含金屬並具有微晶型孔壁SBA-1的合成、鑑定及催化活性之探討

Abstract

本研究在鹼性的環境下 (pH~9) 合成結晶型孔壁之含鋁SBA-1介孔材料，模板使用cetyltriethylammonium bromide (CTEABr)，而矽源是用含鋁的ZSM-5 seeds，合成出來的介孔材料稱為Al-ZSBA-1，其鋁含量可以高達5.7%並擁有規則性排列之3D cubic Pm3n的結構、高表面積 (600 m2/g) 和孔洞體積，經由NH3-TPD和離子交換法可測量出Al-ZSBA-1的酸性性質，從27Al MAS NMR知道大部分的Al都是四配位，我們也合成出非晶型孔壁之含鋁SBA-1 (Al-SBA-1-alk)，並比較這兩種觸媒的催化活性，使用的催化反應為2,4-di-tert-butylphenol (DTBP) 和cinnamyl alcohol經由Friedel-Crafts reaction產生中間產物2,4-di-tert-butyl-6-cinnamylphenol (DTBCP)，再經由Michael addition可得到最終產物為flavan，由催化結果得知擁有結晶型孔壁之介孔材料的酸性強度會比較高，flavan選擇率會跟ZSM-5相似，其中以7Al-ZSBA-1的催化效果最好，flavan的選擇率和產率分別為75%和39%。 另外，我們也在鹼性的環境下成功地合成具有三維孔洞結構的含鈦介孔材料 (Ti-SBA-1-alk)，接著使用沉積沉澱法將金離子放在含鈦介孔材料，命名為yAu3+/xTi，所得材料經由XRD、N2 adsorption-desorption isotherms、UV-Vis spectra、ICP-MS和TEM等技術鑑定，可得知所合成出來的材料擁有很好的三維介孔結構、表面積可達到800 m2/g以上以及很高的孔洞體積，而且當Ti/Si莫耳比小於3%時，大多數的鈦離子是在骨架中的四面體中心，並且由TEM和ICP-MS得知金奈米粒子的大小與金含量是成正相關的，而金含量會隨著鈦含量提高而提高。 藉著改變金和鈦的含量，探討金和鈦之間的協同效應對催化丙烯環氧化反應的活性，發現當金含量小於1wt%時，會得到很高的PO選擇率，其中以10Au3+/3Ti觸媒的催化效果最好，丙烯的轉化率和環氧丙烷的選擇率分別可達到7.4%和91.7%，其氫氣的選擇率高達38.3%。我們也使用TS-1 seed當作矽源成功地合成出具有結晶型孔壁含鈦的介孔材料，命名為Ti-ZSBA-1，其物理與化學性質都跟Ti-SBA-1-alk很相似，然而，其催化活性會比Ti-SBA-1-alk高，最重要的是觸媒的失活現象有所改善，其中以10Au3+/3TiZ觸媒的催化表現最好，丙烯的轉化率和環氧丙烷的選擇率分別可達到8.64%和92.6%，其氫氣的選擇率高達43.5%。

Cubic Pm3n mesoporous aluminosilicate isomorphous to SBA-1 with three-dimensional inter-connected pore structures was prepared in alkaline condition (pH around 9) using aluminum-incorporated ZSM-5 seeds as the Si and Al sources and cetyltriethylammonium bromide (CTEABr) as pore-directing agent with the aid of NaCl salt. The resultant materials (termed Al-ZSBA-1) with Al loading up to Al/Si molar ratio of 0.057 have cubic Pm3n structure and high surface areas (ca. 600 m2/g). They showed stronger acidities than the counter materials prepared using sodium silicate as the silica source (referred as Al-SBA-1-alk). Moreover, all the Al in Al-ZSBA-1 retained in tetrahedral coordination after calcination at 823 K, while a portion of Al incorporated in Al-SBA-1-alk became octahedrally coordinated. When applying the materials as catalysts in the alkylation of 2,4-di-tert-butylphenol (DTBP) with cinnamylalcohol to form flavan, Al-ZSBA-1 gave higher flavan selectivity of 75% and yield of 39% than Al-SBA-1-alk, mordenite, ZSM-5, and beta zeolites. These results demonstrated that the Al-ZSBA-1 materials owned the advantages of strong acidity from zeolite nanostructures and good diffusivity from mesopores. In addition, cubic Pm3n mesoporous Ti-incorporated silica with 1-5mol% Ti content have been prepared by co-condensation method and gold clusters were deposited on these supports by deposition-precipitation (DP) method. These resultant materials (termed yAu3+/xTi, x and y represent the Ti/Si molar percentage and Au/support weight percentage in the synthesis solution, respectively.) were characterized by XRD patterns, N2 adsorption-desorption isotherms, UV-Vis spectra and TEM. All samples have cubic Pm3n structure and high surface areas. The studies by UV-Vis spectra indicated that the Ti(IV) in the catalysts with low Ti content was favorably in tetrahedral (Td) coordination, whereas for the catalysts with Ti/Si molar ratio above 5%, a larger amount of Ti(IV) was in octahedral coordination. TEM images showed that the average particle size is larger than 3 nm as actual gold loadings is above 1wt%. The catalytic results showed the catalyst with low actual gold loadings (< 1wt%) which is more selective to PO, while at high gold loadings (> 1wt%), the catalyst showed lower PO selectivity. In propylene epoxidation with H2 and O2, 7.4% propene conversion and > 90% PO selectivity were achieved over 10Au3+/3Ti catalyst. We also successfully synthesized Ti-ZSBA-1 materials with zeolitic wall by using TS-1seeds as silica source and CTEABr as surfactant. The 10Au3+/3TiZ catalyst gave higher propylene conversion of 8.6% and PO selectivity of 92.6% than 10Au3+/3Ti. Most of all, the deactivation problem was improved significantly and the decay rate of 10Au3+/3TiZ is smaller than 10Au3+/3Ti.