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Two groups of samples were studied for the aromatization of methane over Mo-Fe/ZSM-5 catalysts. The first group contains fixed loading (5 wt%) and variable Mo/Fe ratio. The second group was prepared with fixed Mo/Fe ratio and variable loading. The samples were characterized by TGA, S BET , XRD, NH 3 -TPD and TPO analysis. NH 3 -TPD results indicate that the strength of strong acid sites increases when Mo/Fe ratio decreases for samples with fixed loading. The amount of strong sites decreases and new intermediate acid sites appear on samples containing both Mo and Fe. XRD results show the presence of iron molybdate for samples impregnated with both Mo and Fe. The catalytic properties of these samples were related not only to the amount and strength of acid sites but also to the iron molybdate phase.

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The catalytic decomposition of methane over M-Co-Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S BET , TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750°C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co 3 O 4 at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co 3 O 4 and CoAl 2 O 4 due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu-Co alloy. In the reaction carried out at 700°C, the observed activity was Co-Al [ Mg-CoAl [ Ni-Co-Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu-Co-Al sample, which produced mostly amorphous carbon.

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