Ethanol to Aromatics on Modified H-ZSM-5 Part II: An Unexpected Low Coking.

In this study a commercial H-ZSM-5 zeolite (Si/Al=11) was post-synthetically modified by a combined dealumination procedure to adjust its catalytic properties for the selective formation of aromatics from ethanol. The solid-state properties of original and modified zeolites are determined by structural, textural and acidity analysis. The formation of aromatics and durability of the zeolites were investigated depending on space velocity or contact time in the catalyst bed. In particular, the formation rate and desorption of aromatics from solid-state surface as well as their tendency to form coke precursors by consecutive build-up reactions determine the formation of coke. Therefore, the rate of build-up and finished aromatization by hydride transfer (pre-determined by the kind, location and geometric arrangement of surface acid sites) and the statistical number of reaction events until final desorption at the specific contact time have to be harmonized to increase aromatics yield and to decrease catalyst decay by coke simultaneously.