Sorption properties of modified silicoaluminophosphate(SAPO)-5 and SAPO-11molecular sieves

The pore structures of silicoaluminophosphates (SAPO), SAPO-5, SAPO-11 and their transition metal substituted modifications were studied by physisorpt ion of nitrogen at 77 K. The pore volume distributions in these materials w ere computed by applying the expanded form of the BJH equation to the N-2 d esorption data. The N-2 adsorption-desorption hysteresis loops, the pore vo lume distributions and other physical properties show that these molecular sieves contain nonuniform pores spreading over a wide range of pore radii u pto 300 Angstrom with appreciable contributions from micropores (pore radii < 2 nm) to pore volumes of a majority of them. The generation of mesopore structures in these materials with different surface areas should be attrib uted to the changes in structures and textures brought about by evolution o f water vapour and oxides of carbon and to the mobility of cations during c alcination at 500<degrees>C in air to remove organic template after hydroth ermal synthesis and drying. An attempt is made to correlate the physical pr operties of the catalysts to the ionic radii of the cations substituted in them. The probable influence of these cations on the reactivity of the surf aces of the metal substituted SAPO-5 molecular sieves is assessed by normal izing the activities of the catalysts in the reaction between I-naphthol an d methanol to produce 2-methyl-1-naphthol and 1-methoxy naphthalene with re spect to surface areas. (C) 2001 Elsevier Science B.V. All rights reserved.