The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst

The promoting effect of niobium in a Li/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidattve dehydrogenation of ethane (ODHE) has been studied in some detail. it has been found that a Li/Nb/MgO catalyst with 16 wt % niobium showed the highest activity for the C, production in the OCM reaction; the activity at 600 “C was ten times that of the Li/MgO catalyst at the same temperature. The Li/Nb/MgO catalyst was also slightly more active for the ODHE reaction than was the Li/MgO catalyst. However, the Li/Nb/MgO catalyst produced considerably more carbon dioxide in the both reactions, Structural investigation of the catalyst showed that the addition of niobium to the Li/MgO catalyst increased the surface area and gave an increase in the lithium content of the caicined catalysts. Two niobium phases, LiNbO, and Li,NbO,, were formed; it is shown that the first of these probably causes the increased activity. Ageing experiments showed that the activity of the catalyst was lost ff the catalyst was used above 720 “C, the melting point of the lithium carbonate phase. The catalyst showed a decrease of surface area after ageing and a sharp decrease of the amount of the two niobium phases. The addition of carbon dioxide to the feed could not prevent the deacttvation’of the Li/Nb/MgO catalyst.