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

RSC Advances Pub Date: 2016-10-26 DOI: 10.1039/C6RA21054F

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.

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