I.r. spectroscopic study of CO2 adsorption onto η-Al2O3

Abstract

The adsorption of CO₂ at room temperature onto η–Al₂O₃ dehydrated at various temperatures between 25 and 800°C was studied by i.r. and microgravimetric techniques. The following surface species are formed; three σ-coordinated linear structures, two bicarbonates that can be interconverted, several “organic” carbonates and minor amounts of mono- and bi-dentate carbonates. Relative concentrations of these species depend strictly on pretreatment conditions, while the nature of the species is primarily determined by the coordination of surface cations. The overall coverage is quite small, (θ⩽ 10 %) and nearly the same as in all transition aluminas. A cooperative mechanism for CO₂ adsorption is thus invoked to account for this and other features. The interaction between CO₂ adsorption and catalytic activity is considered, and the probable nature of the centres responsible for exchange and equilibration reactions is suggested.