SYNTHESIS AND CHARACTERIZATION OF THE MCM-22 ZEOLITE

MCM-22 has been synthesized as a unique phase and with good crystallinities in a range of different SiO2/Al2O3 ratios using hexamethylenimine as a template. For SiO2/Al2O3 ratios around 30, MCM-22 can be obtained as a pure phase and with good yields in a relatively broad range of OH/SiO2 ratios, although the efficiency in Si incorporation decreases with increasing pH. For low Al2O3 contents (SiO2/Al2O3 greater than or equal to 70) the sample becomes contaminated by ZSM-5. This contamination can be eliminated by lowering the crystallization temperature. If the synthesis is carried out under static conditions, ferrierite also appears in the crystallized sample. Upon calcination to eliminate the organic template, some dealumination occurs, while strong acid sites are formed, pyridine being accessible to all hydroxyl groups associated to framework Al. This together with the large void volume of the zeolite suggest the presence of a multidirectional system of channels where at least some of the channels are formed by large pores.