In Situ Insights into Ni Phyllosilicate Evolution: Cationic Ni Species as Key to Enhanced Stability in Methane-Rich...

Nickel (Ni) phyllosilicate-derived catalysts have recently gained attention for the CO₂ reforming of methane. However, understanding of the underlying reduction pathways and structural factors that determine stable catalytic performance is still missing. Herein, we developed a one-pot synthesis with ammonia solution to produce nickel catalysts supported on silica, utilizing a modified KIT-6 protocol. Under the proposed alkaline conditions (pH = 9), the silanol groups were deprotonated (Si-O^-) and the resulting negatively charged oxide surface could interact with Ni²⁺. This approach facilitated the in situ formation of Ni phyllosilicate within the silica framework, which contained isolated surface hydroxyl groups. In situ XAS-XRD revealed the presence of thermally stable crystalline Ni phyllosilicate, Ni₃Si₂O₅(OH)₄, with time-resolved XANES providing complementary insight into the redox transformation of nickel species associated with dehydroxylation. Partially unreduced nickel species retained a cationic state during the catalytic reaction at 700 °C, with a higher amount of nickel phyllosilicate observed after 50 h in contrast to the state after 1 h. On the whole, the one-pot synthesis produced small Ni crystallites with improved dispersion, both of which had a part in ensuring stable catalytic performance. We also uncovered the crucial role of ionic species (Ni⁺ and Ni²⁺) limiting the carbon formation via CO disproportionation (2CO ⇌ C_(s) + CO₂) on the KIT-6-templated silica. This study provides valuable insights into the design of more stable methane reforming catalysts.