The prevalence of surface oxygen vacancies over the mobility of bulk oxygen in nanostructured ceria for the total toluene oxidation

Jose Manuel López,Alexander L Gilbank,Tomás García,Benjamín Solsona,Said Agouram,Laura Torrente-Murciano

doi:10.1016/j.apcatb.2015.03.017

Abstract

This paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria. A series of nanostructured rods and cubes with different physico–chemical properties have been synthesized, characterized and tested in the total toluene oxidation. The variation of the temperature and base concentration during the hydrothermal syntheses of nanostructured ceria leads not only to different ceria morphologies with high shape purity, but also to structures with tuneable surface areas and defect concentrations. Ceria nanorods present a higher surface area and a higher concentration of bulk and surface defects than nanocubes associated with their exposed crystal planes, leading to high oxidation activities. However, for a given morphology, the catalytic activity for toluene oxidation is directly related to the concentration of surface oxygen defects and not the overall concentration of oxygen vacancies as previously believed.

Highlights

Ceria-based materials have been intensively studied in the catalysis field, either as pure dioxide (CeO2) or doped materials, due to its high abundance and desirable combination of chemical and physical properties [1,2]
This paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria
We show that crystallite size plays a key role in the reactivity of ceria rods with enclosing (1 1 0) and (1 0 0) facets, while it has the modest effect on the catalytic activity of ceria cubes with exposed (1 0 0) facets

Summary

Introduction

Ceria-based materials have been intensively studied in the catalysis field, either as pure dioxide (CeO2) or doped materials, due to its high abundance and desirable combination of chemical and physical properties [1,2]. Despite the importance of morphology in the final chemical and physical properties of ceria, particle and crystallite size are believed to play a key role, especially determining its catalytic activity. This role is still not fully understood leading to the current debate in the literature. It is important to highlight that particle size does not seem to be directly related to reducibility in zirconium-doped ceria [15] Most of these studies refer to particulated ceria and there is still a lack of understanding of the relative dependency of crystallite size and surface and bulk properties to catalytic activity of different ceria morphologies in which different surface planes are selectively exposed. Bulk oxygen defects is not directly related to the resulting catalytic activity

Synthesis and characterization of nanostructured ceria

Results and discussion

Toluene oxidation reactions

Conclusions