The role and stability of Li₂O₂ phase in supported LiCl catalyst in oxidative dehydrogenation of n-butane

This study was aimed at defining the role of active phases in supported LiCl and LiCl-DyCl₃ catalysts in the catalytic oxidative dehydrogenation (ODH) of n-butane. LiCl supported on silica displayed the highest activity and selectivity in n-butane ODH compared with other alkali metal halides. Addition of DyCl₃ increased the activity. TPO, XRD and Raman light scattering (RLS) data showed that LiCl and DyCl₃ formed during the preparation stage were converted to Li₂O₂ and DyOCl phases, respectively, by calcination in air at >400°C. The results of separate TPR experiments (O₂-oxidation-butane reduction) along with XRD, RLS and X-ray photoelectron spectroscopy (XPS) data proved that butane reacts mainly with oxygen species of Li₂O₂ phase at ODH conditions, probably attributed to [Li⁺O^-] pairs. The proposed functions of chlorine and dynamic oxygen in the ODH of butane are consistent with the activity, selectivity and stability of silica and magnesia-supported catalysts. High thermal stability of Li₂O₂ in oxidized LiCl catalyst was attributed to the formation of protective Li₂O·LiCl surface layer. Deactivation of LiCl/SiO₂ catalyst in n-butane ODH is caused by the formation of Li-silicates at reaction conditions while LiCl/MgO display a stable performance.