EFFECT OF SULFUR ON THE DECOMPOSITION KINETICS OF METHANOL ON RU(001)

The effects of sulfur on the decomposition kinetics of methanol on Ru(001) were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. TPD studies showed that molecular desorption became more probable as a function of sulfur coverage. In addition, no new surface pathways were observed to compete with the primary pathway involving decomposition to carbon monoxide and hydrogen. Isothermal LITD studies of methanol decomposition were performed at methanol coverages of θ < 0.04θsat for various temperatures from 188 to 223 K. These LITD measurements revealed that the methanol decomposition rate was very dependent on sulfur coverage. Both the decomposition activation barrier and preexponential were observed to increase versus sulfur coverage. The coverage-dependent decomposition rate versus sulfur coverage was fit to k = v010(cθs) exp[-(E0 + aθCO + bθS)/RT] where E0 = 6.9 kcal/mol, v0 = 4.2×106 s-, a = 35 kcal/(mol ML), b = 27 kcal/(mol ML) and c = 13 ML-1. The increase in the decomposition activation barrier and preexponential were qualitatively consistent with the electron withdrawing properties and long-ranged electronic effects of surface sulfur. © 1990.