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Coke remaining from the partial burning of coke deposited during the commercial re-forming of naphtha on a Pt-Re/ Al203 catalyst was studied. Burning temperatures were 623-923 K, and the remaining coke was characterized by temperature-programm ed oxidation, X-ray diffraction, electron diffraction, ffi, 13C CP-MAS NMR, electron spectroscopy for chemical analysis, electron paramagnetic resonance, and chemical analysis. After coke is burned at 673 K, the residual coke shows the minimum value in the H/C ratio and the maximum in the thickness of the aromatic layers, degree of or ganization, C=O concentration, binding energy of C ls, peak width, and g value. This agrees with the model of coke burning: at low temperatures, the burning is selective; the more hydrogenated and amorphous carbonaceous species are burnt first. At high temperatures, the burning is nonselective and all species are simultaneously burnt. Coke is partiall y oxidized during burning, and intermediate species with C=O and C-OH groups are formed.

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Different mono (Pt), bi (Pt±Sn, Pt±Pb, Pt±Ga) and trimetallic (Pt±Sn±Ga) catalysts based on Pt and supported on different materials (Al 2 O 3 , Al 2 O 3 ±K and ZnAl 2 O 4 ) were tested under severe process conditions in the propane dehydrogenation reaction (both in continuous and in pulse reactors). Results show that the Pt±Sn±Ga/ZnAl 2 O 4 catalyst has a better and more stable performance in propane dehydrogenation (high yield to propene and low coke deposition), than the other bi-and trimetallic systems and a commercial catalyst. Thus, the use of an adequate support (ZnAl 2 O 4 ) in combination with the addition of Ga to the Pt±Sn bimetallic system enhances the catalytic performance. INTRODUCTIONThe selective propane dehydrogenation to propene is a very important industrial process since it produces a valuable raw material for polypropene manufacture. This process can be carried out by using supported metallic catalysts, though several dif®culties should be avoided in order to develop catalysts with a good performance. In this sense, both the inhibition of hydrogenolysis and cracking reactions, and the minimisation of the coke deposition, are major requirements in order to increase the selectivity to propene and the catalytic stability. From the development of the STAR Process, 1 different bimetallic supported systems have been studied in this reaction. The utilisation of non-acidic and thermal stable supports, such as MgAl 2 O 4 or ZnAl 2 O 4 , 2±4 appears as an important factor in order to increase the stability of the metallic phase during successive operational cycles. Besides, the addition of Sn to Pt improves alkene formation and reduces coke deposition. 5 Hence, both the selection of an adequate support and the composition of the metallic phase can be considered as relevant factors in order to develop better catalysts for this process.In this paper, the behaviour of different catalysts (Pt, Pt±Sn, Pt±Ga, Pt±Pb and Pt±Sn±Ga supported on Al 2 O 3 , K±Al 2 O 3 and ZnAl 2 O 4 ) in the propane dehydrogenation reaction are compared with a commercial catalyst used for dehydrogenation of alkanes on an industrial scale. The effects of the three different supports and the addition of several inactive metals of