Study of CO2 adsorption on a commercial CuO/ZnO/Al2O3 catalyst

The interaction between CO2 and a commercial CuO/ZnO/Al2O3 (CZA) catalyst has been investigated by employing temperature-programmed desorption (TPD), FTIR spectroscopy and equilibrium adsorption-desorption experiments. TPD runs were carried out after exposure of the reduced or oxidized catalyst to a CO2-containing gaseous stream at temperatures of 25, 200 and 300 degrees C. Equilibrium CO2 adsorption-desorption experiments were performed up to 2 MPa at 25, 50, 100, 200 and 300 degrees C. In addition, the formation of carbonate species following adsorption at room temperature and at high temperatures (200, 300 degrees C) has been investigated via in situ FTIR experiments in a DRIFTS cell. CO2 adsorption revealed extensive surface heterogeneity as indicated by: i) the shape of TPD profiles, ii) the fact that no standard model (Langmuir, Freundlich and others) could provide a good fit with random distribution of residuals and physical meaning of estimated parameter values and iii) the non-linear Clausius-Clapeyron plots at all coverages. CO2 adsorption at high temperatures takes place through creation of new adsorption states on both oxidized and reduced catalysts corresponding to polydentate carbonates at the expense of other surface carbonates. The presence of hysteresis between adsorption-desorption isotherm branches indicates that a fraction of CO2 adsorbs irreversibly on oxidized CZA.