Further investigations on the synthesis of pure-silica molecular sieves via the use of organic structure-directing agents

Abstract

Several organic structure-directing agents (SDAs) that are variations of a 4,4′-trimethylenebis(N-methyl, N-R₁-piperidinium) moiety were synthesized and used for the synthesis of pure-silica molecular sieves. Pure-silica MTW, MFI, BEA and the MCM-41-type mesoporous materials could be prepared by changing only the R₁ group. When R₁ was pentyl or hexyl, MFI was crystallized, suggesting that each SDA molecule spans two channel intersections. For R₁ groups smaller than pentyl, MTW was formed. Pure-silica BEA could easily be prepared when R₁ was benzyl or cyclohexylmethyl. Numerous variations of the organics used to crystallize BEA were explored and the features necessary to structure direct the formation of BEA elucidated. When R₁ was either octyl or nonyl, the MCM-41-type mesoporous materials were formed, indicating that these organics can act as surfactants. The results presented provide further evidence that organic molecules can serve as structure-directing agents for the synthesis of pure-silica molecular sieves.