TEMPERATURE-PROGRAMMED CO2 HYDROGENATION OVER A LI-NI-CO-O CATALYST MONITORED IN-SITU BY AC ELECTRICAL PARAMETERS COUPLED TO MULTIPLE-ION MONITORING OF THE PRODUCT SPECIES

Product analysis with temperature increasing between 573 and 873 K has been studied for carbon dioxide hydrogenation. A non-stoichiometric m ixed oxide, Li0.9Ni0.5Co0.5O2-delta was investigated. The exit gas str eam was monitored by using the multiple-ion monitoring facility of a q uadrupole mass spectrometer. The a.c. electrical characteristics of th e catalyst pellet between 100 Hz and 1 MHz were simultaneously monitor ed in situ. A clear correlation between catalytic behaviour and electr ical properties was obtained. Surface dipole effects during chemisorpt ion, and reaction phases, were revealed. At the lower frequencies, des orption of the gases at 873 K resulted in a decrease in both conductan ce and capacitance until desorption was completed, as shown by the dec ay curves on the mass spectrometer. As a result of the chemical reacti on, the catalyst becomes partially reduced, as shown by the changes in conductance-temperature-frequency characteristics. The reaction was c ompared between the freshly oxidized material and the catalyst in the reduced state. Its original oxidized state could be recovered by re-ox idation at 973 K for 1 h in air.