Impact of the residual chlorine on the heat of adsorption of the linear CO species on Cu/Al2O3 catalysts

The adsorption of CO at several adsorption temperatures (T-a) in the range of 300-550 K on several reduced; 5 wt % Cu/Al2O3 solids, with and without residual chlorine, is studied by FTIR spectroscopy. Whatever the solid, the main adsorbed species is a linear (denoted by L CO species adsorbed on Cudegrees sites. On the Cl-free solids, the L CO species is detected at 2095 cm(-1), while the presence of Cl leads to a shift to higher wavenumbers. The evolution of the coverage theta(L) Of the L CO species with the adsorption temperature for a constant CO partial pressure (P-CO = 1 kPa) allows us to determine the heat of adsorption of the L CO species as a function of the coverage on the various Cu-containing solids by using the AEIR method. It is shown that the presence of residual Cl has no impact on the heat of adsorption at low coverages (82 kJ/mol), while it decreases slightly the heat of adsorption at high coverages from 57 to 45 kJ/mol.