Role of the mesopore generation method in structure, activity and stability of MFI catalysts in glycerol acetylation

Abstract

The relative stability of microporous and hierarchical ZSM-5 zeolites in the acetylation of glycerol with acetic acid in liquid phase batch reactions is investigated. Microporous ZSM-5 is synthesized via a hydrothermal synthesis route. A hierarchical pore structure in the ZSM-5 is created by two techniques, (i) alkaline desilication of the microporous ZSM-5 (top-down synthesis), and (ii) hydrothermal synthesis using a mesoporogen organosilane surfactant as the structure-directing agent (bottom-up synthesis). The chemical and structural properties of the fresh and spent catalyst are studied and compared by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, pyridine adsorption followed by Fourier transform infrared spectroscopy (Py-IR), scanning electron microscopy (SEM) and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and 29Si MAS NMR spectroscopy. The highest conversion of glycerol (99%) was obtained with the hierarchical zeolite obtained via bottom-up synthesis; however this catalyst failed to provide high reactivity in recycle runs. In contrast, consistent reactivity is obtained over the desilicated zeolites in recycle runs. Characterization of the spent catalysts demonstrates that the desilicated zeolite samples maintain key physical properties and therefore, performed well in the acetylation of glycerol with acetic acid.