Ultrasmall Ni Nanoclusters on Perovskites: Highly Stable and Coke-Resistant Catalysts for Methane Reforming with CO₂

Catalytic dry reforming of methane (DRM) offers a sustainable route for converting greenhouse gases (CH₄ and CO₂) into syngas, yet suffers from rapid catalyst deactivation due to coke formation. Here, we report a rational approach to control Ni nanostructure and interface properties by tuning the reduction temperature of Ni-substituted La₂Ti₂O₇ perovskite catalysts. Catalysts reduced at 800 °C formed ultrasmall, fully exposed Ni nanoclusters with a Ni-Ni coordination number of ∼3. These clusters were strongly anchored to oxygen-deficient perovskite surfaces, enabling efficient CH₄ activation while suppressing carbon accumulation. In contrast, high-temperature (900 °C) reduction induced Ni sintering, loss of surface reactivity, and increased coke formation, whereas low-temperature (600 and 700 °C)-reduced catalysts exhibited negligible activity. Mechanistic studies using CO adsorption FT-IR, CO₂-TPD, in situ DRIFTS, and XPS revealed that DRM over the highly active catalyst proceeds via a cooperative mechanism, in which CH₄ activation occurs at Ni sites while CO₂ is primarily activated on the La₂Ti₂O₇ support.