Dual-edged sword effects of sulfation/hydration on Ce-doped TiO2(001) single-atom catalyst for NH3-SCR reaction: A first-principles study

SO2/H2O-resistance remains challenges for selective catalytic reduction with NH3 (NH3-SCR). The detailed promotion and/or inhibition effects of sulfation/hydration on cerium-titanium (CT) catalysts for NH3-SCR are still controversial. Herein, a series of adsorption characteristics, bonding strengths, electronic effects, and reaction pathways were performed by first-principles density functional theory calculations to explore the structure-performance/resistance of CT catalysts and unravel the effects of sulfation/hydration for NH3-SCR. We constructed six CT catalyst structures based on three TiO2 facets [(0 0 1)/(1 0 1)/(1 0 0)] and two surface configurations [single-atom (SA)/interface (IF)]. CT(0 0 1)-SA could protect the active Ce site from sulfation/hydration with TiO2(0 0 1) as SO2/H2O-trapping site, which was the optimal SO2/H2O-resistant structure among six CT catalyst structures. An electron-deficient state of CT(0 0 1)-SA was caused by sulfation/hydration through electron capture behavior. From the perspective of reactants adsorption, this electron-deficient state not only promoted the NH3/NO adsorption but also suppressed the secondary sulfation/hydration. As for NH3-SCR pathways, hydration promoted NH3 dissociation, N-N coupling, and N-O breaking, but inhibited the H1 transfer (rate-determining step). Sulfation impaired the redox ability of Ce site, promoted H1 transfer and N-O breaking, but inhibited the NH3 dissociation, N-N coupling, and H2 transfer (rate-determining step). Hence, sulfation/hydration exhibited “dual-edged sword” effects for NH3-SCR on CT(0 0 1)-SA via electronic effects.