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.
