A DFT Study of the Adsorption and Dissociation of CO on Sulfur-Precovered Fe(100)

Sulfur is known to be a poison to several catalytic reactions, e.g., the Fischer-Tropsch synthesis (FTS), in which it affects drastically the performance of both iron- and cobalt-based catalysts. However, despite the importance of this industrial process, little is known about what elementary steps are poisoned by sulfur. In the present article, we report, using d. functional theory, the effect of sulfur on one of the most relevant reactions in the FTS: the dissocn. of carbon monoxide over iron surfaces. We have studied the adsorption and dissocn. of CO on Fe(100)-S-p(2 * 2) (qS = 0.25 ML) and on Fe(100)-S-c(2 * 2) (qS = 0.50 ML). We have found surface configurations that correlate well with the desorption features obsd. in temp.-programmed desorption mass spectroscopy. In addn., we have calcd. the activation energy of CO dissocn. on Fe(100)-S-p(2 * 2), which, interestingly, is very similar to the activation energy of CO dissocn. on the sulfur-free Fe(100) surface. However, the sign of the reaction changes by the presence of sulfur; CO dissocn. is highly exothermic on the sulfur-free Fe(100) surface, whereas on the Fe(100)-S-p(2 * 2) surface, it is slightly endothermic. Moreover, according to our results, the influence of sulfur in the CO dissocn. seems to be short-ranged. [on SciFinder (R)]