Generalized Evaluation of the Effect of SO₂ Adsorption-Modulated <i>d</i>-π* Back-Donation Activation on Transition Metals

SO2 adsorption significantly affects the d-electron structure of transition metal catalysts, thereby altering their d-π* activation capability for molecules with abundant antibonding orbitals (e.g., NO, CO, etc.). However, a universal theoretical framework for systematically evaluating the effect of SO2 adsorption on the activation ability of transition metal surfaces is still lacking. This study proposes a method to comprehensively evaluate the response characteristics of different transition metals to SO2 adsorption, based on the modulation effects of SO2 adsorption on the work function (WF) and d-band center (ED–EF). The ΔWF and Δ(ED–EF) values, normalized by surface volume, can be used to establish a systematic criterion for assessing the impact of SO2 adsorption on the d-π* activation capability of molecules on transition metal surfaces. Preliminary validation of this method was conducted through crystal orbital Hamiltonian population (COHP) calculations for C≡O bonds and adsorption property analysis of CO molecules. This research provides a clear theoretical basis for designing novel sulfur-tolerant catalysts and offers guidance for optimizing practical catalytic systems, such as selective catalytic reduction (SCR) for NOx removal, three-way catalytic (TWC) reactions, CO oxidation, and many other processes.