石油在人們日常生活中需求量極高，但石油為非再生能源，且環保意識崛起，生質柴油越來越受重視。因在鹼性催化劑催化下反應速率較快，生質柴油一般使用鹼性催化劑透過轉酯化反應生成，但廢油中所含游離脂肪酸(FFA)較高，易與鹼性催化劑反應產生皂。因而在此步驟前之前先使用酸性催化劑，透過酯化反應將FFA含量降低後再使用鹼性催化劑，減緩皂化現象。
本實驗主旨為開發一低成本、對環境友善之酯化反應酸性催化劑，選擇使用δ-MnO2作為新的酸性催化劑，期望藉由層狀結構的δ-MnO2摻雜不同過渡態金屬陽離子，提升δ-MnO2作為固態酸性催化劑之活性。XRD分析摻雜陽離子濃度對δ-MnO2晶面間距的改變，得到摻雜之飽和濃度比例，並以ICP-OES分析催化劑實際組成，除了鉻離子沒有摻雜到δ-MnO2 外，各元素摻雜之濃度為：Cu/Mn = 0.06、Fe/Mn = 0.07、Ni/Mn = 0.16、Co/Mn = 0.4，並以銅摻雜與未摻雜之催化劑代表，比較TEM結果差異，確認可以透過此實驗合成法將陽離子摻雜進錳氧化層中。
根據酯化反應結果，摻雜不同過渡態金屬陽離子可提高δ-MnO2作為酯化反應非均相酸性催化劑效能。以XPS、UV-Vis與UPS分析，發現摻雜過渡態金屬陽離子使δ-MnO2中Mn3+/Mn4+比例上升、FFA與催化劑間電子轉移能障減小，可能使摻雜的δ-MnO¬2成為活性較高的固態酸性催化劑。

Biodiesel is produced by transesterification and esterification with basic and acidic catalyst, respectively. This work modified δ-MnO2 with different transition metal cation dopants (Cu, Cr, Co, Ni and Fe) as acidic catalyst. Doping concentration was determined from d-spacing changes of XRD patterns (fine scan). According to ICP results, cations can dope into δ-MnO2 except Cr ions by calcination method. Comparing results between conversion of esterification and XPS, UV-Vis and UPS analysis, it showed that higher Mn¬3+/Mn4+ atomic ratio and reduced electron transfer barrier produced higher conversion. Fe-doped δ-MnO2 had the highest FFA conversion (85%) in comparison to other the catalysts under the same reaction conditions.

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