The structure of the new pure silica zeolite RUB-24, Si 32O 64, obtained by topotactic condensation of the intercalated layer silicate RUB-18

Abstract

Zeolite RUB-24 was prepared by heating a precursor phase, the intercalated layer silicate R-RUB-18 (R = alkylammonium cations) in air at 500 °C. The microporous silica framework of RUB-24 forms by topotactic condensation of the silicate layers of the crystalline precurser R-RUB-18. A Rietveld structure refinement of X-ray powder diffraction data of RUB-24 which was performed in space group I4 1/amd confirmed the topology of the structure model. RUB-24, Si 32O 64 per unit cell ( a 0 = 7.6677 (2) Å, c 0 = 27.063 (1) Å) is a new small pore zeolite with a one-dimensional pore system consisting of straight and non-intersecting 8-ring channels. The structure represents a new zeolite framework type (the code assigned by the International Zeolite Association is RWR) having a high framework density of 19.2 T/1000 Å 3 (with respect to idealized cell parameters). Although the structure analysis showed that the pores of the (idealized) silica framework are empty, nitrogen sorption experiments showed that there is no “free” access to the pore volume. According to 29Si MAS NMR spectroscopy a few defects are present caused by incomplete or random condensation of the silanol groups which might block access to the pores.