Influence of Li loading on the catalytic performance of Li/MgO in the oxidative dehydrogenation of propane to olefins

A series of Li/MgO catalysts with different Li loadings were prepared by incipient wetness impregnation method and characterized by TG-DTA, N₂ sorption and XRD; two modes for propane adsorption on Li/MgO were considered by calculation with Material Studio and the influence of Li loading on the catalytic performance of Li/MgO in the oxidative dehydrogenation of propane to olefins was investigated. The result indicated that with the increase of Li loading, the conversion of propane and the selectivity to C₂H₄, C₂H₆, CH₄, CO_x increases at first, reaches the highest values at a Li loading of 3% and then decreases with further increasing the Li loading, whereas the selectivity to propene changes in an opposite trend. The adsorption and dehydrogenation of propane on Li/MgO surface are controlled by both thermodynamic and kinetic factors, whilst the dispersion of the active Li⁺O^- sites is related to the loading of Li. Over the highly-dispersed active Li⁺O^- sites, the dehydrogenation is thermodynamically controlled, which favors the formation of propene, whereas over the poorly-dispersed Li⁺O^- sites, the reaction is dominated by the kinetic factor, leading to a high selectivity to ethene and other by-products.