Catalytic dehydration of glycerol to acrolein over aluminum phosphate catalysts

Gas phase conversion of glycerol to acrolein over a variety of aluminum phosphate (AlP) catalysts synthesized by a simple replacement reaction method with a variation in calcination temperature (300-700 °C, AlP-300, AlP-400, AlP-500, AlP-600, and AlP-700, respectively) has been investigated. The textural properties, acidities and coke contents of the samples were also determined. The catalysts were presented in an amorphous state when the AlP sample was calcined below 500 °C. Further increasing the calcination temperature promoted the formation of orthorhombic α-AlPO₄ crystal. The weak acid sites increased when the calcination temperature was raised from 300 to 500 °C. However, the weak acid sites decreased when the AlP was calcined above 500 °C. The acidity of the catalyst played a crucial role in the glycerol dehydration reaction. The maximum acrolein selectivity of 66% at 98% glycerol conversion was obtained over AlP-500 catalyst, due to the largest number of acid sites and appropriate textural properties. AlP-700 exhibited the lowest glycerol conversion, owing to the formation of orthorhombic α-AlPO₄ crystalline phase and the lowest amount of acid sites under high calcination temperature. The significant reduction in the acidity of the used sample led to a decrease of glycerol conversion. (author)