Template removal from molecular sieves by low-temperature plasma calcination

Abstract

The oxidative removal of templates from crystals of MFI- and TON-type zeolites using low-temperature oxygen plasma at 370 K has been investigated. This treatment removes tetrapropylammonium inside 5 µm lengths of channels in the completely siliceous MFI structure (silicalite), and diethylamine to a depth of at least 70 µm in the channels of the completely siliceous TON structure. Substitution of B, Al or Fe into the framework of silicalite significantly obstructs the removal of tetrapropylammonium, but complete decomposition of the template can be accomplished in small samples of [Si, B]-MFI. A comparison of plasma calcination with thermal calcination in air indicates that the release of boron into extra-framework positions upon either treatment is caused by the slow desorption of water at the calcination temperature.