The surface of supported heterogeneous catalysts often contains adsorbed water and hydroxyl groups even when water is not directly added to the reaction stream. Nonetheless, the reactivity of adsorbed water and hydroxyl groups is rarely considered. We demonstrate that water and hydroxyl groups can not only directly participate in the catalytic oxidation processes but are also able to generate and stabilize the catalytically active metal-oxide interface. We show that the reduction of Pt-Fe-supported catalysts with hydrogen in the presence of adsorbed water or steam allows for achieving one of the highest preferential carbon monoxide oxidation activities at ambient temperature. These conditions create active iron-associated hydroxyl groups next to platinum nanoparticles with enhanced reactivity towards carbon monoxide oxidation. Density functional theory calculations suggest that hydroxylation of oxidic iron species stabilizes the FeOx(OH)y/Pt interface, via strong metal-support interaction, which is confirmed by chemisorption measurements. Kinetic experiments, including those with 18O-labeled water, in combination with operando infrared spectroscopy, show that water and hydroxyl groups directly participate in preferential carbon monoxide oxidation. A quantitative correlation between the catalytic activity of Pt-FeOx(OH)y/γ-Al2O3 catalysts and the Fe2+ concentration, obtained using operando X-ray absorption spectroscopy, shows that the number of active Fe2+ sites and the carbon monoxide oxidation rate per active site can be significantly increased by water-assisted pretreatment with hydrogen. This work provides a new example of positive role of strong metal-support interaction for the design of more active catalysts.@en

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper-exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X-ray powder diffraction with support from theory and other X-ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu-omega). This is the first comprehensive description of the structure of non-copper-oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion.@en

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper-exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X-ray powder diffraction with support from theory and other X-ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu-omega). This is the first comprehensive description of the structure of non-copper-oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion.@en

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper-exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X-ray powder diffraction with support from theory and other X-ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu-omega). This is the first comprehensive description of the structure of non-copper-oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion.@en

The direct conversion of methane to methanol using oxygen is a challenging but potentially rewarding pathway towards utilizing methane. By using a stepwise chemical looping approach, copper-exchanged zeolites can convert methane to methanol, but productivity is still too low for viable implementation. However, if the nature of the active site could be elucidated, that information could be used to design more effective catalysts. By employing anomalous X-ray powder diffraction with support from theory and other X-ray techniques, we have derived a quantitative and spatial description of the highly selective, active copper sites in zeolite omega (Cu-omega). This is the first comprehensive description of the structure of non-copper-oxo active species and will provide a pivotal model for future development for materials for methane to methanol conversion.@en

In this critical review we examine the current state of our knowledge in respect of the nature of the active sites in copper containing zeolites for the selective conversion of methane to methanol. We consider the varied experimental evidence arising from the application of X-ray diffraction, and vibrational, electronic, and X-ray spectroscopies that exist, along with the results of theory. We aim to establish both what is known regarding these elusive materials and how they function, and also where gaps in our knowledge still exist, and offer suggestions and strategies as to how these might be closed such that the rational design of more effective and efficient materials of this type for the selective conversion of methane might proceed further.@en

The metal-support interaction plays a critical role in heterogeneous catalysis. Under reducing conditions, oxidic supports may interact with supported metal particles, by either forming an oxide overlayer or an alloy. The structure of both the support and the nanoparticle, as well as of the interface itself, changes in response to varying environmental conditions. Here, we present a fullyab initioapproach to predict the structures and energetics of such systems for a range of transition metals (Me = Cu, Ru, Pd, Ag, Rh, Os, Ir, Pt, Au) supported on titania surfaces as a function of gas atmosphere composition. The competing formation of a monolayer comprising fully oxidized titania (TiO2), its reduced forms (Ti2O3, TiO), and the Ti-Me surface alloy, is investigated. The stability of each of these phases is found to be very sensitive to the environmental conditions and the supported metal. Encapsulation of metal, also known as classical strong metal-support interaction (SMSI), was predicted by thermodynamic driving force analysis. We show that a simple parameter, the Ti-Me alloy formation energy, is a good descriptor for the strength of the interaction between metal substrates and reduced titania monolayers and has predictive power towards the conditions under which an overlayer is stable. The presented thermochemical data and phase diagram analysis can be used to identify the structure and stability of supported metal catalysts under realistic conditions.@en

Ostwald ripening is a leading cause of the degradation of platinum group catalysts at high temperature in an oxidizing atmosphere. Recent experiments suggested that volatile species can be trapped on ceria, forming atomically dispersed active catalytic sites instead of large nanoparticles. Here we present a comparative density functional theory study of the interaction of PtO2(g), the most likely volatile species responsible for the process of Ostwald ripening, with various surfaces. Defect-free CeO2(111) and Al2O3(100) surfaces have a very small binding energy towards PtO2(g) compared to the platinum surface, indicative of particle growth. However, the stepped edge of the CeO2(111) surface effectively traps the mobile species, generating atomically dispersed catalysts. Such trapped single-atom platinum-on-ceria catalysts are predicted to have a square-planar [PtO4] structure, with the platinum atom strongly binding to the surface, preventing platinum atoms from aggregating into larger nanoparticles. These results provide an atomic insight into the single atom trapping and suggest a route for the development of sinter-resistant catalysts.@en

Ostwald ripening is a leading cause of the degradation of platinum group catalysts at high temperature in an oxidizing atmosphere. Recent experiments suggested that volatile species can be trapped on ceria, forming atomically dispersed active catalytic sites instead of large nanoparticles. Here we present a comparative density functional theory study of the interaction of PtO2(g), the most likely volatile species responsible for the process of Ostwald ripening, with various surfaces. Defect-free CeO2(111) and Al2O3(100) surfaces have a very small binding energy towards PtO2(g) compared to the platinum surface, indicative of particle growth. However, the stepped edge of the CeO2(111) surface effectively traps the mobile species, generating atomically dispersed catalysts. Such trapped single-atom platinum-on-ceria catalysts are predicted to have a square-planar [PtO4] structure, with the platinum atom strongly binding to the surface, preventing platinum atoms from aggregating into larger nanoparticles. These results provide an atomic insight into the single atom trapping and suggest a route for the development of sinter-resistant catalysts.@en

Ostwald ripening is a leading cause of the degradation of platinum group catalysts at high temperature in an oxidizing atmosphere. Recent experiments suggested that volatile species can be trapped on ceria, forming atomically dispersed active catalytic sites instead of large nanoparticles. Here we present a comparative density functional theory study of the interaction of PtO2(g), the most likely volatile species responsible for the process of Ostwald ripening, with various surfaces. Defect-free CeO2(111) and Al2O3(100) surfaces have a very small binding energy towards PtO2(g) compared to the platinum surface, indicative of particle growth. However, the stepped edge of the CeO2(111) surface effectively traps the mobile species, generating atomically dispersed catalysts. Such trapped single-atom platinum-on-ceria catalysts are predicted to have a square-planar [PtO4] structure, with the platinum atom strongly binding to the surface, preventing platinum atoms from aggregating into larger nanoparticles. These results provide an atomic insight into the single atom trapping and suggest a route for the development of sinter-resistant catalysts.@en

A detailed study on the synthesis of Pt3Co intermetallic nanoparticles supported on ceria via preferential chemical vapor deposition was conducted, leading to a fundamental understanding of the deposition process and the Co-Pt alloying. This understanding helps us to develop a facile and scalable method for preferential adding of a metal on the surface of another metal already supported on an oxide which facilitates the design of novel structured nanoparticles. The fluidized flow reactor eliminated the deposition profile and resulted in Pt3Co nanoparticles uniformly and homogeneously distributed on ceria. The kinetic study of cobalt deposition on the platinum surface, in accordance with DFT calculations, demonstrates that the platinum surface catalyzes the deposition reaction; while the ceria surface is inert in the preferential deposition temperature window between 150 °C and 180 °C. The obtained sample was characterized by in situ XRD, HAADF-STEM, FT-IR, and XAS methods. The results indicate the formation of uniform Pt3Co nanoparticles with an average size of 1.1 nm. This sample showed superior catalytic activity in preferential oxidation of CO with an almost twice higher CO conversion rate and CO2 selectivity compared to a classically synthesized sample with successive impregnation.@en

A detailed study on the synthesis of Pt3Co intermetallic nanoparticles supported on ceria via preferential chemical vapor deposition was conducted, leading to a fundamental understanding of the deposition process and the Co-Pt alloying. This understanding helps us to develop a facile and scalable method for preferential adding of a metal on the surface of another metal already supported on an oxide which facilitates the design of novel structured nanoparticles. The fluidized flow reactor eliminated the deposition profile and resulted in Pt3Co nanoparticles uniformly and homogeneously distributed on ceria. The kinetic study of cobalt deposition on the platinum surface, in accordance with DFT calculations, demonstrates that the platinum surface catalyzes the deposition reaction; while the ceria surface is inert in the preferential deposition temperature window between 150 °C and 180 °C. The obtained sample was characterized by in situ XRD, HAADF-STEM, FT-IR, and XAS methods. The results indicate the formation of uniform Pt3Co nanoparticles with an average size of 1.1 nm. This sample showed superior catalytic activity in preferential oxidation of CO with an almost twice higher CO conversion rate and CO2 selectivity compared to a classically synthesized sample with successive impregnation.@en

Through the combination of density functional theory calculations and ab initio atomistic thermodynamics modeling, we demonstrate that atomically dispersed platinum species on ceria can adopt a range of local coordination configurations and oxidation states that depend on the surface structure and environmental conditions. Unsaturated oxygen atoms on ceria surfaces play the leading role in stabilization of PtOx species. Any mono-dispersed Pt0 species are thermodynamically unstable compared to bulk platinum, and oxidation of Pt0 to Pt2+ or Pt4+ is necessary to stabilize mono-dispersed platinum atoms. Reduction to Pt0 leads to sintering. Both Pt2+ and Pt4+ prefer to form the square-planar [PtO4] configuration. The two most stable Pt2+ species on the (223) and (112) surfaces are thermodynamically favorable between 300 and 1200 K. The most stable Pt4+ species on the (100) surface tends to desorb from the surface as gas phase above 950 K. The resulting phase diagrams of the atomically dispersed platinum in PtOx clusters on various ceria surfaces under a range of experimentally relevant conditions can be used to predict dynamic restructuring of atomically dispersed platinum catalysts and design new catalysts with engineered properties.@en

Through the combination of density functional theory calculations and ab initio atomistic thermodynamics modeling, we demonstrate that atomically dispersed platinum species on ceria can adopt a range of local coordination configurations and oxidation states that depend on the surface structure and environmental conditions. Unsaturated oxygen atoms on ceria surfaces play the leading role in stabilization of PtOx species. Any mono-dispersed Pt0 species are thermodynamically unstable compared to bulk platinum, and oxidation of Pt0 to Pt2+ or Pt4+ is necessary to stabilize mono-dispersed platinum atoms. Reduction to Pt0 leads to sintering. Both Pt2+ and Pt4+ prefer to form the square-planar [PtO4] configuration. The two most stable Pt2+ species on the (223) and (112) surfaces are thermodynamically favorable between 300 and 1200 K. The most stable Pt4+ species on the (100) surface tends to desorb from the surface as gas phase above 950 K. The resulting phase diagrams of the atomically dispersed platinum in PtOx clusters on various ceria surfaces under a range of experimentally relevant conditions can be used to predict dynamic restructuring of atomically dispersed platinum catalysts and design new catalysts with engineered properties.@en

Through the combination of density functional theory calculations and ab initio atomistic thermodynamics modeling, we demonstrate that atomically dispersed platinum species on ceria can adopt a range of local coordination configurations and oxidation states that depend on the surface structure and environmental conditions. Unsaturated oxygen atoms on ceria surfaces play the leading role in stabilization of PtOx species. Any mono-dispersed Pt0 species are thermodynamically unstable compared to bulk platinum, and oxidation of Pt0 to Pt2+ or Pt4+ is necessary to stabilize mono-dispersed platinum atoms. Reduction to Pt0 leads to sintering. Both Pt2+ and Pt4+ prefer to form the square-planar [PtO4] configuration. The two most stable Pt2+ species on the (223) and (112) surfaces are thermodynamically favorable between 300 and 1200 K. The most stable Pt4+ species on the (100) surface tends to desorb from the surface as gas phase above 950 K. The resulting phase diagrams of the atomically dispersed platinum in PtOx clusters on various ceria surfaces under a range of experimentally relevant conditions can be used to predict dynamic restructuring of atomically dispersed platinum catalysts and design new catalysts with engineered properties.@en

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn-12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.@en

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn-12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.@en

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn-12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.@en

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn-12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.@en

Copper-containing zeolites exhibit high activity in the direct partial oxidation of methane into methanol at relatively low temperatures. Di- and tricopper species have been proposed as active catalytic sites, with recent experimental evidence also suggesting the possibility of the formation of larger copper oxide species. Using density functional theory based global geometry optimization, we were able to identify a general trend of the copper oxide cluster stability increasing with size. For instance, the identified ground-state structures of tetra- and pentamer copper clusters of CunOn2+ and CunOn-12+ stoichiometries embedded in an 8-ring channel of mordenite exhibit higher relative stability compared to smaller clusters. Moreover, the aluminium content and localization in the zeolite pore influence the cluster's stability and its geometrical motif, which offers a perspective of tuning the properties of copper-exchanged zeolites by creating copper oxide clusters of a given structure and size. With the activity of the cluster towards methane being connected to its stability, such tuning will potentially allow the design of catalysts with engineered properties.@en