Aromatization of Isophorone to 3,5-Xylenol over Cation-Exchanged Granulated Hierarchical Yh Zeolites

A series of catalysts were prepared from a granulated hierarchical (micro–meso–macroporous) NaYh zeolite: NaYh, H-NaYh, H-Yh, Li-NaYh, K-NaYh, Ca-NaYh, Mg-NaYh, and La-NaYh. Their physicochemical properties were characterized, and their catalytic activity and product selectivity were investigated in the aromatization of isophorone. The highest performance in the synthesis of 3,5-dimethylphenol was achieved in the presence of K-NaYh, the catalyst distinguished both by the highest basicity among the tested samples and by low concentrations of weak Brønsted acid sites and Lewis acid sites. This sample exhibited a 3,5-dimethylphenol selectivity of 78.6% at an isophorone conversion of 98.9%. H-Yh, H-NaYh, Ca-NaYh, Mg-NaYh, and La-NaYh provided the highest possible isophorone conversion (up to 100.0% at 400°C and 1 h–1), with the reaction products mainly consisting of dimethylbenzenes and trimethylbenzenes (their selectivity reached up to 72.9 wt %). In the presence of low-activity samples (NaYh and Li-NaYh), the predominant products were methylbenzenes (dimethylbenzenes and trimethylbenzenes, 26.6–30.9%) and isophorone derivatives (β-isophorone and dihydroisophorone, 30.5–33.0%).