Unveiling the Origin of Structure Sensitivity for CO ₂ Methanation over Ni/CeO ₂ Catalysts

In the design of efficient heterogeneous catalysts, a high dispersion of the metal active phase on oxide supports is crucial. Reducing the metal particle size to expose more active sites helps to improve mass-specific activity. However, many industrial catalytic processes suffer from structure-sensitive issues. When the metal particle size is reduced to a certain extent, the turnover frequency (TOF) of CO2 conversion can significantly decrease, leading to a reduction in mass-specific activity, along with an impact on product selectivity. A typical example is the low TOF and high CO selectivity of small Ni particles in CO2 methanation. Herein, we demonstrate that both the intrinsic activity (TOF) and CO/CH4 selectivity in CO2 methanation are highly sensitive to the Ni particle size over Ni/CeO2 catalysts and reveal the structure sensitivity mechanism, providing a reference for optimizing performance in structure-sensitive reactions. Ni(10.6)/CeO2 exhibited optimal performance with a high CH4 formation rate of 6.38 mol gNi–1 h–1 and nearly 100% CH4 selectivity at 300 °C. According to mechanistic studies, the variation in Ni particle size regulated the adsorption of CO* intermediates on the catalyst surface and thus determined CO/CH4 product distribution. Meanwhile, catalysts with smaller and larger Ni particles followed the formate-mediated CO pathway and the CO2 direct dissociation pathway, respectively. In contrast, catalysts with medium-sized Ni particles followed a dual pathway, affording high intrinsic activity of the CO2 methanation intrinsic activity.