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 °C). 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.