SYNTHESIS AND CHARACTERIZATION OF THE MCM-22 ZEOLITE

MCM-22 has been synthesized as a unique phase and with good crystallin ities in a range of different SiO2/Al2O3 ratios using hexamethylenimin e as a template. For SiO2/Al2O3 ratios around 30, MCM-22 can be obtain ed 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 o r equal to 70) the sample becomes contaminated by ZSM-5. This contamin ation can be eliminated by lowering the crystallization temperature. I f the synthesis is carried out under static conditions, ferrierite als o appears in the crystallized sample. Upon calcination to eliminate th e organic template, some dealumination occurs, while strong acid sites are formed, pyridine being accessible to all hydroxyl groups associat ed to framework Al. This together with the large void volume of the ze olite suggest the presence of a multidirectional system of channels wh ere at least some of the channels are formed by large pores.