Gas phase dehydration of glycerol to acrolein over NaHSO₄@Zr‐MCM‐41 catalyst

Abstract

The NaHSO 4 @Zr-MCM-41 catalyst modified by dodecyltrimethoxysilane (DTMS) showed excellent performance during the dehydration of glycerol to acrolein. The glycerol conversion and acrolein selectivity and yield on NaHSO 4 -DTMS@Zr-MCM-41 (Cat-2) are higher than that of NaHSO 4 @Zr-MCM-41 (Cat-1). The dispersity of NaHSO 4 is remarkably improved by an appropriate amount of DTMS modification on Cat-2 because of the steric effect between DTMS and NaHSO 4 . Therefore, the total acidic amount of Cat-2 is more than that of Cat-1, but its acidic intensity is weaker than that of Cat-1. The more total amount of acidity is beneficial to improve the glycerol conversion, and weaker acid strength leads to less carbon deposition. The amount of Brønsted acid sites is more than that of Cat-1; however, the amount of Lewis acid sites is less, so the B/(B þ L) of Cat-2 is higher, which is beneficial and improves the acrolein selectivity. The Cat-2 catalyst has proper hydrophobicity by grafting the silane group on the support surface, which can suppress the leaching of NaHSO 4 because the water that existed in the glycerol aqueous solution and that was produced in the reaction is not easily adsorbed on the catalyst surface. The appropriate hydrophobicity is beneficial to the quick desorption of products, which can also suppress the coke formation. The stability of Cat-2 is obviously higher than that of Cat-1 because the coke that was deposited and the S elemental leaching on Cat-1 are more serious than that of Cat-2. The reaction pathway of the dehydration of glycerol was proposed, and the reaction conditions were optimized on the Cat-2 catalyst.