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MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective oxidation of propane to acrylic acid and in the oxidative dehydrogenation of ethane to ethylene. The influence of the concentration of oxalate anions in the hydrothermal gel has been studied for two series of catalysts, Nb-free and Nb-containing, respectively. Results show that the development of an active and selective active orthorhombic phase (Te 2 M 20 O 57 , M = Mo, V, Nb) requires an oxalate/Mo molar ratio of 0.4-0.6 in the synthesis gel in both types of samples. The presence of Nb favours a higher catalytic activity in both ethane and propane oxidation, and a better production of acrylic acid.

Mixed Ni-W-O catalysts (with a W/(Ni ? W) atomic ratio of 0.3) supported on c-Al 2 O 3 or on mesoporous alumina have been prepared, characterized and tested in the oxidation of ethane. For comparison unsupported and supported NiO as well as bulk Ni-W-O mixed oxides catalysts have also been studied. Supported Ni-W-O materials show interesting catalytic performances in the oxidative dehydrogenation of ethane. They show similar catalytic activities than the corresponding unsupported Ni-W-O catalysts.However, the selectivity to ethylene over supported catalysts was higher than that achieved over unsupported samples (the selectivity to ethylene followed the trend: mesoporous-supported [ c-Al 2 O 3 -supported [ unsupported Ni-W-O). In addition, it has also been observed that Ni-W-O catalysts are more efficient than the corresponding W-free NiO catalysts. The discussion of the catalytic results will be undertaken on the basis of the modification of active sites of NiO when incorporating WO 3 and/or metal oxide supports.

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