Mechanistic Insights into the Atomic-Level Synergy of NiRu Single-Atom Alloy on ZrO2 for Efficient Photocatalytic CO2 Methanation and Biogas Upgrading

Atomic-level modulation of transition metal nanoparticles through single-atom hetero-doping provides a promising strategy for optimizing catalytic reaction. However, a fundamental understanding of the underlying reaction mechanism remains elusive. In this study, we present Ni ₁₀ –Ru ₁ /ZrO ₂ as a model photocatalyst, where isolated Ru atoms are anchored on Ni nanoparticles to form a single-atom alloy (SAA) supported on ZrO ₂ . Aberration-corrected STEM and in situ EXAFS analyses reveal that Ru atoms are atomically dispersed on the Ni nanoparticle (~ 3 nm) surface and maintain a stable coordination environment ( N _{N i} ₋ _{N i} = 6.5, N _{R u} ₋ _{N i} = 3.9) throughout the reaction. Photocatalytic evaluation, in situ XPS and XAFS demonstrate the synergistic bimetallic interaction and photothermal effect in Ni-Ru SAA, optimizing the electronic structure and charge carrier dynamics. Combined with ¹³ CO ₂ -labeled in situ FTIR and DFT calculations, the results show that the isolated Ru sites facilitate the accumulation of the key intermediate *CO and promote its dynamic migration to neighboring Ni sites, thereby reducing the activation barrier of the rate-determining step *CO to *HCO by 0.26 eV, creating an optimal environment for CO ₂ activation. Under UV–visible light irradiation, SAA Ni ₁₀ –Ru ₁ /ZrO ₂ exhibits outstanding performance for CO ₂ hydrogenation to CH ₄ , achieving the production rate of 7.2 mmol g⁻ ¹ h⁻ ¹ with nearly 100% selectivity, 12-fold and 105-fold higher than that using monometallic Ni ₁₀ /ZrO ₂ and Ru ₁ /ZrO ₂ , respectively. Additionally, its potential in biogas CO ₂ methanation is demonstrated for upgrading, highlighting its applicability in sustainable energy conversion.