Probing the enhanced catalytic activity of carbon nanotube supported Ni-LaO hybrids for the CO reduction reaction.

Oxygenated functionalized carbon nanotube (oCNT) supported LaO-promoted Ni nanoparticles (10Ni-xLa/oCNT) were prepared by the co-impregnation method and tested for synthetic natural gas from the CO reduction reaction. Several advanced characterization methods, including atomic resolution scanning transmission electron microscopy (STEM), temperature programmed experiments (TPSR, CO-TPD, and H-TPR) and X-ray photoelectron spectroscopy (XPS), were applied to explore, for the first time, the origin of structure modulation of LaO species on oCNT supported Ni-LaO hybrids and the structure-activity relationship over the CO reduction reaction. The Z-contrast STEM-HAADF results revealed that the LaO 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 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 modulation catalyst with 2 wt% of La metal loading not only presented low CO activation temperature at only 163 °C, but also resulted in extremely high CH selectivity (100%) compared with the initial supported Ni catalyst (52.7% of CH selectivity at 300 °C).