SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF MWW TYPE ZEOLITE ITQ-1, THE PURE SILICA ANALOG OF MCM-22 AND SSZ-25

The synthesis of pure silica MWW type zeolite ITQ-1 using trimethylada mantammonium (TMAda(+)) is described. The reproducibility of the synth esis, as well as the duality of the materials obtained, is greatly imp roved if the synthesis is assisted by hexamethyleneimine (HMI) as a se cond organic additive. As TMAda(+) is too large to fit into the sinuso idal 10 MR channel (i.e., the channel delimited by a ring of 10 tetrah edra), the stabilization of this channel seems to require the presence of additional organic moieties. In the absence of HMI, these probably come from either the partial degradation of TMAda(+) or from organics adsorbed on the PTFE liners in previous syntheses. The use of TMAda() and HMI and Na+ cations allows a fast and highly reproducible synthe sis of pure silica ITQ-1. The material obtained shows an improved crys tallinity in both the as-made and the calcined form. The structure of calcined ITQ-1 has been refined in space group P6/mmm (a = 14.2081(1) Angstrom, c = 24.945(2) Angstrom, R-exp = 0.103, R-wp = 0.159, R-f = 0 .065), using synchrotron powder diffraction data, and the topology pre viously proposed for the aluminosilicate MCM-22 zeolite has been confi rmed. Comparison of the highly resolved Si-29 MAS NMR spectra of as-ma de and calcined ITQ-1 show that in the as-made form there is a high co ncentration of Si-OH defect groups, which are annealed upon calcinatio n and which arise from a lack of connectivity between specific Si site s.