Synthesis and characterisation of zeolites using saturated cyclic amines as structure-directing agents

Abstract

A synthesis route to obtain high-silica MOR using cyclic amines as structure-directing agents is described. As far as we know, the use of these structure-directing agents for the synthesis of high silica MOR is not described elsewhere. The pore size of the synthesised products (zeolite MOR, FER and mixtures of zeolite MOR and FER), was related to the ring size of the organic structure-directing agent in the reaction mixture. Various saturated cyclic amines were used. Pure high-silica MOR of high crystallinity was obtained via direct synthesis using hexa- and heptamethyleneimine. In addition, high-silica FER was prepared among others with pyrrolidine. A mixture of MOR and FER was synthesised in the presence of piperidine. The materials were characterised and the catalytic performance of the high silica MOR was evaluated. Catalysts prepared with direct synthesis of high-silica MOR as base material were active in the isomerisation of pentane and hexane. Presumably the direct-synthesis high-silica MOR samples were somewhat less active than conventional MOR (dealuminated by leaching to the same Si/Al ratio SAR), because of a lower accessibility of acid sites. The lower accessibility of the direct synthesis mordenite may be due to amorphous material. Other explanations are that extra-framework aluminum species were formed during calcination and preferential aluminium siting in these MOR crystals.