A first-principles based microkinetic simulation of the role of sulfur in controlling surface chemistry of CO reactions on Fe surface*

 

 

A combination of density functional theory and microkinetic are used to study clean and defective iron surfaces as well as surfaces with CO, S, CO+S adsorbates with the aim of investigating the effect of S as an inhibiting agent in the carburization process of Fe. The structural properties as well as the adsorption energetics of these systems are calculated and analyzed. The presence of S is found to reduce the adsorption energy of CO on Iron hence lowering the sticking and dissociative probabilities. Our investigation looks to determine if the blocking effect acts at a short- or long-range. We subsequently employed a microkinetic model based on rate equations for the elementary steps and take into account adsorption energetics, coverage, partial pressure and temperatures at typical operation conditions involved in a carburization environment. Results from our model provide insights into the effect of these variables and how they can be manipulated to control the reaction of CO on Fe surface. The calculated kinetic results show that CO adsorbs in molecular state up to 440 K from where it dissociates into C and O atoms. The introduction of sulfur increases the dissociation temperature to 650 K emphasizing the effect the addition on sulfur has on the reactivity of carbon monoxide on Fe surface. These simulations show how density functional theory combined with microkinetic simulations offer insight in to complex chemical processes for catalytic reactions.