Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

Abstract

The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.

Low-Temperature Methane Partial Oxidation over Pd Supported on CeO2: Effect of the Preparation Method and Precursors

“…These differences demonstrate that the electronic state of palladium at the surface of the catalysts strongly depends on the preparation method. The shift to lower binding energy values in the samples prepared by mechanochemistry is indicative of surface oxidized Pd strongly interacting with ceria [30][31][32], which is in agreement with HRTEM and Raman spectroscopy data. In addition, the surface atomic ratio Pd 4+ /(Pd 4+ +Pd 2+ ) is much higher in the samples prepared by mechanochemistry and the values depend on the Pd precursor used; for the sample prepared by milling ceria and Pd acetate, this value is 0.6, which is much higher than the value recorded in the catalyst prepared by impregnation with Pd acetate (0.2).…”

Visible Emission on Nanostructured CeO2 Thin Films Obtained by Spray Pyrolysis

“…Deconvolution shows the presence of two multiplets (u y v), associated with the spin orbit splitting orbitals Ce 3d 3/2 and 3d 5/2 . [4,13,16,20,[26][27][28] Signals u 000 , v 000 , u 00 , v 00 , u, and v are associated with the state 3d 10 4f 0 of the 4þ oxidation state of cerium (Ce(IV)), while signals labeled as u 0 , v 0 , u 0 , and v 0 are associated with the state 3d 10 4f 1 of the 3 þ oxidation state of cerium (Ce(III)). [20,[26][27][28] The results of deconvolution are reported in Table 2.…”

“…[8][9][10][11][12] On the other hand, the capability of switching between Ce 3þ and Ce 4þ under oxidizing and reducing environments makes this material very attractive for technological applications in catalysis and photocatalysis. [6,[13][14][15][16] The use of nanostructured thin films increases the potential applications of this material. [11,17,18] CeO 2 thin films have been prepared by different physical and chemical methods, including flash evaporation, [19] electron-beam evaporation, [20][21][22] sputtering, [3,[23][24][25][26][27][28] laser ablation, [12,[29][30][31][32] and spray pyrolysis.…”

“…[ 8–12 ] On the other hand, the capability of switching between Ce 3+ and Ce 4+ under oxidizing and reducing environments makes this material very attractive for technological applications in catalysis and photocatalysis. [ 6,13–16 ]…”

Binder- free iridium based electrocatalysts: Facile preparation, high activity and outstanding stability for hydrogen evolution reaction in acidic medium

“…The use of ceria in catalysis relies on the beneficial effect of noble metal-ceria interactions [22]. In addition, the redox behavior of CeO 2 in which Ce 4+ and Ce 3+ can easily be formed under oxidizing and reducing conditions can enhance the efficiency of metal nanoparticles [23]. In fact, Ru x Ir y O 2 is such an example that CeO 2 enhanced the electrocatalytic activity when inserted into materials [24].…”