The synergistic interaction between oxygen vacancies in Ni single atoms/TiO₂ support and adjacent NiO nanoparticles boosts the CO₂ methanation process.

Abstract

Integrating multiple active sites within a single catalytic system has emerged as a promising strategy to unlock new performance windows in heterogeneous catalysis. Herein, we report a novel design configuration of a heterogeneous catalyst co-loaded with Ni single atoms and NiO nanoparticles on the oxygen-deficient TiO₂ support, denoted as Ni-SA+NP, for highly efficient CO₂ methanation. This tandem system achieves an unprecedented CH₄ production yield of ∼4,658 µmol g⁻¹ at 573 K with a CH₄ production rate of ∼16768 mmol g⁻¹ h⁻¹ and CH₄ selectivity of 90%, significantly surpassing the performance of catalysts containing only Ni single atoms (∼2,794 µmol g⁻¹ at 573 K) and NiO nanoparticles (∼4,018 µmol g⁻¹ at 573 K). While Ni single atoms offer excellent atomic dispersion and strong metal-support interaction, they often suffer from oxidation and a lack of ensemble sites, which limits multistep reaction kinetics. Our strategy addresses these limitations by creating oxygen vacancies in oxidized Ni single atoms and providing ensemble sites (adjacent NiO nanoparticles and oxygen-deficient TiO₂ support), thereby enabling a synergistic interaction between oxygen vacancies in Ni single atoms/TiO₂ support and adjacent NiO nanoparticles. The results of in situ X-ray absorption spectroscopy reveal that the oxygen vacancies in Ni single atoms and TiO₂ support facilitate the CO₂ activation, whereas the adjacent NiO nanoparticles interacts with H₂ molecules (Ni-O^ads + H₂ → Ni + H₂O) and undergo reduction to metallic Ni during CO₂ methanation. This multiple-site architecture creates a highly active interface for CO₂ activation and hydrogenation, setting a new benchmark for methanation catalysis and providing a scalable blueprint for hybrid single-atom/nanoparticle catalyst design.