Characterization of activated carbon using X-ray photoelectron spectroscopy and inelastic neutron scattering spectroscopy

The surface chemistry of a commercial activated carbon (Sutcliffe DCL 230), which is representative of carbons used as support materials in finely divided metal catalysts, has been characterized by a combination of traditional methods (surface area, porosity, Boehm titration, adsorption studies) supplemented by X-ray photoelectron spectroscopy (XPS) and inelastic neutron scattering (INS) spectroscopy. pH measurements show the carbon to be highly acidic, with Boehm titration and XPS suggesting a high proportion of carboxylic and lactonic surface groups. Adsorption of phenylacetylene and benzonitrile was followed by I-TV-vis spectroscopy to determine the affinity of the carbon for substituted aromatics. INS was carried out on the as-received material and also after the adsorption of pyridine on the carbon surface, which was used as a probe of surface acidity. Pyridine chemisorption yielded an excellent INS spectrum, which closely matched solid pyridine, indicating a relatively weak interaction between the carbon and the pyridine. The INS spectrum also confirmed that the number of acid sites capable of protonating pyridine was below an upper limit of 5.6 x 10(19) (g of carbon)(-1). Collectively, this work emphasizes the amphoteric nature of the carbon studied, albeit with a strong acid bias, and indicates that bulk acidity is a poor description of the carbon's chemisorption characteristics.