From earth material to energy production: Ni-based modified halloysite catalysts for CO₂ methanation

In present study, halloysite (Hal) clay mineral was modified by promoters, such as ceria, Cu-doped and La-doped ceria. Comprehensive techniques were used to study the microstructure, the surface coordination environment, redox behavior and acid/base properties; the interaction between Ni⁰ nanoparticles and interfacial sites was unveiled. TEM demonstrates that the Hal layer modification promotes high dispersion of Ni⁰ nanoparticles with predominant Ni⁰ (111) facets. Particularly, Hal modification with Ce and La reduces Ni particles size (∼9 nm). XPS reveals the co-presence of Ce^III and Ce^IV species on the surface, which plays a crucial role in facilitating the CO₂ activation. Moreover, XAS studies provide insights into the structural properties and surface interactions at unit cell scale length. Ni/10La10CeHal catalyst exhibits higher oxidation resistance compared to Ni/Hal. In particular, the Ni/10La10CeHal catalyst exhibits the highest CO₂ conversion (X_CO2 = 67%) amongst the studied catalysts, with a Y_CH4 of approximately 61% and a S_CH4 of 91% at 450°C. Whereas the catalyst's Y_CO and S_CO are only ∼6% and ∼9%, respectively, at 450°C compared to both Ni/5Cu15CeHal and Ni/10Cu10CeHal. The Ni/10La10CeHal catalyst showed a steady catalytic performance over 50 h maintaining a X_CO2 of 65% at 450°C, attributed to its extrinsic features.