This work examines how the size of nickel particles impacts CH4 reforming with CO2 over Ni/γ-Al2O3 catalysts aimed at syngas production. A set of catalysts containing Ni loadings from 5 to 20 wt% (with particle sizes between 3.5 and 10.5 nm) was prepared and tested at CO2/CH4 = 1, GHSV = 60 L/(gcat·h), 700–800°C, and 1 bar. Increasing the Ni loading enhanced CH4 conversion from 38.6% (Ni5, 700°C) to 70.2% (Ni20, 800°C) and CO2 conversion from 45.4% to 85.6%. However, turnover frequency (TOF) decreased from 1.23 to 0.90 s-1 by increasing the Ni particle size, which indicates a structure-sensitive reaction. The H2/CO ratio stayed under one (0.899–0.919) because of the reverse water-gas shift (RWGS) reaction, while coke formation increased from 0.037 to 0.083 μmol/(gcat·min). The experimental data were well captured by a size-dependent kinetic model derived from the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism, achieving a mean absolute relative residual under 3%. The size-independent activation energy (Eₐ∞) for CH4 reforming with CO2 was determined as 86.1 kJ/mol. These results highlight the role of Ni particle size in regulating the activity, selectivity, and carbon deposition behavior in the CO2 reforming of CH4.

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