VAPOR-PHASE NITRATION OF BENZENE OVER MODIFIED MORDENITE CATALYSTS

Active and stable mordenite catalysts have been developed for the sele ctive nitrobenzene production by vapour-phase nitration of benzene wit h 65 wt.-% HNO3 at normal pressure and 443 K. The acidic and textural properties of commercial synthetic mordenite have been modified by dif ferent combinations of thermal and acid treatments. The physico-chemic al properties of the catalysts were investigated by Al-27 and Si-29 MA S-NMR, AAS, XRD, N-2 and low pressure Ar adsorption. The catalytic act ivity and stability of the modified mordenite catalysts were strongly influenced by the amount and state of aluminium in the zeolite. Extra- framework aluminium species generated by thermal treatment at higher t emperatures (greater than or equal to 973 K) induced a severe catalyst deactivation. The deactivation could almost be eliminated by subseque nt acid leaching with 6 N HCl, which removed the extra-framework alumi nium to a large extent, thus unblocking the pores and/or pore mouths. An optimum mordenite modification procedure was developed, resulting i n highly active and selective catalysts, which retained their initial activity for at least 120 h on stream.