Ziff-Gulari-Barshad model with reactive sulfur: Mean field approximation and Monte Carlo simulations.

In this work, we propose and study an extension of the Ziff-Gulari-Barshad (ZGB) model for heterogeneous catalysis that incorporates sulfur (S) alongside the reactive gaseous species CO and O_{2}. By accounting for the formation and desorption of SO_{2} and COS, this model introduces reactions that alter the system's dynamic behavior. Through Monte Carlo simulations and site mean-field (SMF) approximations, we characterize the steady-state phase diagram which now presents new S-rich absorbing phases. We introduce an aggregation factor in the SMF approach to recover the continuous phase transition that is typically absent in standard mean-field treatments. Our results indicate that the second-order transition line between the active and the pure O absorbing phase remains belonging to the directed percolation universality class. Notably, we observe a promotion effect where small concentrations of sulfur enhance CO_{2} production by approximately 5% when compared to the pure ZGB model. This phenomenon is attributed to the efficient creation of vacant sites by sulfur-oxygen reactions, which optimizes the surface coverage and prevents CO poisoning.