Friedel–Crafts alkylation of toluene with tert-butyl alcohol over Fe2O3-modified Hβ

Abstract

Fe₂O₃ (x)/Hβ catalysts with different Fe₂O₃ loadings (x) were successfully prepared and characterized by XRD, SEM, TEM, ICP, BET, NH₃-TPD and Py-IR. With selective alkylation of toluene with tert-butyl alcohol to produce 4-tert-butyltoluene as a probe reaction, the effects of the different Fe₂O₃ loadings on channel structures, acidity and catalytic performance over Hβ were studied. The results showed that modification of Hβ with Fe₂O₃ could adjust pore structures and decrease the total acidity, especially the strong acidity of Hβ. The parent Hβ exhibited the highest toluene conversion of 58.4% with the lowest PTBT selectivity of 67.3%. The low para-selectivity over parent Hβ could be attributed to the low shape-selective action of 12-ring portals of Hβ and the isomerization of the formed PTBT to MTBT. Upon loading of Fe₂O₃, the toluene conversion of Fe₂O₃ (x)/Hβ catalysts decreased slightly, but the PTBT selectivity increased significantly. A toluene conversion of 54.7% with PTBT selectivity of 81.5% was observed over Fe₂O₃ (20%)/Hβ at 190 °C after 4 h. The narrowed pores after loading the Fe₂O₃ were beneficial to increasing the selectivity to PTBT, since PTBT with a lower kinetic diameter (0.58 nm) can diffuse through the narrowed pores of Fe₂O₃ (x)/Hβ more easily than MTBT (0.65 nm). In addition, the decrease in number of strong acid sites and deactivation of acid sites on the surface are beneficial to increasing the selectivity to PTBT by suppressing further isomerization of the formed PTBT on acid sites.