Abstract
Three samples of (Si,Ga)-MCM-22 zeolites (IZA code MWW) with Si/Ga ratios of 18, 71 and 89 were synthesized hydrothermally under static conditions, using hexamethyleneimine as a structural directing agent (SDA). The pure phase of zeolite was obtained only for Si/Ga = 18, while for the other ratios one unknown phase was detected. SEM, XRD, TG-ATD, BET, 71Ga and 29Si NMR MAS spectroscopies were performed, confirming the isomorphous substitution of gallium into the zeolite structure. The acidic properties were studied by TPD of ammonia, showing that the acid character depends on the gallium concentration. The catalytic performances of (Si,Ga)-MCM-22 zeolite with various Ga contents were studied in the toluene disproportionation reaction in the temperature range 573-673 K. We showed that the fraction of p-xylene increases with the isomorphous substitution degree and decreases with the temperature and also that the catalytic performances are correlated with the structure and the acidic properties of the (Si,Ga)-MCM-22 zeolite.