A TEMPERATURE-PROGRAMMED ISOTOPE-EXCHANGE STUDY OF CA-NI-K AND MG-LI OXIDE CATALYSTS USED FOR OXIDATIVE COUPLING OF METHANE

A temperature programmed isotope exchange (TPIE) technique was used to study the isotope exchange between gas phase oxygen and lattice oxygen of two Ca-Ni-K oxide, and a Mg-Li oxide catalysts at temperatures up to 750°C. Two types of active surface sites were found: one responsible for single exchange between gas phase oxygen and lattice oxygen and the other responsible for multiple exchange between gas phase oxygen and lattice oxygen. The multiple exchange reaction takes place at lower temperature than the single exchange reaction. The number of active sites responsible for multiple exchange of oxygen is only a fraction (<20%) of that responsible for single exchange. The amount of lattice oxygen exchanged by gas-phase oxygen depends on both the nature of the catalyst and exchange temperature. At temperatures ≤750°C, Mg-Li oxide has the highest exchange capacity (>20%). Ca-Ni-K (A) oxide prepared from the corresponding nitrate and Ca-Ni-K (B) oxide made by physical mixing of CaO, NiO, and KNO3 have a comparable amount (∼10%) of lattice oxygen exchanged by gas phase oxygen. © 1993 by Academic Press, Inc.