二甲苯是合成纖維、塑化劑、樹酯很重要的原料。因而利用價值較低的甲苯與三甲基苯轉化成二甲苯的反應就相當地重要。而沸石正是此類反應的觸媒。由於反應物具有苯環的結構，對於較小孔洞結構的ZSM-5沸石來講(10-membered ring)，反應物較難有效地擴散到孔洞內的活性位置上。此時較大孔洞的BEA沸石(12-membered ring)便有較高的應用價值。相較於微米級沸石，奈米沸石具有特高的外表面積與較短的擴散路徑，有利於某些特定觸媒反應或吸附程序。由文獻得知，要合成出小粒徑的BEA沸石就必須提升有機模板比例或將反應溫度降低，但這會導致反應時間拉長，而且離心後產率偏低。 在我們實驗室過去的研究中已知利用極低的水/氧化矽比例，可提高氧化矽過飽和狀態，進而增加成核速率而限制粒子成長。可快速合成出奈米silicalite-1 沸石結晶。為了彌補文獻中的不足，本研究延續過去的合成法，並參考文獻的配方與水熱溫度，試著合成出BEA 沸石。 在本研究中我們發現藉由改變前驅物成份比例，先移去水解所產生的醇類，再將多餘的水份移除。可得到高濃度的透明前驅溶膠。之後在90℃水熱增加溶膠中粒子聚集速度，使其慢慢成核並結晶。經由反應過程中每一步驟的儀器分析與鑑定，已掌握較佳的實驗條件，目前可穩定合成出小於50 nm的均一BEA沸石粒子，而且離心後的回收產率提高至60 wt%，大大地改善文獻中產率通常低於20 wt%的缺點。 Zeolite BEA, with large pore size of 12-membered ring pore openings, is an industrial important catalyst for the transalkylation of toluene and C9 aromatics to produce xylene. It is also expected that if beta zeolite is made into nanocrystals, the higher external surface area may reduce the diffusion length and make the catalyst more effective. Consequently, the synthesis of beta zeolite nanocrystals has been the objectives of many researches. To synthesize smaller zeolite nanoparticles, one can either increase the ratio of organic-template or reduce the hydrothermal temperature. However, the consequence is longer hydrothermal time and lower zeolite yield. Based on our experience in the synthesis of MFI zeolite, a pre-concentrating step before low temperature hydrothermal seemed to accelerate the formation of crystal nuclei and speed up the crystallization. The objective of this research is to applied the experience on MFI zeolite to beta zeolite system and verify if we can improve the zeolite yield without sacrifice the particle size. 1SiO2:0.04AIP:0.36 TEAOH:25H2O was found to be a better recipe. At first the EtOH was removed to force complete hydrolysis and the zeolite beta precursor would be concentrated to speed up the aggregation. Finally, the precursor was transferred to 90℃ for nucleation and crystallization. The formation of zeolite from precursor and its aggregation and growth was monitored to understand the kinetics, based on which the final zeolite particle size could be controlled. Finally, Beta zeolite nanoparticles with uniform particle size distribution (<50 nm ) are successfully prepared from zeolite precursor. The yield of centrifugation could be 60 wt%.
