鎢鋯金屬氧化物摻混氧化铌用於甘油氣相脫水反應

生質柴油的製備是以動植物性油脂或回收食用油為原料，與短碳鏈醇（一般是甲醇）在觸媒的催化下進行轉酯化反應所得到的單鏈酯類。雖然生質柴油被視為極具發展潛力的替代性能源且各國生質柴油的生產力也逐年增加，但近年來生質柴油產量的增加速率並不如預期，其原因可能是無法有效降低生質柴油的生產成本。由於轉酯化反應大約會產生10 wt% 的甘油，因此若可以利用甘油生產其他具有經濟價值的化學品便可降低生質柴油的生產成本。在以甘油為起始物的眾多反應中以甘油氣相脫水生成丙烯醛最具有經濟價值。鎢鋯氧化物在甘油脫水生成丙烯醛反應中具有很高的活性，但是會因反應中產生的積碳而快速失活，因此本研究希望藉由摻混氧化铌來減緩觸媒的失活現象。根據氨氣程溫脫附技術的量測結果可知摻混氧化铌的鎢鋯氧化物觸媒屬於中弱酸的酸性。另外，根據二氧化碳程溫脫附技術的量測結果可知摻混氧化铌可以有效地降低觸媒表面的鹼含量，推測可能是因為氧化铌覆蓋二氧化鋯載體上的鹼性位子，而減緩觸媒的失活現象。實驗結果以氧化铌的重量比為氧化鎢加上氧化鋯重量的3% 並在450oC下煆燒的觸媒 (3–NbWOx/ZrO2–450) 具有最佳的催化活性表現。在反應第二十四小時甘油轉化率為81%，丙烯醛選擇率可以維持在70% 左右，且3–NbWOx/ZrO2–450觸媒可以藉由煆燒有效地恢復觸媒活性。

關鍵字

氧化鎢；二氧化鋯；鈮；甘油；丙烯醛

並列摘要

Biodiesels are fatty acid alkyl esters synthesized by transesterification of triglycerides with excess amounts of short chain alcohols, such as methanol, ethanol and propanol. The increasing production of biodiesels has resulted in over production of glycerol. The cost of biodiesels will be lowered down if glycerol can be used as a feedstock to produce high valued chemicals. Among different processes, the gas-phase dehydration of glycerol to form acrolein is considered to have great economical value. Tungstated zirconia has been found to be efficient catalysts for dehydration of glycerol to form acrolein. However, severe catalyst deactivation over tungstated zirconia was observed due to coke deposition. The aim of this study is to modify the WO3/ZrO2 catalysts by doping small amounts of Nb to decrease the catalytic decay. The acidic strengths of the catalysts measured by NH3-TPD were in the range of weak to moderate. The results of CO2-TPD measurements indicated the doping WO3/ZrO2 with small amounts of Nb can reduce the basic amount by coverd the basic sites of ZrO2 and further increase the stability. The optimal glycerol conversion of 81% and acrolein selectivity of 70% were obtained after 24 h time-on-stream over NbWOx/ZrO2 catalyst with Nb2O5/(WO3 + ZrO2) weight ratios of 3%. The spent catalysts could be easily regenerate by calcination and the catalytic activities were well retained.

並列關鍵字

WO3 ； ZrO2 ； Nb ； Glycerol ； Acrolein

參考文獻

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國際替代計量

鎢鋯金屬氧化物摻混氧化铌用於甘油氣相脫水反應

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