Transformation of ethylbenzene-m-xylene feed over MCM-22 zeolites with different acidities

• Zeolite MCM-22 samples were studied in the transformation of EB-m-xylene feed.
• Acidity was modified by steam-dealumination/acid treatment and B substitution.
• B-containing sample shows EB conversion of 40% at less than 5% xylene loss.
• It has also high selectivity to p-xylene production at 723 K.
• Catalysts dealuminated by steaming and acid treatment were not effective.

Transformation of ethylbenzene (EB, 22 wt%)-m-xylene (78 wt%) mixture was carried out over zeolite MCM-22 catalysts with different acidities. The modification of the number and strength of the acid sites was attained by: (i) dealumination by steaming and successive acid treatment and (ii) isomorphous substitution of framework Al for boron ([Al,B]MCM-22). The effect of platinum introduction was also investigated. The strong decrease in the Brønsted acidity, concomitant to the dealumination procedure, appears unfavorable since it leads to a drastic diminish of the degree of EB conversion, not compensated by satisfactory level of m-xylene isomerization. [Al,B]MCM-22 is a modification with much better performance, most probably because it contains both strong, Al-connected acid sites but in lower amount than in the parent sample, and weaker boron-generated sites and practically no any Lewis sites.Parent zeolite [Al]MCM-22 as well as B-substitution possess promising properties for ethylbenzene-m-xylene mixture transformation catalyst with adequate degree of EB conversion and extent of p-xylene approach to equilibrium as well as low xylene loss.

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