Oxidative dehydrogenation of ethane to ethylene over Ni-Nb-M-O catalysts: Effect of promoter metal and CO2-admixture on the performance

Ni-Nb-O based catalysts are known for high activity and selectivity for the oxidative dehydrogenation of ethane (ODHE) to ethylene at relatively low temperatures. The parent Ni-Nb-O catalyst used in this work showed an ethylene yield of 32%. This solid was further modified by three promoters each, i.e. Cr, Mo, W, that belong to the same group of elements but showing different d-characters. This aim of such modification is to further improve activity and/or selectivity. However, the catalytic results of the doped solids revealed somewhat reduced activity compared to the parent Ni-Nb-O catalyst during ODHE. BET surface area data, reducibility, acidity characteristics as well as near-surface composition of Ni-Nb-M-O showed considerable deviations, which however depend upon the nature of promoter doped. The near-surface region Ni/Nb ratio is the key parameter for tuning the catalytic properties of the solids. Among the three modifiers used, Cr displayed relatively superior catalytic performance compared to other two yielding in an ethane conversion of 26% and an ethylene selectivity of ca. 65%. Nonetheless, the introduction of CO2-admixture into the reactant feed mixture improved the selectivity of ethylene in ODHE. Ni-Nb-Cr-O solid in particular revealed an enhanced ethylene selectivity of ca. 85% at slightly reduced ethane conversion. (C) 2015 Elsevier B.V. All rights reserved.