the Chapter 2, we first came up with a new concept, named as "mesoporous ceramic acid". The ceramic acid is a kind of solid acid, which is calcinated at the temperature more than 1000℃, and thus it has an excellent thermal stability. However, its surface area is fairly low and its acidic strength is inadequate because of the high calcination temperature, which limits its application. In this Chapter, the mesoporous tungstate zirconia ceramic acids were successfully synthesized via the combination of extra-large pores mesoporous silica (EP-FDU-12) with thick walls and the tungstate zirconia solid acid. Specifically, EP-FDU-12 was used as a hard template and the precursors of tungsten and zirconium were coated onto the internal surface of EP-FDU-12 in ethanol solution. The resulted mesoporous ceramic acid (EP-WZrOx-T) not only exhibits high thermal stability, but also strong acidity, porous network, high surface area and hydrothermal stability. In the Chapter, the Friedel-Crafts reaction of benzyl alcohol and anisole was used as a probe reaction. The conversion of benzyl alcohol reached 58% for EP-WZrOx-1000 in 2 h. In contrast, WZrOx solid acid prepared by traditional sol-gel method was totally inactive for the F-C reaction.In Chapter 3, we used another strategy, ammonia hydrothermal treatment, to enhance the stability of the tungstate zirconia solid acid. The tungstate zirconia was dissolved under hydrothermal conditions resulting in a tetragonal zirconia crystal, which was formed at a high loading of tungsten. The resulted tetragonal structure was formed due to high distribution of tungsten throughout the zirconia framework. These hydrothermal treated catalysts (WZrOx-N-800) were then employed in the F-C reaction for the conversion of benzyl alcohol. This resulted in an activity, which was two times higher than that for the untreated catalysts (WZrOx-800).As the mesoporous framework and hydrothermal treatment are the two factorsresponsible for the improved stability of the catalyst therefore, the two factors were combined. The ultra-stable catalysts that were mesoporous niobium oxide, iron oxide and zirconia were synthesized through loadings of the metal precursors within the surface of mesoporous silica. This enhanced stability was illustrated through mesoporous niobium oxide, which tended to show stability at a calcination temperature upto 600℃, which in comparison to pure niobium oxide which was calcined at 400℃.In the Chapter 4, the method of preparation was extended to get other series of mesoporous ceramic acid. At the beginning, elements like aluminum (Al) and zirconium (Zr) were introduced in to the mesoporous silica (EP-FDU-12) named as EP-AlSiOX-T and EP-ZrSiOx-T. However, AlSiOx-T and ZrSiOx-T were selected which were synthesized by traditional sol-gel method without EP-FDU-12, for comparison to the present catalyst (EP-AlSiOx-T and EP-ZrSiOx-T). These selected and the presently synthesized catalysts were tested via in the F-C reaction for the calcinations temperatures. It was found that, at 800℃, AlSiOx-T and ZrSiOx-T were totally inactive. However, in contrast, EP-AlSiOx-T and EP-ZrSiOx-T showed maximum conversion of benzyl alcohol that is 100%. Then, in order to further enhance the acidity of the current catalyst systems that is EP-AlSiOx-T and EP-ZrSiOX-T, elements W and Mo were introduced to them.It has been known that biomass, being large in size, possess high molecular mass. Therefore, the catalysts used in their biomass conversion should possess large pore size, water tolerance and higher hydrothermal stability. Incidentally, our mesoporous ceramic acid exhibits these properties. Therefore, they were used for biomass conversions. This was successfully implemented through our collaborators, Wang group from East China University of Science and Technology.In these conversions, mesoporous ceramic acids (EP-AlSiOx-T) were employed for a conversion of glucose to the HMF. This conversion resulted in higher selectivity of 70%, which was expected due to the strong acid sites.In the Chapter 5, the mesoporous solid base, Na2WO4-Mn/FDU was synthesized. The latter is a good catalyst for the oxidative coupling of methane. This catalyst (Na2WO4-Mn/FDU) was also synthesized through similar method with that of synthesizing mesoporous ceramic acid. In comparison to the reported Na2WO4-Mn/SiO2 catalyst has very low surface area (<10m2/g), the Na2WO4-Mn/FDU has higher surface area (50 m2/g). The catalytic activity of thesetwo catalysts was compared through oxidative coupling reaction and the Na2WO4-Mn/FDU resulted in an increase in the yield of ethylene by 5%.