Sulfated zirconium oxide (SZO) is an enigmatic material with a rich and complex history. Selected properties are described in Figure . Initial reports showed that SZO forms isobutane from butane at lower temperatures than oleum, which was attributed to Brønsted "superacid" sites on this material. Implicit in this proposal is that carbocations form by protonation of butane to form carbocations, analogous to liquid superacids. However, DFT studies of fully dehydrated ZrO2 showed that H2SO4 heterolytically dissociates to form Zr-(OH)-Zr Brønsted sites near bound sulfate anions, which are mild Brønsted acids from gas phase acidity calculations. This is supported by experimental studies showing that SZO does not protonate p-nitroaniline in MeCN slurry (pKa(anilinium) = 6.22 in MeCN). Though mild, the Brønsted sites on SZO participate in reactions with organometallics to form well-defined ion-pairs where the sulfate behaves as a weakly coordinating anion. SZO also shows pronounced redox activity. Lercher and Sauer showed that butane adsorbs onto SZO to form butenes, and careful measurement of byproducts formed during butane isomerization detected SO2 as a byproduct. DFT calculations also showed that the overall reaction of pyrosulfates and butane to form sulfate, SO2, H2O and butene is exothermic. The butene generated in this reaction was proposed to react with the mild Brønsted sites on SZO to form the supported carbocation ion (or alkoxide) that rearranges to isobutane. This result also explains why butene promotes the butane isomerization reaction. A mechanistically related reaction was reported by Delferro and Kaphan in reactions of Cp*IrPh(Me)(PMe3) reacts with pyrosulfate sites on sulfated alumina. In this case, single electron transfer from Cp*IrPh(Me)(PMe3) to a pyrosulfate forms a [SO3•][SO4 -] site that abstracts an H-atom from the Cp* ligand. The latter example is the closest to the pyrosulfate opening to transient SO3 and SO4 2- sites proposed here.