Unraveling the contribution of structural phases in Ni-Nb-O mixed oxides in ethane oxidative dehydrogenation

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• 作者：Z. Skoufa ; E. Heracleous ; A.A. Lemonidou
• 关键词：Ethane oxidative dehydrogenation ; Nickel-based mixed oxides ; Solid solution ; Temperature programmed oxygen desorption ; CO-temperature programmed reduction
• 刊名：Catalysis Today
• 出版年：2012
• 出版时间：30 September, 2012
• 年：2012
• 卷：192
• 期：1
• 页码：169-176
• 全文大小：1151 K

文摘

The role of each structural phase present in highly active and selective Ni_0.85Nb_0.15 catalyst in ethane oxidative dehydrogenation is investigated. Based on previous studies, Ni_0.85Nb_0.15 consists of a Ni-Nb solid solution and a Nb-rich amorphous phase. A series of Ni-based mixed oxides with low Nb content simulating the Ni-Nb solid solution and an amorphous Nb-rich sample were synthesized and studied separately. The catalytic tests demonstrated that the introduction of even a tiny amount of Nb (atomic ratio: Nb/(Ni + Nb) = 0.01) leads to a drastic increase in ethylene selectivity (150 % ) compared to pure NiO. Selectivity gradually increases with increasing Nb loading up to 15 % , in parallel with the decrease in oxygen desorbed as measured by O₂-TPD. Based on the results of combined catalytic testing and physicochemical characterization, Ni-Nb solid solution can be identified as the key component for the high ethylene selectivity of the Ni_0.85Nb_0.15 catalyst, as the insertion of even a small amount of Nb drastically decreases the electrophilic oxygen species responsible for the total oxidation reactions. Co-existence of the Ni-Nb solid solution with the amorphous Nb-rich phase does not influence significantly the catalytic properties of the material.