Abstract
Nickel (Ni) phyllosilicate-derived catalysts have recently gained attention for the CO(2) 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 Ni(2+). 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, Ni(3)Si(2)O(5)(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 Ni(2+)) limiting the carbon formation via CO disproportionation (2CO ⇌ C((s)) + CO(2)) on the KIT-6-templated silica. This study provides valuable insights into the design of more stable methane reforming catalysts.