CO desorption kinetics from clean and sulfur-covered Ru(001) surfaces

Abstract

The desorption of CO from clean and sulfur-covered Ru(001) surfaces was studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. CO was observed to desorb from clean Ru(001) with coverage-dependent kinetics. The isothermal desorption of CO was monitored with LITD measurements. The rates for CO desorption were determined using a simple Padé approximant method to evaluate coverage-dependent kinetic parameters. On the clean Ru(001) surface, the desorption activation energy and preexponential dropped sharply from Ed=34 kcal/mol and νd=5×1015s−1 for ΘCO<0.33 ML to Ed=23 kcal/mol and νd=2×1012s−1, for ΘCO>0.33 ML. The clean Ru(001) surface results agreed very well with earlier studies of CO desorption. The presence of surface sulfur shifted the TPD peaks for CO on Ru(001) to lower temperatures. Likewise, isothermal LITD measurements revealed that the CO desorption parameters at ΘCO=0.06 ML decreased from Ed=36 kcal/mol and νd=1×1016s−1 to Ed=22 kcal/mol and νd=5×1010s−1 as the sulfur coverage increased from ΘS=0.00 to 0.24 ML. The kinetic parameters derived from the isothermal LITD experiments were able to predict accurately the CO TPD spectra as a function of CO coverage, sulfur coverage and heating rate. The dramatic effect of sulfur on the CO desorption kinetics at low sulfur coverages argued for a long-ranged electronic effect for sulfur interacting with CO on Ru(001).