Alkylation of catechol with methanol to give guaiacol over sulphate-modified zirconia solid acid catalysts: The influence of structural modification of zirconia on catalytic performance

Sulphated zirconia catalysts were synthesized by wetness impregnation of Zr(OH)4 with (NH4)2SO4 solution. The samples were characterized by XRD, FTIR, BET and TPD (NH3 adsorption measurements). The catalysts were tested for the methylation of catechol in a fixed-bed reactor at 200 °C and 1 bar pressure. Calcination facilitated the transformation of ZrO2 from the tetragonal to monoclinic and addition of SO42- to Zr(OH)4 helped to retain the tetragonal phase through a surface complex phase. A direct correlation was observed between catechol activity and total acidity. The 5-wt% SO42-/ZrO2 catalyst showed the best conversion (∼80%) and selectivity for guaiacol (83%). Small addition of water in the feed improved the stability of the catalyst.