A range of mesoporous sulphated zirconias with tuneable structural and catalytic properties have been prepared by direct impregnation. The surface sulphate coverage can be readily varied, achieving a maximum value of similar to0.2 monolayers. High-temperature calcination induces the crystallisation of tetragonal zirconia while suppressing the monoclinic phase and enhances surface acidity. Superacid sites only appear above a critical threshold SO4 coverage of 0.08 mL (corresponding to 0.44 wt% total S). Sulphated zirconias show good activity towards alpha-pinene isomerisation of under mild conditions. Conversion correlates with the number Bronsted acid sites, while the selectivity towards mono- versus polycyclic products depends on the corresponding acid site strength; superacidity promotes limonene formation over camphene. (C) 2003 Elsevier Science (USA). All rights reserved.