Methylation of phenol over ion-exchanged β-zeolites

Zeolite-β, synthesized hydrothermally, was Lewis acid ion exchanged with Zn(II), Ga(III), La(III) and Ce(III) metal ions by wet chemical method. They were characterised by XRD, IR, MAS NMR, BET, ICP and TPD techniques. Vapour phase alkylation of phenol with methanol over these catalysts was studied at 523, 573, 623, 673 and 698 K. The products obtained were o-cresol, 2,6-xylenol and anisole. Phenol conversion decreased with increase in temperature over all the catalysts due to blocking of active sites by coke. Selectivity to o-cresol decreased with increase in temperature but the same for its dependent product, 2,6-xylenol, increased with increase in temperature. Selectivity to anisole also decreased with increase in temperature due to its conversion to o-cresol. Increase of weight hourly space velocity (WHSV) increased selectivity to anisole and decreased selectivity to 2,6-xylenol and o-cresol. The study of time on stream indicated blocking of strong acid sites by coke and hence these site dependent formation of 2,6-xylenol was largely reduced.