Phosphate, as catalytic promoter of zirconia, has similar effects as sulfate and tungstate anions, i.e., enhanced thermal stability with high retention of surface area and higher crystallization temperature, in comparison with unpromoted zirconia, n-butane isomerization activity increases and selectivity to isobutane decreases as phosphate content increases. For n-heptane isomerization, activity and selectivity to iota-C-7 have maxima.