Catalytic Mechanisms in Preferential Oxidation Reactions

Preferential oxidation reactions (PROX) serve a central role in the purification of hydrogen streams by selectively oxidising trace carbon monoxide to carbon dioxide in the presence of excess hydrogen. The underlying catalytic mechanisms typically involve redox cycling between reduced and oxidised states of active metal species, often supported on oxide materials that supply labile oxygen. In copper–ceria systems, for example, CO adsorption and activation occur at metallic copper sites, while ceria provides facile oxygen storage and release through its variable oxidation states. The interplay between metal dispersion, support morphology and oxygen vacancy concentration dictates both activity and selectivity. Recent advances have revealed that isolated metal atoms anchored on mixed oxide supports can achieve high selectivity by minimising undesired hydrogen oxidation. Operando spectroscopic studies have highlighted the dynamic evolution of surface intermediates and the importance of tuning metal–support interactions to stabilise reactive oxygen species. Alternative catalysts based on spinel or mineral oxides leverage lattice oxygen, with dopants such as manganese or tin modifying redox properties and enhancing stability in the presence of moisture and carbon dioxide. Mechanistic models, supported by density functional theory and transient kinetic experiments, have converged on a dual-site framework in which CO and O2 activation occur at distinct but cooperative sites. Such insights guide the rational design of catalysts capable of delivering high CO conversion at low temperatures while suppressing hydrogen loss, thus facilitating the deployment of proton exchange membrane fuel cells and other hydrogen technologies on a global scale.

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Catalytic Mechanisms in Preferential Oxidation Reactions publication trend

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Technical terms

Preferential oxidation (PROX): selective catalytic oxidation of a minor component (e.g. CO) in the presence of a major reactant (e.g. H₂).

Oxygen vacancy: defect site in an oxide lattice where an oxygen atom is missing, facilitating oxygen mobility and redox activity.

Single‐atom catalyst (SAC): catalyst in which isolated metal atoms are dispersed on a support, maximising atomic efficiency and selectivity.

Operando spectroscopy: in situ analytical technique that monitors catalyst structure and intermediates under actual reaction conditions.

Redox cycling: reversible transformation between reduced and oxidised states of catalytic species, essential for sustained activity.

References

1. Kinetic and Computational Studies of CO Oxidation and PROX on Cu/CeO2 Nanospheres. Topics in Catalysis (2023).
2. Mineral Manganese Oxides as Oxidation Catalysts: Capabilities in the CO-PROX Reaction. ACS Sustainable Chemistry & Engineering (2021).
3. Preferential CO Oxidation on a Highly Active Cu Single Atom Catalyst Supported by Ce−TiOx. ChemCatChem (2022).