Surface morphology and phase stability effect of Ceria-Hafnia (CHx) binary metal oxides on soot oxidation activity

Abstract

CeO<inf>2</inf>-HfO<inf>2</inf> (CH<inf>x</inf>) binary metal oxides over whole composition range (0–100%) are synthesised using the EDTA-Citrate method and calcined at 600 °C/5 h. From XRD analysis, the sample series are classified as fluorite (F) phase for CH10-CH30, hybrid (F + M) phase for CH40-CH90 and monoclinic (M) phase for CH100 sample, respectively and the results were further confirmed using Raman spectroscopy. From SEM analysis, a clear surface morphology change is noticed for fluorite, hybrid and monoclinic phases of the CH<inf>x</inf> binary metal oxides. Further, Selected Area Electron Diffraction (SAED) analysis also confirmed the single and hybrid phases of CH<inf>x</inf> binary metal oxides. The soot oxidation for the CH<inf>x</inf> binary metal oxides displayed high catalytic activity for Fluorite phase (CH10 ? CH30) samples and a decrease in catalytic activity is noticed for the Hybrid phase (CH40 ? CH90) samples. The change in catalytic activity coincides with the change in the surface morphology and phase change for the CH<inf>x</inf> binary metal oxides. Among the Fluorite phase samples, CH10 sample displayed the highest catalytic activity (T<inf>50</inf> = 430 °C) with higher surface area (29 m2/g), lower particle size (26 nm), lower degree of agglomeration (? = 2.8) higher surface oxygen concentration (44%). Isothermal-Time-on-stream (ITOS) analysis also showed that the CH10 sample can achieve T<inf>50</inf> in a shorter time than compared to other CH<inf>x</inf> binary metal oxides. Surface morphology and phase stability can also play as key descriptors in screening CH<inf>x</inf> binary metal oxides for soot oxidation activity. © 2018 Elsevier B.V.