The effect of activation and calcination conditions on the activities of Fe-and Mn-promoted sulfated zirconia (MFSZ) catalysts for the isomerization of n-butane at low temperatures (less than or equal to 90 degrees C) was investigated. Activation in air resulted in a higher activity of MFSZ than did activation in helium; this is in contrast to the situation for unpromoted sulfated zirconia (SZ) catalysts where the activation atmosphere did not affect the activity. The maximum activity of MFSZ was found to occur when the activation temperature was 450 degrees C, while for unpromoted SZ, the optimum activation temperature was 250 degrees C. Comparison of the n-butane conversions at these two temperatures showed that MFSZ was only about 1.6 times as active as SZ. This activity difference is much less than that reported before in the literature where comparison was made at the same activation temperature. This activity difference is attributed to the different degree of synergism between redox and acid sites on the two catalysts.