嫁接法製備含鈦 MWW 沸石的研究、材料鑑定及催化 活性之探討

Preparation of Ti-incorporated MWW zeolites by grafting method, material characterization and catalytic performance studies

張志成(Chih-Cheng Chang)

指導教授 ： 鄭淑芬

國立臺灣大學/理學院/化學研究所/博士(2017年)

https://doi.org/10.6342/NTU201700834

摘要

本文以嫁接方式製備含鈦於MWW層狀結構之孔洞材料，包括MCM-22與ERB-1兩種同樣具MWW結構之微孔沸石以及利用氧化矽支撐ERB-1而得同時具微孔與介孔之MCM-36二氧化矽，並針對使用不同鈦前驅物作為嫁接試劑及不同溶劑的影響進行探討。利用XRD、N2 adsorption-desorption isotherms證實嫁接法製備之Ti-MCM-22的MWW層狀結構完整。ICP-MS檢測Ti-MCM-22的鈦量，於合成溶液矽鈦比等同條件下，鈦含量隨著選用體積較小的鈦前驅物可以引入更多Ti(IV) 於MCM-22上，不同鈦前驅物所製備而得的Ti-MCM-22含鈦量的關係為Ti(O-Et)4 > Ti(O-Pr)4 > Ti(O-Bu)4。UV–Vis 與XANES光譜證實有四配位與六配位鈦存在於Ti-MCM-22，其中六配位鈦的訊號隨著合成時的鈦源使用量減少而降低。選用嫁接溶劑對於Ti(O-Et)4製備Ti-MCM-22，UV–Vis 檢測Ti-MCM-22以2 M HNO3水溶液移除骨架外TiO2，1-butanol相較於ethanol更能夠維持鈦活性。29Si NMR光譜揭露Ti-MCM-22樣品中大部分的Ti(IV)可能處在supercage底部。應用Ti-MCM-22催化環己烯與環辛烯的環氧化反應，以t-butylhydrogen peroxide作為氧化劑，發現選用Ti(O-Et)4 作為嫁接劑所製備的Ti-MCM-22具有最佳催化結果，優於Ti-YNU-1或以Ti(O-Pr)4及Ti(O-Bu)4作為嫁接劑所製備的Ti-MCM-22觸媒。
以ERB-1為起始物合成具有微孔與介孔之MCM-36。再利用嫁接法製備Ti-MCM-36觸媒。探討使用Ti(O-Et)4、Ti(O-Pr)4及Ti(O-Bu)4三種鈦嫁接試劑及不同溶劑(1-butanol、ethanol及toluene)的影響。利用XRD、N2 adsorption-desorption isotherms佐證Ti-MCM-36的MWW結構完整。ICP-MS檢測Ti-MCM-36之鈦含量隨著鈦嫁接試劑的體積減小而增加，得到Ti-MCM-36樣品之Si/Ti比值有 Ti(OEt)4 < Ti(OiPr)4 < Ti(OBu)4 的趨勢。由UV–vis 與XANES光譜可觀察Ti(IV)的配位環境，發現以ethanol及toluene為溶劑所進行的嫁接反應所得Ti-MCM-36會有較多TiO2 團簇甚至顆粒生成。在環己烯、環辛烯與雙環戊二烯的環氧化反應裡，使用Ti(O-Et)4為嫁接劑所製備之Ti-MCM-36觸媒顯示良好的催化表現，優於Ti-YNU-1與Ti(O-Pr)4及Ti(O-Bu)4作為嫁接劑製備的Ti-MCM-36觸媒。當TBHP/DCPD=3.5，雙環戊二烯獲得接近100%轉化率及95% diepoxide選擇率

關鍵字

MCM-36 ； 嫁接 ； 介孔 ； 還氧化

並列摘要

Ti(IV) incorporated layered stacking MWW zeolites with containing similar porous structure of ERB-1 and MCM-22 precursors (Ti-MCM-22 and Ti-ERB-1) and ERB-1 precursor as starting material subsequently further prepared micro-/mesoporous silica MCM-36 by silicates pillars (Ti-MCM-36) through a simple grafting method using different titanium alkoxides, including Ti(OEt)4, Ti(OiPr)4 and Ti(OBu)4 onto the post-treated calcined MWW. The X-ray diffraction patterns and N2 sorption isotherms confirmed the retention of basal MWW layer structure in Ti-MCM-22. The Si/Ti molar ratios analyzed by ICP-MS increased with the size of titanium alkoxides and varied in the order of Ti(OEt)4 < Ti(OiPr)4 < Ti(OBu)4 based on the same amounts of titanium alkoxides used in the grafting solutions. The UV-Vis and X-ray absorption spectra revealed that both tetrahedrally and octahedrally coordinated Ti(IV) species were present on Ti-MCM-22 prepared by grafting. However, the amount of octahedral Ti(IV) decreased with the decrease in Ti content. After acidizing with 2 M HNO3 concentration on Ti-MCM-22 due to the purpose of removed extra-framework TiO2 species, UV-Vis observation presents that 1-butanol has a well-retained Ti-anchored activity rather than ethanol as grafting solvent. Solid state 29Si NMR spectra indicated that most Ti(IV) were incorporated near the T-sites on the open bottom of the supercage, which were easily accessed by grafting agent. When applied in epoxidation of cycloalkenes, Ti-MCM-22 prepared by grafting with Ti(OEt)4 demonstrated better catalytic activities than Ti-YNU-1 or those grafting with Ti(OiPr)4 and Ti(OBu)4. The best catalytic performances were obtained over Ti-MCM-22 with Si/Ti molar ratio of ca. 100 prepared by grafting with Ti(OEt)4. The conversions were very high and epoxide selectivities were close to 100% in cyclohexene and cyclooctane oxidation using t-butylhydrogen peroxide as the oxidant.
ERB-1 precursor as initial material follows the step-by-step experimental procedure to derive micro-/mesoporous silica MCM-36. Ti(IV)-incorporated MCM-36 (Ti-MCM-36) was prepared by a simple grafting method using different titanium alkoxides, including Ti(OEt)4, Ti(OiPr)4 and Ti(OBu)4 in various solvents, including ethanol, 1-butanol, and toluene. The X-ray diffraction patterns and N2 sorption isotherms confirmed the retention of the basal MWW layer structure in Ti-MCM-36. The Si/Ti molar ratios analyzed by ICP-MS increased with the size of titanium alkoxides and varied in the order of Ti(OEt)4 < Ti(OiPr)4 < Ti(OBu)4 based on the same amounts of titanium alkoxides used in the grafting solutions, while the solvent had little influence on the Ti loading. UV–vis and XANES spectra showed that titanium species were mainly tetrahedral coordinated Ti(IV) and small amount of titania clusters when grafting in ethanol and 1-butanol, while large bulky titania crystallites were formed in toluene. Ti-MCM-36 prepared by grafting with Ti(OEt)4 in 1-butanol demonstrated better catalytic activities in epoxidation of olefins, including cyclohexene, cyclooctene and dicyclopentadiene (DCPD) than Ti-YNU-1 or those grafted with Ti(OiPr)4 and Ti(OBu)4. In DCPD oxidation using t-butylhydrogen peroxide (TBHP) as the oxidant, about 100% DCPD conversionand 95% diepoxide selectivity could be achieved using TBHP/DCPD molar ratio of 3.5.

並列關鍵字

MCM-36 ； grafting ； mesoporous ； epoxidation

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