Catalytic performance of Ni/CeO2 catalysts prepared from different routes for CO2 methanation

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 angstrom. 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 N-2 sorption measurement, all Ni/CeO2 catalysts possessed a mesoporous characteristic with a specific surface area range of 70.5-75.7 m(2)/g and an average pore diameter of 30 nm. XRD results revealed that NiO species could be completely transformed into Ni-0 species by the H-2 reduction process. XPS analyses further confirmed the presence of Ni-0 species with a prominent peak at an energy bandgap of 852.6 eV. Hydrogen temperature-programmed reduction (H-2-TPR) confirmed that alpha and beta peaks of NiO species were completely reduced at a temperature lower than 500 degrees C. The Ni/CeO2 catalyst prepared by MW method exhibited a higher strong metal-support interaction (SMSI) between Ni and CeO2 revealed by H-2 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. (C) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.