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.
Highlights
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
We focus on the use of near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the surface and subsurface arrangements in ceria-based catalysts
Combined with in situ XAFS analysis, the results revealed the transformation of dispersed Rhδ+ species and small CrOx nanoparticles supported on CeO2 to Rh nanoclusters, Cr(OH)3 species and CeO2−x when treated with H2
Summary
Ceria-based catalysts have been widely investigated in the last decades for different applications. Ceria displays an extraordinary oxygen storage capacity (OSC) and redox properties because it has the ability to accommodate a large number of oxygen vacancies under a slightly reducing atmosphere to give under-stoichiometric CeO2−x , which can be oxidised back to CeO2 in an oxygen-containing atmosphere This occurs without structural modification of the fluorite ceria lattice and is not limited to the surface, and takes place in the bulk [7,8]. We focus on the use of near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the surface and subsurface arrangements in ceria-based catalysts Their dynamic behaviour under operation conditions to obtain structure-activity relationships will be revised
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