Effects of catalyst morphology on oxygen defects at Ni–CeO2 interfaces for CO2 methanation

Abstract

Oxygen defects in Ni–CeO₂ catalysts play an important role in CO₂ methanation. Herein, efforts are centered on enhancing the concentration of oxygen defects by tuning the Ni–CeO₂ catalyst morphology to enhance methane productivity. A relationship between oxygen defect concentration, the structure of Ni–CeO₂ catalysts and catalytic performance for CO₂ methanation is established through a combination of catalyst characterization (scanning transmission electron microscopy (STEM), temperature programmed reduction (H₂-TPR), H₂ pulse chemisorption, X-ray diffraction, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and Raman spectroscopy) and kinetic studies. Raman studies indicated that (i) inverse Ni–CeO₂ catalyst structures, along with (ii) incorporation of low amounts (<1 wt%) of aliovalent, rare-earth metal dopants, such as Pr, enhanced the formation of oxygen defects, consequently leading to high methane productivity. In situ DRIFTS studies showed that CO₂ methanation over Ni–CeO₂ inverse catalysts with the best catalytic performance followed a formate reaction pathway.