BOROALUMINOSILICATE CATALYSTS WITH THE ZSM-5 STRUCTURE SYNTHESIZED IN NONALKALINE MEDIA

Aluminosilicate and borosilicate (containing up to 3.80 B atoms per unit cell) zeolites with the ZSM-5 structure have been prepared by the "fluoride route" and studied by a range of techniques. Contrary to numerous studies (which investigated the conversion of methanol at much higher temperatures), trans-but-2-ene and not ethylene is the first hydrocarbon desorbed from the catalyst at temperatures below 200-degrees-C. We propose a mechanism for this reaction which does not require the formation and desorption of ethylene to the gas phase. The reaction of the methoxy intermediate formed on an acid site with the CH3OH molecule gives surface ethoxy groups, which are alkylated by further methanol molecules to give propoxy and butoxy groups.