Factors affecting the stability and selectivity of zeolites in the conversion of methanol to hydrocarbons. Communication 1. Effect of heat treatment in steam

Abstract

1. Thermal steam treatment of ZSM zeolites leads to their dealuminization, but the crystal structure is retained. 2. When the steam-treatment temperature is increased to 600°C, as a first step aluminum is lost from the cation positions and probably from the locations where it is concentrated in the framework; this leads to a reduction in secondary reactions and hydrogen transfer reactions and, as a result, to an increase in the resistance of the zeolite to coking. 3. When the steam-treatment temperature is increased to 600°C, the overall number of active centers falls sharply and hence also the degree of conversion of methanol to hydro-carbons. The active centers which remain are uniform.