Conversion of glycerol into allyl alcohol over potassium-supported zirconia–iron oxide catalyst

• Catalytic conversion of glycerol was performed with iron oxide-based catalysts.
• Useful chemicals including allyl alcohol were produced from glycerol.
• Alkali metal-supported ZrO2–FeOX was effective in increasing allyl alcohol yield.
• K/Al2O3–ZrO2–FeOX showed higher structure stability and high allyl alcohol yield.
• K/Al2O3–ZrO2–FeOX was also applicable to the conversion of crude glycerol.

The catalytic conversion of glycerol was performed with iron oxide-based catalysts for production of allyl alcohol using a fixed-bed flow reactor at 623 K under atmospheric pressure. The glycerol dehydration proceeds on acid sites of catalysts while the allyl alcohol production is assumed to be catalyzed by non-acidic sites of catalysts through a hydrogen transfer mechanism. Different alkali metals, including Na, K, Rb, and Cs were supported on ZrO2–FeOX and all of them gave impressively higher allyl alcohol yield and suppressed glycerol dehydration due to the reduced catalyst acidic property. K-supported ZrO2–FeOX (K/ZrO2–FeOX) was chosen for further studies, and allyl alcohol yield remarkably increased up to 27 mol% C at the K content of 3–5 mol%. Since no external hydrogen gas is supplied to the system, the hydrogen transfer mechanism should take place between the reaction of glycerol and either hydrogen atoms derived from formic acid forming during the reaction, or active hydrogen species produced from the decomposition of H2O by ZrO2.Addition of Al2O3 to K/ZrO2–FeOX (K/Al2O3–ZrO2–FeOX) was examined in order to improve structure stability during the glycerol conversion. Al2O3 addition to the catalyst was effective to achieve higher structure stability, leading to high glycerol conversion with stable allyl alcohol yield of above 25 mol% C. Moreover, K/Al2O3–ZrO2–FeOX can be applicable to the conversion of crude glycerol which is the waste solution obtained from biodiesel production.

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