扁平狀SBA-15負載之鎢鋯鈮混合金屬氧化物觸媒用於氣相甘油脫水反應

生質柴油可以藉由動物性、植物性或是回收油脂作為原料，與短碳鏈的醇類(多為甲醇)在觸媒催化下進行轉酯化反應，而得到單鏈的酯類(生質柴油)與副產物甘油，而若是可以將副產物甘油有效利用，便可以降低生質柴油在製造上的成本，使其更具經濟競爭性。固態酸在催化劑的角色上具有易於控制酸性、熱穩定性高、易於再生重複使用等優點；鎢鋯鈮混合金屬氧化物在甘油脫水的反應中具有很好的丙烯醛選擇率，但是會因為反應過程中產生積碳覆蓋掉活性位置，而使得觸媒失去活性。在本研究中利用超臨界流體處理技術將混合金屬氧化物負載於不同的載體上(SBA-15-p, Al2O3, and MgO)，且改變混合金屬氧化物的負載方式與比例，進而增加觸媒的使用時間與提高丙烯醛的選擇率。同時，利用許多不同的鑑定技術(XRD, TPD, IR, SEM, TGA)來探討不同因素所造成的影響。結果發現具有較強的酸性的觸媒如：Nb10W40Zr50-SBA-15-p-H2O2、Nb11W30Zr59-Al2O3-H2O2會有較高的丙烯醛選擇率，但是同時較高的酸性也會使丙烯醛進行聚合反應而積碳失去活性；而負載在扁平狀SBA-15之鎢鋯鈮混合金屬氧化物的催化活性優於負載在酸性的Al2O3或鹼性的MgO。而且，金屬氧化物填入孔洞內的觸媒會比單單覆蓋在SBA-15表面的觸媒有較長的壽命。加入過多的氧化鈮雖然可以增加觸媒使用時間，但同時也會使丙烯醛選擇率降低，最後在兩項因素的權衡之下，會得到一組具有能較長使用時間(24小時後仍有70%以上得甘油轉化率)與較佳的丙烯醛選擇率(約為70%)的觸媒Nb11W30Zr59-SBA-15-p-H2O2。該組觸媒在重複使用上，具有方便再生(僅需加熱)與催化表現較佳(24小時後仍有70%以上得甘油轉化率、丙烯醛選擇率約為70%)的特點。

關鍵字

氧化鎢；氧化鋯；氧化鈮； SBA-15-p ；超臨界流體；甘油；丙烯醛

並列摘要

Solid acids have been found to be efficient catalysts for dehydration of glycerol to form acrolein. In this study, we chose mixed metal oxides to be the catalysts, because the acid strength is easy to control, they have good thermal stability, and they can be regenerated easily. In this study, mixed metal oxides containing Nb, W, and Zr were supported over various materials (SBA-15, Al2O3, and MgO) by impregnation method through super-critical-fluid treatment. The physico-chemical properties were characterized by several techniques, including NH3-TPD, XRD, and N2 sorption. The acidic support material (Al2O3) was found to give highest glycerol conversion and acrolein selectivity. However, the catalyst decayed rapidly. On the other hand, the catalysts prepared by one-step impregnation over platelet SBA-15 were found to be more efficient than others in maintaining the catalyst lifetime. Moreover, the catalyst with metal oxides entering the channels of SBA-15 (Nb11W30Zr59-SBA-15-p-H2O2), gave better catalytic activity than that just covered the outer surfaces (Nb11W30Zr59-SBA-15-t-H2O2). The most efficient catalyst could retain glycerol conversion of 69% and acrolein selectivity of 70% after 24 h time-on-stream.

並列關鍵字

WO3 ； ZrO2 ； Nb2O5 ； SBA-15 ； super-critical-fluid ； glycerol ； acrolein

參考文獻

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3. Katryniok, B.; Paul, S.; Bellière-Baca, V.; Rey, P.; Dumeignil, F., Glycerol dehydration to acrolein in the context of new uses of glycerol. Green Chemistry 2010, 12 (12), 2079.

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扁平狀SBA-15負載之鎢鋯鈮混合金屬氧化物觸媒用於氣相甘油脫水反應

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