Product analysis with temperature increasing between 573 and 873 K has been studied for carbon dioxide hydrogenation. A non-stoichiometric mixed oxide, Li0.9Ni0.5Co0.5O2-delta was investigated. The exit gas stream was monitored by using the multiple-ion monitoring facility of a quadrupole mass spectrometer. The a.c. electrical characteristics of the catalyst pellet between 100 Hz and 1 MHz were simultaneously monitored in situ. A clear correlation between catalytic behaviour and electrical properties was obtained. Surface dipole effects during chemisorption, and reaction phases, were revealed. At the lower frequencies, desorption of the gases at 873 K resulted in a decrease in both conductance and capacitance until desorption was completed, as shown by the decay curves on the mass spectrometer. As a result of the chemical reaction, the catalyst becomes partially reduced, as shown by the changes in conductance-temperature-frequency characteristics. The reaction was compared between the freshly oxidized material and the catalyst in the reduced state. Its original oxidized state could be recovered by re-oxidation at 973 K for 1 h in air.