Infra-red studies of carbon monoxide and hydrocarbons adsorbed on silica-supported nickel

Abstract

Infra-red studies of NH3, HCl, CO, C2H4, and butene adsorbed on transparent aerogels were made to elucidate the surface chemistry of nickel/silica and the nature of adsorbed species. In addition to the hydroxyl band found on silica at 3750 cm–1, most “dry” nickel/silica aerogels exhibited a band near 3620 cm–1, apparently caused by silanol groups near nickel ions. Reduction of all nickel ions by H2 treatment proved very difficult. Nickel ions remaining on “reduced” gels were apparently the acid sites that adsorbed NH3 strongly. Chemisorption of HCl showed that reactive oxide ions, not found on silica, were also present. Bands between 1800 and 2210 cm–1 showed at least 7 types of adsorbed CO, varying in relative importance with the extent of reduction. Three distinct ionic sites for CO adsorption appeared to exist. Bands near 2200 cm–1 arose from CO on the sites which held NH3 most strongly, implying binding to a nickel ion. Reaction of HCl with these sites, however, showed that they also contain oxide ions.Adsorption of ethylene on “reduced” nickel/silica produced 1- and 2-butenes which were quickly converted to butane on subsequent addition of H2. Spectra ascribed by others to associatively adsorbed ethylene ([graphic omitted]H2—[graphic omitted]H2) and to ethyl groups on reduced nickel probably instead show butenes and butane.