Effect of catalytic site position: Nickel nanocatalyst selectively loaded inside or outside carbon nanotubes for methane dry reforming

The catalysts with nickel nanoparticles selectively loaded inside or outside carbon nanotubes (CNTs) were prepared via wet chemical method to study the different catalytic site position effect such as inside and outside CNTs. The catalysts were characterized by N2 adsorption, transmission electron micrographs (TEM), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. TEM images and XPS demonstrated that most of nickel nanoparticles were controlled to be loaded at interior or exterior surface of CNTs. The H2-TPR analysis results showed that the nickel oxide at the inside of the CNTs was easier to be reduced by H2, which was attributed to the confinement effect of CNTs. Furthermore, this different reducibility resulted in an obvious different catalytic performance in terms of methane reforming of carbon dioxide. The reaction results demonstrated that the nickel catalyst with the nanoparticles inside CNTs exhibited higher catalytic activity and stability compared with the catalyst where nickel nanoparticles loaded outside CNTs.