Investigation of the Thermodynamic Properties of Surface Ceria and Ceria–Zirconia Solid Solution Films Prepared by Atomic Layer Deposition on Al2O3

Tzia Onn,Cong Wang,Xinyu Mao,Raymond Gorte,Chao Lin

doi:10.3390/inorganics5040069

Abstract

The properties of 20 wt % CeO2 and 21 wt % Ce0.5Zr0.5O2 films, deposited onto a γ-Al2O3 by Atomic Layer Deposition (ALD), were compared to bulk Ce0.5Zr0.5O2 and γ-Al2O3-supported samples on which 20 wt % CeO2 or 21 wt % CeO2–ZrO2 were deposited by impregnation. Following calcination to 1073 K, the ALD-prepared catalysts showed much lower XRD peak intensities, implying that these samples existed as thin films, rather than larger crystallites. Following the addition of 1 wt % Pd to each of the supports, the ALD-prepared samples exhibited much higher rates for CO oxidation due to better interfacial contact between the Pd and ceria-containing phases. The redox properties of the ALD samples and bulk Ce0.5Zr0.5O2 were measured by determining the oxidation state of the ceria as a function of the H2:H2O ratio using flow titration and coulometric titration. The 20 wt % CeO2 ALD film exhibited similar thermodynamics to that measured previously for a sample prepared by impregnation. However, the sample with 21 wt % Ce0.5Zr0.5O2 on γ-Al2O3 reduced at a much higher P O 2 and showed evidence for transition between the Ce0.5Zr0.5O2 and Ce0.5Zr0.5O1.75 phases.

Highlights

Ceria is a component in a number of commercial catalysts, as demonstrated in a recent, comprehensive review [1]
This loss in reducibility is accompanied by a loss in surface area, it is not a kinetic phenomenon, since the ceria–zirconia solid solutions that are used in three-way catalysts have low surface areas but still maintain their Oxygen-Storage Capacitors (OSC) properties [20]
While the loss in surface area does not prevent the application of ceria–zirconia solid solutions for OSC, high surface areas are required in other cases

Summary

Introduction

Ceria is a component in a number of commercial catalysts, as demonstrated in a recent, comprehensive review [1]. It is known that pure ceria becomes essentially unreducible after harsh redox cycling [19] This loss in reducibility is accompanied by a loss in surface area, it is not a kinetic phenomenon, since the ceria–zirconia solid solutions that are used in three-way catalysts have low surface areas but still maintain their OSC properties [20]. For CO-oxidation and WGS reactions over Pd/ceria, the sites at the Pd–ceria boundary have been shown to exhibit much higher rates [21]. In these examples, the surface area of the ceria should be as high as possible

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Results

Conclusion