On the cover：Anatase TiO2 (101) facets catalyze the 2-propanol dehydration reaction with a faster turnover rate than its (001) facets because molecular 2-propanol dehydration dominates on TiO2 (101) while, on TiO2 (001), 2-propanol simultaneously converts to more stable 2-propoxide before dehydration, which then requires higher activation energies for water elimination.
Alkanol dehydration on Lewis acid–base pairs of transition metal oxide catalysts is a reaction of importance in oxygen removal from biomass-derived feedstocks and their conversion to chemicals in general. However, catalysts with a high degree of structural heterogeneity, such as commercial TiO2 powders, are not well-suited to establish rigorous structure–function relationships at an atomic level. Here, we provide compelling evidence for the effects of surface orientation of TiO2 catalyst on elimination reactions of alcohols. Two anatase titania model catalysts, with preferential exposure of (101) and (001) facets, were synthesized and studied for 2-propanol dehydration using kinetic, isotopic, microscopic, and spectroscopic measurements, coupled with DFT calculations. Surface Lewis acid sites were found to be active for 2-propanol dehydration, and (101) facets are more reactive than (001) facets under the reaction conditions studied. On both anatase surfaces, 2-propanol was found to dehydrate via concerted E2 elimination pathways, but with different initial states and thus also different intrinsic activation barriers. Molecular 2-propanol dehydration dominates on TiO2 (101) while on TiO2 (001), 2-propanol simultaneously converts to more stable 2-propoxide before dehydration, which then requires higher activation energies for E2 elimination.
過渡金屬氧化物催化劑上的烷醇脫水反應是生物質原料脫氧及其化學轉化的重要反應。然而，具有高度結構不均勻性的催化劑，如商業化的二氧化鈦粉末，並不適合在原子水平上建立嚴格的結構-功能關係。在這裡，我們為 TiO2催化劑表面取向對醇消除反應的影響提供了令人信服的證據。合成了兩種銳鈦礦型二氧化鈦模型催化劑，以(101)和(001)為優先曝光劑，採用動力學、同位素、顯微鏡和光譜測量等方法，結合密度泛函理論(DFT)計算，研究了該催化劑對異丙醇脫水反應的催化性能。在研究的反應條件下，表面路易斯酸中心對異丙醇脫水具有活性，(101)面比(001)面反應活性更強。在兩種銳鈦礦結構表面均發現2- 丙醇通過協同的 E2消除途徑脫水，但初始狀態不同，內在活化障礙也不同。在 TiO2(001)表面，分子2- 丙醇脫水可以使 TiO2(101)脫水，而在 TiO2(001)表面，2- 丙醇在脫水前可以同時轉化為較穩定的2- 丙氧基，這就需要較高的活化能來消除 E2。
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關鍵字: dehydration 催化 封面
