Adsorption and catalytic study of cyclopentyl methyl ether formation: structure-activity interplay in medium-pore zeolites

Abstract

Symmetrical and asymmetrical ethers produced from renewable feedstock play a key role in numerous green chemistry technologies. The aim of our contribution is to understand how textural properties and the location of active sites affect the mechanism of cross-etherification of cyclopentanol with methanol, which yields the asymmetric product cyclopentyl methyl ether. For this purpose, commercial MFI, nanosponge MFI, and nanolayered MFI zeolites with similar concentrations of acid sites, as well as medium-pore TUN and IMF zeolites with internal voids, slightly larger than those of MFI, were investigated by combining catalytic tests with infrared adsorption studies. Detailed FTIR analysis revealed three adsorption adducts, whose fractions varied with the alcohol loading and with the type of zeolite: i) a neutral single H-bonded adduct, ii) a bulky ionic H-bonded adduct, and iii) a neutral cyclopentoxy group. MFI zeolite is the most efficient catalyst in cyclopentanol cross-etherification, reaching 70% cyclopentyl methyl ether yield. Both hierarchical (48%-42%) and medium-pore (48%-58%) zeolites exhibited significantly reduced cyclopentyl methyl ether yields due to their larger internal voids and high number of strong Lewis acid sites, which presumably catalyze the undesired reaction of cyclopentanol dehydration to cyclopentene.