The recent direction of the catalysis field has been towards increased catalyst selectivity. For porous materials, shape selectivity is one type of way to attain catalyst selectivity. Microporous materials like zeolites can incorporate shape selectivity properties by constraining which products can actually form in and leave their pores. Whereas shape selectivity has permeated Bronsted acid zeolites, less is known about Lewis acid zeolites. One such group of reactions where selectivity can be impactful is in epoxide ring opening (ERO) reactions. ERO reactions with alcohols can form either a terminal ether or terminal alcohol. Terminal ethers can be used in polyether polyols and epoxy resin synthesis and terminal alcohols are desired for epoxide oligomerization. These reactions can be catalyzed by Lewis acid zeolites that involve heteroatoms such as tin incorporated into the framework.
Sn-MFI and Sn-Beta are two main Sn-zeolites who have been shown to have high selectivity for the terminal ether when ring opening epichlorohydrin with methanol. As the epoxide is changed to epoxyoctane, Sn-Beta maintains a high activity, but with a decrease in selectivity. However, Sn-Beta is less selective for other epoxides including styrene oxide. Interestingly, Sn-MFI is highly selective for ring opening styrene oxide suggesting that shape selectivity is a potential design constraint. In our ongoing work, we investigate the effect of framework type, CHA, MFI, Beta, and FER, on selectivity for alcohol ring opening of epoxides. Elucidating the effects of zeolite framework type on regioselectivity for ERO reactions will reveal a new structure-activity relationship to help design Lewis acid zeolites with improved catalytic performance.
