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

Abstract

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.