The formation of carbocations on SZO is generally inferred to be a result of a "superacidic" Brønsted site. Because SZO is a mild Brønsted acid, reactions with alkanes through traditional mechanisms encountered with liquid 34 or solid superacids are not possible. A Brønsted acidity argument also neglects plausible reaction pathways that could be mediated by strong Lewis acids present in superacids. In this case, the pyrosulfate site serves as a reservoir of adsorbed SO3 on the SZO surface that facilitates reversible hydride abstraction of sp 3 hybridized C-H bonds to form carbocations that can undergo subsequent reaction chemistry. Pyridine and TEPO are common acidity probes. Both probes form strong adducts that are (essentially) irreversible on surfaces, and both provide a spectroscopic readout for the quantity and strength of acid sites. Related calorimetry studies were described by Drago and Kob using pyridine to determine acid strength of sites present on SZO. Those studies found that pyridine binds to a strong acid site with an energy of 31.2 kcal mol -1 , close to the value calculated for adduct formation between the pyrosulfate and pyridine described here.