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 CeIII and CeIV 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 (XCO2 = 67%) amongst the studied catalysts, with a YCH4 of approximately 61% and a SCH4 of 91% at 450°C. Whereas the catalyst's YCO and SCO 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 XCO2 of 65% at 450°C, attributed to its extrinsic features.