By using the multiple ion-monitoring facility of a quadrupole mass spectrometer, the on-line analysis of species has been studied for temperature programmed methane coupling over a non-stoichiometric mixed oxide Li0.9Ni0.5Co0.5O2-delta catalyst between 400-800 degrees C. The effects of water vapour, methane and oxygen were also separately studied. The a.c. electrical characteristics of the catalyst pellet between 100 Hz and 1 MHz were simultaneously monitored in-situ. Catalytic changes are immediately reflected in changes in the a.c. characteristics. Frequency dependent a.c. losses due to surface dipole effects dominate during phases of strong chemisorption and reaction, whilst reversion to thermally activated behaviour occurs during regions of reduced chemical activity. Lattice oxygen is able to act as a source of oxygen and react with methane. The oxidative coupling of methane showed stable behaviour for 3h at 750 degrees C.