(704h) Effect of Dopants on the Activity and Selectivity in the Oxidative Coupling of Methane over Rare Earth Oxides

The oxidative coupling of methane (OCM) is a potential pathway to convert methane directly to highly valuable ethylene, as well as other hydrocarbon products. However, it is very difficult to obtain high yields of C₂₊ products (i.e. products such as ethane, ethylene and higher hydrocarbons), due to the formation of thermodynamically more stable higher oxidation products, such as CO and CO₂ (CO_x). It is well known that rare earth oxides (REOs), such as samaria (Sm₂O₃) and lanthana (La₂O₃), are amongst the most efficient single component oxide catalysts in the oxidative coupling of methane, while reducible REOs (e.g. ceria, terbia, and praseodymia) are typically more selective towards CO_x products than C₂₊ products. However, we have in the past shown that addition of lithium to non-reducible rare earth oxides can significantly alter their activity and selectivity in the OCM reaction. For example, Li-doped terbia supported on MgO is not only more active and selective compared with the reference Li/MgO, Sm₂O₃/MgO and Li-Sm₂O₃/MgO catalysts, it is also more stable in the OCM reaction with time on stream. We have extended the investigation of doped rare earth oxides to include also transition metal dopants and report their effects on the OCM reaction.