Magnetic Properties of Efficient Catalysts Based on La-Doped Ceria-Supported Nickel Nanoparticles for rWGS Reaction. Influence of Ni Loading

Abstract

The influence of Ni loading on Ce0.9La0.1O1.95-supported Ni catalysts for CO2 reduction with hydrogen (reverse water gas shift reaction) is studied. The samples are prepared by solution combustion synthesis (SCS), leading to materials with high thermal resistance, purity, and crystallinity, consisting of metallic nickel nanoparticles supported on La-doped ceria. The study of the ferromagnetic Curie temperature (TC) and magnetization cycles suggest that the Ni nanoparticles are superparamagnetic, exhibiting magnetic order at room temperature, with TC strongly dependent on the particle size; this spans from 1.9, up to 80 nm. The structural study from synchrotron X-ray diffraction data and Raman spectroscopy clearly show the presence of oxygen vacancies in the fluorite crystal structure of the Ce0.9La0.1O2−δ matrix, which increase in the spent catalysts by forming a greater proportion of Ce3+ compared with their fresh counterparts. This is confirmed from the Raman spectra, showing an increase in the relative intensity of the band placed between 520 and 610 cm−1. All the catalysts show very high reaction rate per unit mass of catalyst; the CO2 conversion after 6 h for the catalyst with 10% Ni molar (Ni0.1/Ce0.9La0.1) is 57% (2.4 moles CO·h−1·g catalyst−1), very close to the thermodynamic equilibrium (59.3%).