Influence of the synthesis conditions of H-ZSM-5 on its physical properties and catalytic activity in methanol conversion: the water content of the reaction mixture

Abstract

The effects of the water content of the reaction mixture on the physicochemical properties and the performance of ZSM-5 type zeolite catalysts in methanol conversion reactions were investigated. The average diameter of the zeolite crystallites increased as the water content in the reaction mixture increased. The bulk silica-alumina ratio remained constant though the water-silicon ratio of the reaction mixture was varied from 7.8 to 80. In contrast, the silica-alumina ratio at the outer shell of the crystallites decreased as the water content of the reaction mixture increased. In the methanol conversion at 540°C, the zeolite synthesized from the reaction mixture with the lowest water-silicon ratio showed the longest catalytic life. This was attributed to the slowest rate of coke formation over it. It was concluded that lowering the aluminum content at the outer shell of the crystallites by lowering the water content of the reaction mixture depressed the coke deposition and improved the catalyst stability.