Variation of the surface properties of nickel oxide upon heat treatment evidenced by temperature programmed desorption and inverse gas chromatography studies

The surface properties (dispersive component γSdof surface energy and surface nanomorphology) of nickel oxide samplessubmitted to heat treatments up to 550°C were examined bytemperature programmed desorption (TPD) and inverse gaschromatography (IGC) methods. It is shown that the variation ofγSd is complex, first increasing as thetemperature reaches about 300°C, then decreasing and goingagain through a maximum, of lower amplitude, for a treatmenttemperature of about 600°C. These variations follow closelythe TPD curves that related the rate of H2O and, in a much lesserextend of CO2 releases as the heat treatment temperature augments.The surface nanomorphology changes also during this treatment. TheNiO surface becomes very interactive when treated around 250°C. The determination of the adsorption energy distributioncurves (energetic heterogeneity) clearly demonstrates the change insurface properties and development of the population of highadsorption energy sites. Rehydration of the sample treated at 300°C was not possible under our experimental conditions.