Transformation of aromatic hydrocarbons over isomorphously substituted UTL: Comparison with large and medium pore zeolites

Abstract

Isomorphously substituted UTL zeolite with heteroatoms Al, Ga and Fe was synthesized, characterized by X-ray powder diffraction, scanning electron images, nitrogen adsorption isotherms and pyridine adsorption followed by FTIR spectroscopy and tested in disproportionation of toluene, toluene alkylation with isopropyl alcohol and trimethylbenzene disproportionation/isomerization. The catalytic properties of UTL zeolites were compared with those of BEA and MFI zeolites and the observed differences are discussed. Isomorphously substituted (Al, Ga, Fe) UTL zeolites show in most cases lower conversions for the reactions studied but higher selectivities to more valuable products. For toluene disproportionation reaction UTL zeolites shown higher selectivity to xylenes compared with BEA and MFI. In toluene alkylation with isopropyl alcohol no n-propyltoluenes are formed over (Ga)UTL or (Fe)UTL while some traces of this undesired product were observed over (Al)UTL. (Al)UTL shows high selectivity to cymenes and iso-/n-propyltoluene ratio orders of magnitude higher than for MFI. The initial selectivity to xylenes in trimethylbenzene disproportionation/isomerization decreases in the order (Ga)UTL>(Al)UTL≈BEA≫MFI and correlates with increasing of acid centres strength, showing that isomorphously substituted extra-large pore zeolites can be enough active and more selective catalysts in some aromatic hydrocarbon transformation reaction.