Using in situ C-13 MAS NMR, it has been demonstrated that propane is carbonylated with carbon monoxide to produce isobutyraldehyde and isobutyric acid at 100-150degreesC on sulfated zirconia. Isobutyraldehyde represents the intermediate reaction product, which is almost completely converted into the acid at 150 degreesC. The selective formation of isobutyraldehyde at low temperatures on SZ indicates that principally the secondary C-H bond of propane is activated, rather than its C-C bond. This pathway of the alkane activation can be realized either on Lewis acid sites of SZ or by direct formylation by the formyl cation formed as equilibrated species from the formate. Infrared spectroscopy provides evidence that the sulfate groups of SZ are responsible for the aldehyde oxidation. The formation of surface dithionate species as a result of sulfur reduction is suggested. These dithionate species are readily reconverted into sulfate groups by an oxidizing treatment in an O-2 atmosphere. (C) 2004 Elsevier Inc. All rights reserved.