MEASUREMENT OF STATE OF METAL DISPERSION ON SUPPORTED NICKEL CATALYSTS BY GAS CHEMISORPTION

Gas chemisorption has been investigated as a technique for the estimation of the state state of nickel dispersion on supported nickel hydrocarbon conversion catalysts. Published chemisorption studies on nickel catalysts are critically reviewed. Catalysts which were examined included nickel on alumina and nickel zeolites. Gas chemisorption measurements were supplemented by X-ray diffraction line-broadening determinations to establish the average nickel crystallite sizes. Nickel areas estimated from hydrogen chemisorption at 250°C at a hydrogen vapor pressure of 100 mm mercury and from average nickel crystallite size determined by X-ray diffraction line-broadening were in good agreement. These results provide strong evidence that dissociative hydrogen adsorption occurs only on nickel crystallites of sufficient size to offer adjacent hydrogen adsorption sites. Carbon monoxide chemisorption at room temperature at a carbon monoxide vapor pressure of 100 mm mercury, after correction for carbon monoxide adsorption on the support, provides the more accurate measure of total nickel area including nickel in an atomic state of dispersion. A combination of hydrogen chemisorption or X-ray diffraction line-broadening measurement, plus carbon monoxide chemisorption, can be used to estimate the relative amounts of nickel in comparatively large crystallites (∼50 Å) and in an essentially atomic state of dispersion, as well as the specific surface area of the nickel in these two size ranges. © 1968 Academic Press Inc.