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, COx 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.