(349c) Mechanism and Site Requirements for Parallel Dehydration Reactions of Ethanol Over Proton-Form Zeolites

Steady state, transient and isotopic chemical reaction studies were used to probe the effects of zeolite pore size and connectivity on parallel dehydration pathways of ethanol to form ethylene and diethyl ether. The conversion of ethanol to diethyl ether was largely independent of ethanol partial pressure on all proton-form zeolites (FER, MFI, and MOR) suggesting that the dehydration of ethanol dimers at saturation coverage controls diethyl ether production rates. Ethylene production via monomolecular ethanol dehydration reactions was only observed on H-MOR because small 8-MR side pockets prevent the formation of bulky ethanol dimers and result in the selective stabilization and dehydration of ethanol monomers via reaction sequences that appear zero order in ethanol pressure. These conclusions are consistent with the low rates of ethylene production on zeolites without OH groups in 8-MR channels (MFI, BEA) wherein the absence of spatial constraints leads to the predominant prevalence of energetically favorable ethanol dimer intermediates that inhibit the formation of ethanol monomers which are required for ethylene production.