Properties of small sized confined nickel nanoparticles over silica for CO2 methanation

The catalytic activity of Ni based catalysts for CO 2 methanation reaction is directed by the size and dispersion of Ni nanoparticles (NPs). In this study, a series of materials containing 10 wt.% Ni supported in SBA-15 silica were prepared with the NPs of sizes ranging from 3 nm to 9 nm by an optimized Melt Infiltration approach (MIA) or Incipient Wetness Impregnation (IWI) method. For reference, 12 nm NPs supported on commercial silica prepared by the classical impregnation method (IMP). Various techniques, such as X-ray powder diffraction (XRD), N 2 physisorption, S/TEM- coupled with EDX mapping, H 2 temperature programmed reduction (H 2 -TPR), H 2 -chemisoprtion, X-ray photoelectron spectroscopy (XPS), were used to characterize the calcined and H 2 reduced catalysts. It was found that the 3 nm metallic Ni nanoparticles in Ni/MIA catalyst could be stabilized dispersed in the secondary intra-wall porosity of SBA-15 with long mesoporous channels. Whereas, 9 nm metallic Ni nanoparticles in Ni/IWI catalyst situated in the main mesoporous channels of SBA-15. The catalytic performance of the aforementioned catalysts towards CO 2 methanation was evaluated at various temperatures. The Ni/MIA catalyst exhibits 84% CO 2 conversion and a 98% CH 4 selectivity at 360 °C, and no significant decline of CO 2 conversion is noticed even after 70 h of continuous reaction. CO 2 methanation activity obtained at the different Ni particle sizes, at 360 °C, is discussed along with proportion of face/edge/corner active surface sites determined by geometric model. It was shown that the activity of Ni/MIA catalyst is associated to the face atoms, however for Ni/IWI catalyst, activity corresponded to the combination of corner and edge atom sites. Herein, the melt infiltration-assisted strategy on SBA-15 silica provides an effective methodology to stabilize small nanoparticles sized and confined Ni catalysts efficient and stable for CO 2 methanation.