Kinetics of desorption, adsorption, and surface diffusion of CO 2 on MgO(100)

Abstract

The kinetics of desorption, adsorption, and surface diffusion of CO 2 on a single crystal MgO(100) surface were investigated using laser induced thermal desorption (LITD) techniques. Isothermal and linear temperature ramp LITD experiments revealed that the CO 2 desorption from MgO(100) followed coverage-dependent first order kinetics. Assuming a preexponential of v = 1 × 10 13 s -1, the desorption activation energy varied from E d = 9.4 to E d = 7.1 kcal/ mol as a function of surface coverage. This coverage dependence suggested repulsive interactions between adsorbed CO 2 molecules. Adsorption experiments revealed an initial sticking coefficient that decreased with increasing surface temperature. This behavior was in quantitative agreement with the predictions of a simple precursor-mediated adsorption model. LITD measurements of surface diffusion indicated a surface diffusion coefficient for CO 2 on MgO(100) at 100 K that was below the limits of detection of the LITD experiment. These results allowed an upper bound of D ⩽ 1 × 10 −9 cm 2/s to be assigned for the surface diffusion coefficient of CO 2 on MgO(100) at 1