Probing the enhanced catalytic activity of carbon nanotube supported Ni-LaOx hybrids for the CO2 reduction reaction

Abstract

Oxygenated functionalized carbon nanotube (oCNT) supported LaO_x-promoted Ni nanoparticles (10Ni-xLa/oCNT) were prepared by the co-impregnation method and tested for synthetic natural gas from the CO₂ reduction reaction. Several advanced characterization methods, including atomic resolution scanning transmission electron microscopy (STEM), temperature programmed experiments (TPSR, CO₂-TPD, and H₂-TPR) and X-ray photoelectron spectroscopy (XPS), were applied to explore, for the first time, the origin of structure modulation of LaO_x species on oCNT supported Ni-LaO_x hybrids and the structure–activity relationship over the CO₂ reduction reaction. The Z-contrast STEM-HAADF results revealed that the LaO_x species are mostly in the size of the sub-nano scale and highly dispersed on the surface of Ni nanoparticles and oCNT, and consequently no diffraction peak of LaO_x was observed from XRD results. TEM analysis showed that the Ni nanoparticle sizes were similar among all samples either after reduction or after reaction due to the relatively strong interaction between Ni and oxygenated groups on CNT supports, regardless of the influence of the La mass loading. It was suggested that the catalytic performance trend was due to the structural variation rather than the size effect. The LaO_x modulation catalyst with 2 wt% of La metal loading not only presented low CO₂ activation temperature at only 163 °C, but also resulted in extremely high CH₄ selectivity (100%) compared with the initial supported Ni catalyst (52.7% of CH₄ selectivity at 300 °C).