IR investigation of the oxidation of propane and likely C3 and C2 products over group IVB metal oxide catalysts

In-situ infrared spectroscopy was used to examine the gas phase and adsorbed species formed during the oxidation of propane gas on ZrO(2), TiO(2), and CeO(2) catalysts, versus a reference Pt/Al(2)O(3) Catalyst, in the absence and presence of an oxygen atmosphere. The same examination was applied to a number of likely oxidation products, namely, 2-propanol, acetone, and acetic acid (vapor phase). Both examinations were carried out as a function of temperature (up to 400 degreesC). The results obtained could help in assigning the oxidation pathway and surface sites, which are considered extendable to metal oxide surfaces containing no excess oxygen species. A number of important conclusions were, accordingly, arrived at, the most prominent of them being: (i) the initial catalytic interaction is the oxidative dehydrogenation of propane into propene, rather than the oxidative addition into 2-propanol; (ii) the catalytic activity of the test oxides (ZrO(2) < TiO(2) < CeO(2)) appears to be directly related to the oxide reducibility and surface acidity; (iii) the catalytic active sites are Lewis acid-base pair sites over which the secondary carbon C-H bond is activated by simultaneous bonding, and the hydrogen abstraction is facilitated by the reducibility of the Lewis acid site; (iv) CeO(2) is a promising catalytic material for the total oxidation of hydrocarbons.