On the stability of VPI-5, a large pore molecular sieve

Abstract

An important advance in molecular sieve technology was achieved in 1988 when M E Davis and his co-workers at the Virginia Polytechnic Institute reported the synthesis of VPI-5, the first molecular sieve having uniform pores of greater than 1nm diameter. It seems that no attempt has been made to make a systematic study of the stability of the VPI-5 structure. However, recent work by the authors has indicated that the adsorptive properties, the stability and the removal of water are all inter-connected and need to be considered if VPI-5 is to be used as a selective adsorbent or catalyst support. The work summarised here was undertaken on a sample of VPI-5 kindly provided by Professor M E Davis. A definitive explanation of these results cannot be reached without further work, but it seems likely that changes in the channel structure are brought about by the removal of the highly ordered zeolitic water (and possibly to some extent by the re-entry of water). The irreversibility of the Type I isotherms is an indication of activated entry effects which may be the result of partial pore blockage of the large unidimensional pores which would be expected to allow free access to all the adsorbate molecules studied.