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Mechanism and selectivity of MOF-supported Cu single-atom catalysts for preferential CO oxidation.
- Source :
- Journal of Materials Chemistry A; 2/7/2024, Vol. 12 Issue 3, p3084-3095, 12p
- Publication Year :
- 2024
-
Abstract
- Zr-based UiO-66 metal–organic frameworks are ideal platforms for the design and development of heterogeneous single-atom catalysts (SACs) because of their thermal and chemical stability with the presence of structural defects, enabling the introduction of isolated metal atoms. Elucidating the structure–reactivity relationships and understanding reaction mechanisms for these catalysts are crucial for their industrial applications. We focus here on these aspects for a technically important reaction, preferential CO oxidation (PROX) on a UiO-66-supported Cu SAC by following temperature perturbations in catalytic performance in correlation with changes in the electronic and adsorption properties, which are validated by comprehensive DFT computations. In situ DR-UV-VIS, XANES and NAP-XPS measurements indicated an increase of Cu<superscript>1+</superscript>-like states and partial reduction of ZrO<subscript>x</subscript> nodes with the increase in reaction temperature, which correlated with a decrease in PROX selectivity. Under similar conditions, DRIFTS measurements revealed a decay of CO<subscript>ad</subscript> adsorption on Cu (i.e., CO<subscript>ad</subscript>@Cu<superscript>1+</superscript> species) and a corresponding red-shift under PROX conditions compared to CO oxidation, suggesting reduction-mediated charge transfer at the Cu–ZrO<subscript>x</subscript> interface. In contrast to the CO oxidation cycle which commences by CO adsorption on Cu<superscript>1+</superscript>-like sites, DFT computations revealed that the H<subscript>2</subscript> oxidation cycle starts with the reaction of H<subscript>2</subscript> with a pre-adsorbed O<subscript>2</subscript> molecule on Cu<superscript>1+</superscript>-like sites, resulting in the generation of a H<subscript>2</subscript>O molecule and Cu<superscript>2+</superscript>-like sites, which are subsequently reduced to Cu<superscript>1+</superscript>-like sites through a successive reaction with a second H<subscript>2</subscript> (or CO) molecule. Adsorption configurations and energies of CO and H<subscript>2</subscript>O co-adsorption indicated a competitive adsorption phenomenon on Cu species, which depends on the oxidation state of the Cu ion with a preference for CO adsorption on Cu<superscript>1+</superscript>-like sites, while H<subscript>2</subscript>O exhibits a stronger affinity for Cu<superscript>2+</superscript>-like sites. These results are discussed in terms of the reaction mechanism and PROX selectivity in Cu SAC catalysts and present a model for understanding the catalytic phenomena on MOF-supported SACs. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 20507488
- Volume :
- 12
- Issue :
- 3
- Database :
- Complementary Index
- Journal :
- Journal of Materials Chemistry A
- Publication Type :
- Academic Journal
- Accession number :
- 175142181
- Full Text :
- https://doi.org/10.1039/d3ta05047e