Characterization and catalytic activity of MCM-22 and MCM-56 compared with ITQ-2

MCM-22, MCM-56 and ITQ-2 zeolites! have been characterized by different physicochemical techniques (XRD, Si-29 MAS NMR, IRI adsorption, and catalytic test), and they show that the first two are similar in structure and reactivity while ITQ-2 is different. The external surface area of the MCM-56 sample is somewhat larger than MCM-22 both being much smaller than ITQ-2. This is in agreement with the 15-20% larger adsorption capacity for 1,3,5-trimethylbenzene shown by MCM-56 with respect to MCM-22 and the seven times larger adsorption shown by ITQ-2 This is a consequence of a higher degree of disorder along the c axes in MCM-56 than in MCM-22. A similar type of disorder, i.e., the same XRD pattern than for MCM-56, was observed after adsorbing acetone on the laminar precursor of MCM-22. The external surface acidity of the three samples, as measured by 2,6 ditertbutylpyridine (26 DTBPy), follows the order ITQ-2 > MCM-56 > MCM-22 and this is reflected by the catalytic activity towards a large molecule (1,3,5-triisopropyldenzene) which can react only at the external surface (external cups) of these materials. (C) 2000 Academic Press.