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 ${\mathrm{O}}_2$. By accounting for the formation and desorption of ${\mathrm{SO}}_2$ 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 ${\mathrm{CO}}_2$ 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.

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• Directed percolation
• Nonequilibrium statistical mechanics
• Phase diagrams