介孔洞SBA-15負載之鎢鋯氧化物用於氣相甘油脫水反應

Abstract

鎢鋯氧化物當作觸媒在許多酸催化反應中表現出色。甘油脫水形成丙烯醛的反應在工業上具有高度經濟價值，而介孔洞材料SBA-15具有高表面積，以及均勻六方角柱規則孔洞，加上良好的水熱穩定性，使其成為具潛力的觸媒載體。本研究使用超臨界乙醇將鎢鋯金屬前驅物帶入SBA-15材料孔洞中，接著煆燒處理，使其形成金屬氧化物，藉此增加觸媒表面積及金屬氧化物顆粒分散性，此外並使用不含載體的觸媒，和使用含浸法負載之觸媒來做比較。從X光繞射、氮氣吸脫附和電子顯微鏡實驗得知，利用超臨界乙醇法製成的鎢鋯氧化物複合材料保有原本SBA-15的規則六角柱狀排列。相較於直接含浸法，複合材料具有較高表面積以及保有介孔洞。實驗中改變不同的初始含浸溶劑、不同的SBA-15載體型態、不同煆燒溫度，以及鎢和鋯的負載順序，藉此觀察樣品在催化活性上的差異。 觸媒活性測試中，氣相甘油脫水反應在固定床反應器進行，將產物以氣相層析儀進行分析。實驗結果得知，對所有觸媒丙烯醛 (acrolein) 皆為主要產物，選擇率約80%，伴隨甘油一次脫水的副產物丙酮醇(hydroxyacetone)和其他副產物。使用扁狀SBA-15做為載體，和甲醇/水 (1:2, v/v)做為初始含浸溶劑的觸媒，有最好的甘油轉化率，且觸媒煆燒再生後，活性維持不變。煆燒溫度最佳化實驗中，以775 oC煆燒之樣品活性最佳，失活速率最慢。

Tungstated zirconia has been found to be efficient catalysts in many acid-catalyzed reactions. The gas-phase dehydration of glycerol to acrolein is of great economical value. Mesoporous SBA-15 has great potential as catalyst support due to its ordered pore structure, high surface area and good hydrothermal stability. In the present study, mesoporous SBA-15 was used as the support for preparing supported tungstated zirconia (WZ) catalysts in order to increase the surface area and the dispersion of metal oxides. The catalysts prepared through pre-impregnation and subsequent supercritical treatment were found to retain ordered porous structure and well-dispersed W/Zr catalytic sites based on the results of XRD, N2 physisorption and EM photos. Factors of catalyst preparation such as the pre-impregnation solvents, supporting sequences of active phases, and morphology differences of silica supports in influencing the catalytic performances were examined. The gas-phase dehydration of glycerol in the presence of water was investigated using fixed-bed reactor, and product analysis was performed by gas chromatography. From the catalytic results, all samples facilitated the same acrolein selectivity around 80%, with hydroxyacetone as the major by-product. The combination of platelet SBA-15 as support and MeOH/H2O (1:1 v:v) as pre-impregnation solvent gave catalysts having higher glycerol conversion. Moreover, the catalytic activities were retained after several cycles. The optimal calcination temperature for preparing the catalysts of the lowest deactivation rate was at 775 oC.