Comparison of gas-phase dehydration of propane polyols over solid acid–base catalysts

• Reactions of glycerol, 1,2- and 1,3-propanediol on various acid–base catalysts were compared.
• Similarity between the dehydration reactions of 1,2-propanediol and glycerol were disclosed.
• 1,3-Propanediol reacted quite differently from 1,2-propanediol, as well as glycerol.
• Mechanistic consideration on the activation of propane polyols on acid–base catalysts is given.

Gas-phase dehydration of aqueous propane polyols including glycerol, 1,2- and 1,3-propanediols was investigated over various solid catalysts with a wide range of acid–base properties. Fairly high selectivity (40–75 mol%) for propanal formation from 1,2-propanediol, and acrolein from glycerol was obtained over the catalysts with high fractional acidity in the range of −8.2 < H0 ≤ −3.0, in which Brønsted acidity appeared advantageous over Lewis acidity. The dehydration of 1,3-propanediol produced quite scattered products and a clear relationship between its product selectivity and the catalyst acidity could not be established. Mechanistic implications of these observations are discussed, which point to that the dehydration reactions of both 1,2-propanediol and glycerol are initiated by activation of the hydroxyl group bonded with the central carbon atoms.

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