Catalytic performance of Ni/CeO<inf>2</inf> catalysts prepared from different routes for CO<inf>2</inf> methanation

Abstract

In thid study, Ni/CeO2 catalysts were prepared by a one-step co-precipitation of nickel and cerium salts in a NaOH solution treated by different heating methods including microwave (MW), hydrothermal (HM) and evaporation (EP). With TEM observation, the co-precipitation provided the catalysts containing a highly crystalline CeO2 of a (111) plane structure with d-spacing of 3.15–3.24 Å. The obtained CeO2 nanoparticles exhibited a pseudo-spherical shape with a size range of 10.8–12.1 nm. Based on HR-TEM analyses, NiO nanoparticles with a large size range of 48.8–51.2 nm were found to be incorporated within the CeO2 nanostructure. By N2 sorption measurement, all Ni/CeO2 catalysts possessed a mesoporous characteristic with a specific surface area range of 70.5–75.7 m2/g and an average pore diameter of 30 nm. XRD results revealed that NiO species could be completely transformed into Ni0 species by the H2 reduction process. XPS analyses further confirmed the presence of Ni0 species with a prominent peak at an energy bandgap of 852.6 eV. Hydrogen temperature-programmed reduction (H2-TPR) confirmed that α and β peaks of NiO species were completely reduced at a temperature lower than 500 °C. The Ni/CeO2 catalyst prepared by MW method exhibited a higher strong metal-support interaction (SMSI) between Ni and CeO2 revealed by H2 consumption results. The Ni/CeO2 catalysts prepared by MW, HM, EP methods exhibited the CO2 methanation activity with TOF of 13.6, 10.8 and 5.8 s−1, which could be correlated with the Ni crystallite sizes of 42.2, 50.5 and 52.8 nm, respectively. All prepared Ni/CeO2 catalysts exhibited the stable catalytic performances with a negligible drop in CO2 conversion and CH4 selectivity over 72 h-time-on-stream test. In comparison, the MW method with a rapid and uniform heating under autogenous pressure could result in the Ni/CeO2 catalyst with the superior catalytic activities due to the higher dispersion of Ni.