Calcination-Induced Pore Evolution in TiO₂ Supports Governing Ni Accessibility for Dry Methane Reforming

The influence of support calcination temperature on pore evolution, nickel (Ni) accessibility, and catalytic behavior was investigated using Ni-loaded titanium dioxide (TiO₂) catalysts for the dry reforming of methane (DRM). The TiO₂ supports calcined between 400°C and 1200°C showed a structural transition from a hierarchical mesoporous-macroporous framework to predominantly macroporous and eventually plate-like morphologies. Despite similar Ni loading (1.1-1.2 wt%), reducibility, and Ni particle size (∼60-86 nm), the accessibility of Ni sites varied significantly due to calcination-induced structural evolution. Notably, the most active catalyst, Ni/TiO₂-HR-C12, achieved a high initial CH₄ conversion of ∼93% and an H₂/CO ratio of ∼0.95 at 800°C. It also exhibited superior stability during 50 h at 700°C. Low-temperature-calcined support allowed Ni precursors to infiltrate mesopores, which collapsed during subsequent 900°C calcination, leading to Ni encapsulation and poor activity. In contrast, high-temperature-calcined supports (≥900°C) generated thermally stable structures that prevented Ni infiltration, preserving surface-exposed Ni sites. This high site accessibility is a decisive factor governing the enhanced DRM performance. These findings demonstrate that support thermal stability and Ni accessibility outweigh mesoporosity or Ni particle size, offering insights for designing thermally robust oxide-supported catalysts.