Competitive adsorption of oxygenates and aromatics during the initial steps of the formation of primary olefins over ZSM-5 catalysts

Abstract

Aromatics present during the early stages of MTO conversion compete for active sites with the educts, oxygenates (methanol, DME), in primary olefin formation over ZSM-5 catalysts. This competitive adsorption is investigated using TPD and TPSR in a TAP reactor. DME induces methanol desorption at lower temperatures. Diphenylethane desorbs at higher temperatures than toluene. Microkinetic simulations show that toluene, methanol, diphenylethane and DME have activation energies of desorption of 107, 112, 119 and 121 kJmol−1 on strongest binding sites respectively. DME has the highest surface coverage and is suggested as the key surface oxygenate responsible for direct primary olefin formation.