Reactions for the partial oxidation of propane over Pt-on-Ceria

The sequence of reactions for the formation of hydrogen from propane has been studied using a supported 1% Pt catalyst, with either a low-surface-area CeO(2) or a high-surface-area CeO(2) as support. The catalytic experiments were carried out in a fixed-bed reactor at 600 degrees C at different contact times. Flow rates were varied (100, 200, 300, and 400 sccm), as were the catalyst loadings (0.01 g and 0.02 g). Six species (CO, H(2), CO(2), C(3)H(8), C(3)H(6) and O(2)) were analyzed at the exit of the reactor. Using the Gauss-elimination procedure, it was found that the number of independent reactions is four. A material balance of the exit species can be used to determine a set of independent reactions which are physically meaningful under a given set of conditions. (Of course, dependent reactions are obtained by algebraic manipulations of the independent reactions chosen.) The set of reactions comprising partial oxidation, total oxidation, water formation and dehydrogenation is a possible sequence of reactions for the low-surface-area catalyst. For the high-surface-area catalyst, the same set of reactions is also a possibility for the 0.01 g loading, but not for the 0.02 g loading. For that case, there is a net loss of water, so the water-formation reaction in the set above is replaced by the water-gas-shift (WGS) reaction. The net loss of water is shown to be due to the effect of the ceria support. To confirm the choice of the above sets, independent runs involving WGS, dry reforming and steam reforming were carried out over the catalysts. Neither dry reforming nor steam reforming can take place in appreciable amounts over any of the catalysts, while WGS occurs over the catalyst with the largest total surface area. This is consistent with the choice of reaction sets above. Finally, the nature and relative importance of the reactions in these sets indicate that the amount of propane reacting via partial oxidation increases with loading and also with flow rate, while the amount of propane reacting via total oxidation increases only slightly with loading and decreases with flow rate. This implies that partial oxidation takes place first, as compared to total oxidation. Microreactors, with small contact times, would be preferred for such processes. (C) 2010 Elsevier B.V. All rights reserved.