SBA-15負載釩鉬鎢混合金屬氧化物對氣相甘油脫水氧化反應研究

Abstract

甘油脫水氧化形成丙烯酸的反應在工業上具有高度經濟價值，本研究欲探討同時具有酸性及氧化力的觸媒，以一步反應將甘油脫水氧化形成丙烯酸。此催化過程包含兩個連續的反應，先利用觸媒的酸性將甘油脫水形成丙烯醛，丙烯醛緊接著氧化形成丙烯酸。本研究利用不同比例之V/Mo/W金屬氧化物及將其負載於SBA-15上，觀察對催化所造成的影響，同時利用XRD、NH3-TPD、SEM 和 N2 吸脫附技術來探討不同因素所造成的影響。 催化條件測試中發現，當溫度為300oC、N2/O2/glycerol = 71/4.5/1、總體流速為50 mL/min及甘油進樣速率為3 mL/h時，擁有最佳的催化條件，將V/Mo/W金屬氧化物負載於SBA-15上會增加丙烯醛及丙烯酸的選擇率，同時降低氣體CO及CO2的選擇率。已知V對於丙烯醛氧化反應是有幫助的，然而，當V/W比例增加時，會使過度氧化的產物COx增加，而當V/Mo比例增加時，COx選擇率反而下降。在調整金屬比例V/Mo/W = 1/0/4後負載於SBA-15上，觸媒30%W4V1-SBA-15可得到最高的丙烯酸選擇率15%。

The catalytic behaviors of bifunctional catalysts with acidic and oxidizing properties were investigated in the one-step oxidehydration of glycerol to acrylic acid. The demonstrated reaction involves two consecutive steps of acid-catalysed glycerol dehydration into acrolein and aldehyde oxidation into acrylic acid. The aim of this study is to optimize the components of V/Mo/W mixed oxides and to examine the effect of supporting V/Mo/W over platelet SBA-15. The catalysts were characterized by XRD, NH3-TPD, SEM and N2 sorption techniques. The optimal reaction condition was 300oC, N2/O2/glycerol = 71/4.5/1, N2 flow rate of 50 mL/min, glycerol flow rate 3 mL/h. Supporting V/Mo/W mixed oxides on SBA-15 would enhance the yields of acrolein and acrylic acid and decrease the COx yields at the same time. On the other hand, V are active in oxidation reaction. However, the yields of over-oxidized COx products increased when the V/W ratio increased. On the contrary, the COx yield decreased when the V/Mo ratio increased. As a result, the highest yield of acrylic acid was obtained over the SBA-15 supported catalyst with V/Mo/W atomic ratio of 1/0/4. The highest acrylic acid selectivity of 15% was obtained over 30%W4V1-SBA-15 catalyst.