VAPOR-PHASE NITRATION OF BENZENE OVER MODIFIED MORDENITE CATALYSTS

Active and stable mordenite catalysts have been developed for the selective nitrobenzene production by vapour-phase nitration of benzene with 65 wt.-% HNO3 at normal pressure and 443 K. The acidic and textural properties of commercial synthetic mordenite have been modified by different combinations of thermal and acid treatments. The physico-chemical properties of the catalysts were investigated by Al-27 and Si-29 MAS-NMR, AAS, XRD, N-2 and low pressure Ar adsorption. The catalytic activity 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 temperatures (greater than or equal to 973 K) induced a severe catalyst deactivation. The deactivation could almost be eliminated by subsequent acid leaching with 6 N HCl, which removed the extra-framework aluminium to a large extent, thus unblocking the pores and/or pore mouths. An optimum mordenite modification procedure was developed, resulting in highly active and selective catalysts, which retained their initial activity for at least 120 h on stream.