Multi-Ni@Ni phyllosilicate hollow sphere for CO2 reforming of CH4: influence of Ni precursors on structure, sintering, and carbon resistance
Multi-Ni@Ni phyllosilicate hollow spheres (NiPhy HS) were synthesized using different Ni precursors via hydrothermal and H2 reduction methods. Precursor effects to the NiPhy HS structure and catalytic performance for CO2 (dry) reforming of the CH4 (DRM) reaction were investigated and established. Ni@NiPhy-(Ac)2 achieved near equilibrium conversions with negligible carbon formation for the DRM reaction at 700 °C. The structure of NiPhy HS was influenced by different nickel precursors because Ni ions with different sizes were produced leading to their relatively different diffusion speeds through the previously formed NiPhy layer to further react with the silicate ions near the unreacted silica surface in the core part to form the new NiPhy phases. The unique pore structure with smallest pore size and pore volume for NiPhy-(Ac)2 compared with NiPhy-OAc and NiPhy-NO3 contributes to eliminating the deposition of carbon species due to the confinement effect. In addition, the strongest interaction between Ni and NiPhy phases for NiPhy-(Ac)2 inhibits the sintering of Ni nanoparticles and prevents the lifting away of Ni from NiPhy phases by the deposited carbon species thereby retarding the growth of carbon nanotubes. This study demonstrates a method to design other metal (M = Co, Fe, and Cu) phyllosilicate nano-hollow spheres with high metal loading as high sintering and carbon resistant catalysts for other catalytic applications.