IR Investigation of the Oxidation of Propane and Likely C₃ and C₂ Products over Group IVB Metal Oxide Catalysts

Abstract

In-situ infrared spectroscopy was used to examine the gas phase and adsorbed species formed during the oxidation of propane gas on ZrO2, TiO2, and CeO2 catalysts, versus a reference Pt/Al2O3 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 (ZrO2 < TiO2 < CeO2) 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) CeO2 is a promising catalytic material for the total oxidation of hydrocarbons.

A comparative study of the photocatalytic oxidation of propane on anatase, rutile, and mixed-phase anatase–rutile TiO2 nanoparticles: Role of surface intermediates

“…4 can be readily identified with the acetone (2984, 1680-1690, and 1245 cm −1 ), R-COO − species, and formate species in particular (∼1500-1600 and ∼1350-1380 cm −1 ) [8,9,11,17,24,29,[40][41][42][43][44][45]. In what follows, we scrutinize the spectral information in detail and identify key surface intermediates on each sample.…”

“…Table 2 Compilation of infrared absorption bands and vibrational mode assignment of the major adsorbed species on TiO 2 formed during photocatalytic degradation of propane. Assignments are based on the reported DRIFT data in the present study and the following references: [8][9][10]18,19,21,24,29,[40][41][42]45,47] TiO 2 polymorph Surface specie Mode description Frequency (cm −1 )…”

Catalysts for selective propane oxidation in the presence of carbon monoxide: Mechanistic aspects

“…Taking a closer look, there is also a very small signal at 1585 cm À1 . This band can be assigned to the antisymmetric mode of m(CAO) of carboxylate species [26,30]. Since these bands are very weak, we conclude that the adsorption of propane plays no role at these conditions.…”

“…Only one small band at 1709 cm À1 is visible. In the literature, bands in this range are assigned to m(C@O) indicating that oxidized propane species such as acetone or propionaldehyde may form [26][27][28][29]. The intensity of the m(C@O) stretching mode is very low, and other stretching modes of this species are not detectable.…”

TiO2–Al2O3 as a support for propane partial oxidation over Rh

“…This improvement is attributed to the presence of more oxygen-containing support on TiO 2 (TiO 2 , has 2 oxygen atoms per Ti) compared to Al 2 O 3 (which has 1.5 oxygen per Al atom). Catalytic activity, particularly over mixed oxides, depends upon oxide reducibility and surface acidity [23]. These properties of the oxides can alter the oxidative mechanism of the primary feed component.…”