LOW-TEMPERATURE OXIDATIVE DEHYDROGENATION OF ETHANE OVER CATALYSTS BASED ON GROUP-VIII METALS

Unsupported Fe, Co and Ni catalysts are active in the oxidative dehydr ogenation of ethane (ODHE) at low temperature. A conversion of 1% is a chieved at 585, 438 and 487 K, respectively. The selectivity towards e thylene is found to be ca. 60% at low conversion. As the reaction temp erature increases, the selectivity remains nearly constant for Ni whil st it decreases for Fe and Co. This behaviour has been explained by co mparing the catalytic properties of Co and Ni towards ethane and ethyl ene oxidation. The ODHE intrinsic activity sequence (Co>N>Fe) is simil ar to that observed for the homomolecular exchange of oxygen, confirmi ng that these catalysts are in an oxidized state in the course of the ODHE reaction. The study of the reduction and oxidation of unsupported and silica-supported nickel catalysts using magnetic methods has show n that the catalytic activity is not related to the ease of the Ni2+-N i-0 transition. TAP experiments carried out over Ni have revealed that the oxygen species involved in the reaction are irreversibly held by the catalyst at 573 K (possibly O-) from which a reaction mechanism is proposed. Furthermore, this series of experiments have shown that eth ane is irreversibly adsorbed and that CO2 originates from a parallel-c onsecutive scheme. (C) 1997 Elsevier Science B.V.