Utilizing Quantitative in Situ FTIR Spectroscopy To Identify Well-Coordinated Pt Atoms as the Active Site for CO Oxidation on Al2O3-Supported Pt Catalysts

Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis

Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1-6 nm) by spectroscopically discerning a structure sensitive (CO₂ hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO₂ no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO₂ hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.

Atmosphere-Induced Transient Structural Transformations of Pd-Cu and Pt-Cu Alloy Nanocrystals

We have investigated the transformations of colloidal Pd-Cu and Pt-Cu bimetallic alloy nanocrystals (NCs) supported on γ-Al₂O₃ when exposed to a sequence of oxidizing and then reducing atmospheres, in both cases at high temperature (350 °C). A combination of in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption spectroscopy was employed to probe the NC surface chemistry and structural/compositional variations in response to the different test conditions. Depending on the type of noble metal in the bimetallic NCs (whether Pd or Pt), different outcomes were observed. The oxidizing treatment on Pd-Cu NCs led to the formation of a PdCuO mixed oxide and PdO along with a minor fraction of CuO _x species on the support. The same treatment on Pt-Cu NCs caused a complete dealloying between Pt and Cu, forming separate Pt NCs with a minor fraction of PtO NCs and CuO _x species, the latter finely dispersed on the support. The reducing treatment that followed the oxidizing treatment largely restored the Pd-Cu alloy NCs, although with a residual fraction of CuO _x species remaining. Similarly, Pt-Cu NCs were partially restored but with a large fraction of CuO _x species still located on the support. Our results indicate that the noble metal present in the bimetallic Cu-based alloy NCs has a strong influence on the dealloying/migrations/realloying processes occurring under typical heterogeneous catalytic reactions, elucidating the structural/compositional variations of these NCs depending on the atmospheres to which they are exposed.

Elucidating the surface compositions of Pd@PtnL core-shell nanocrystals through catalytic reactions and spectroscopy probes

The catalytic behaviors or properties of bimetallic catalysts are highly dependent on the surface composition, but it has been a grand challenge to acquire such information. In this work, we employ Pd@Pt_nL core-shell nanocrystals with an octahedral shape and tunable Pt shell thickness as a model system to elucidate their surface compositions using catalytic reactions based upon the selective hydrogenation of butadiene and acetylene. Our results indicate that the surface of the core-shell nanocrystals changed from Pt-rich to Pd-rich when they were subjected to calcination under oxygen, a critical step involved in the preparation of many industrial catalysts. The inside-out migration can be attributed to both atomic interdiffusion and the oxidation of Pd atoms during the calcination process. The changes in surface composition were further confirmed using infrared and X-ray photoelectron spectroscopy. This work offers insightful guidance for the development and optimization of bimetallic catalysts toward various reactions.

Tailoring the Local Environment of Platinum in Single-Atom Pt1 /CeO2 Catalysts for Robust Low-Temperature CO Oxidation

A single-atom Pt₁ /CeO₂ catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over-stabilization of Pt²⁺ in a highly symmetric square-planar Pt₁ O₄ coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt²⁺ by thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt₁ /CeO₂ catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO₂ to generate Pt single atoms in an asymmetric Pt₁ O₄ configuration. Owing to this unique coordination, Pt₁ ^δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance. CO oxidation reactivity on the Pt₁ /CeO₂ _TS catalyst was retained under oxidizing conditions.

Influence of Different Thermal Aging Conditions on Soot Combustion with Catalyst by Thermogravimetric Analysis

Diesel particulates are deposited in the diesel particulate filter and removed by the regeneration process. The Printex-U (PU) particles are simulated as the diesel soot to investigate the influence of thermal aging conditions on soot combustion performance with the addition of catalysts. The comprehensive combustion index S, combustion stability index Rw and peak temperature Tp are obtained to evaluate the combustion performance. Compared with the PU/Pt mixtures of different Pt contents (2 g/ft3, 3.5 g/ft3, and 5 g/ft3), the 10 g/ft3 Pt contents improve soot combustion with the outstanding oxygen absorption ability. When the weight ratio of PU/Pt mixture is 1:1, the promoted effect achieves the maximum degree. The S and Rw increase to 8.90 × 10-8 %2min-2°C-3 and 39.11 × 105, respectively, compared with pure PU. After the thermal aging process, the PU/Pt mixture with a 350 °C aging temperature for 10 h promotes the soot combustion the best when compared to pure PU particles. It is not good as the PU/Pt mixture without aging, because the inner properties of soot and Pt/Al2O3 catalyst may have been changed. The S and Rw are 9.07 × 10-8 %2min-2°C-3 and 38.39 × 105, respectively, which are close to the no aging mixture. This work plays a crucial role in understanding the mechanism of the comprehensive effect of soot and catalyst on soot combustion after the thermal aging process.

The formation and evolution of carbonate species in CO oxidation over mono-dispersed Fe on graphene

Fe is not only the most abundant metal on the planet but is also the key component of many enzymes in organisms that are capable of catalyzing many chemical conversions. Mono-dispersed Fe atoms on carbonaceous materials are single atom catalysts (SACs) that function like enzymes. To take advantage of the outstanding catalytic performance of Fe-based SACs, we extended a CO oxidation reaction network over mono-dispersed Fe atoms on graphene (FeGR) by first-principles based calculations. FeGR-catalyzed CO oxidation is initiated with a revised Langmuir-Hinshelwood pathway through a CO-assisted scission of the O-O bond in peroxide species (OCOO). We showed that carbonate species (CO3), which were previously generally considered as a persistent species blocking reaction sites, may form from CO2 and negatively charged O species. This pathway competes with desorption of CO2 and reduction of the Fe center with gaseous CO, and it is exothermic and inevitable, especially at low temperatures and with high CO2 content. Although direct dissociation of CO3 is demanding on FeGR, further adsorption of CO on Fe in CO3 is plausible and takes place spontaneously. We then showed that adsorbed CO may react with CO3, forming a cyclic-carbonate-like species that dissociates easily to CO2. These findings highlight the reaction condition-dependent formation and evolution of CO3 as well as its contribution to CO conversion, and it may extend the understanding of the performance of SACs in low temperature CO oxidation.

A Comparison of Experimental Procedures for the Application of Infrared Spectroscopy to Probe the Surface Morphology of an Alumina-Supported Palladium Catalyst

Structure/function relationships in heterogeneous catalysis play an important role in catalyst design strategies. The combination of chemisorption of suitable probe molecules alongside application of infrared spectroscopy is an established technique for providing information on the metal crystallite morphology of supported metal catalysts. Following a review of key literature on this topic, a variety of experimental arrangements that may be adopted for this task are examined. Specifically, the adsorption of CO over a 5wt% Pd/Al2O3 catalyst is investigated using transmission and diffuse reflectance sampling options and two research grade spectrometers. Although comparable spectra are obtained on all the platforms examined, differences are noted. In particular, temperature-programmed IR spectroscopy on one platform enables resolution of two features assigned to linear CO bound to the Pd particles. The relevance of this sub-division of terminal sites with respect to selective hydrogenation reactions is briefly considered.

Hydrogenation of benzoic acid derivatives over Pt/TiO2 under mild conditions

Hydrogenation of benzoic acid (BA) to cyclohexanecarboxylic acid (CCA) has important industrial and academic significance, however, the electron deficient aromatic ring and catalyst poisoning by carboxyl groups make BA hydrogenation a challenging transformation. Herein, we report that Pt/TiO₂ is very effective for BA hydrogenation with, to our knowledge, a record TOF of 4490 h^-1 at 80 °C and 50 bar H₂, one order higher than previously reported results. Pt/TiO₂ catalysts with electron-deficient and electron-enriched Pt sites are obtained by modifying the electron transfer direction between Pt and TiO₂. Electron-deficient Pt sites interact with BA more strongly than electron-rich Pt sites, helping the dissociated H of the carboxyl group to participate in BA hydrogenation, thus enhancing its activity. The wide substrate scope, including bi- and tri-benzoic acids, further demonstrates the high efficiency of Pt/TiO₂ for hydrogenation of BA derivatives.

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO₂ support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

Interfacial sites in platinum-hydroxide-cobalt hybrid nanostructures for promoting CO oxidation activity

Metal-oxide/hydroxide hybrid nanostructures provide an excellent platform to study the interfacial effects on tailoring the catalysis of metal catalysts. Herein, a hybrid nanostructure of Pt@Co(OH)2 supported on SiO2 was synthesized by incipient wetness impregnation of Co(OH)2 with the aid of H2O2 and successive urea-assisted deposition-precipitation of platinum nanoparticles. The Fenton-like reaction between Co2+ and H2O2 during the impregnation process facilitates the formation of active interfacial sites. This hybrid nanostructure exhibits much higher catalytic activity towards CO oxidation than Pt/SiO2 nanoparticles with a similar Pt loading and particle size. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to track the CO adsorption processes and to identify the reaction intermediates during CO oxidation. It shows that the OH species at the Pt-OH-Co interfacial sites could readily react with CO adsorbed on neighboring Pt to yield CO2 by forming *COOH intermediates and oxygen vacancies. Under the CO + O2 oxidation conditions, O2 molecules are activated by the oxygen vacancy and react with the CO molecules adsorbed on Pt to generate CO2, via forming the highly active *OOH intermediates as observed by DRIFTS.

DFT calculations for single-atom confinement effects of noble metals on monolayer g-C3N4 for photocatalytic applications

Graphitic carbon nitride, as a very promising two-dimensional structure host for single atom catalysts (SACs), has been studied extensively due to its significant confinement effects of single atoms for photocatalytic applications. In this work, a systematic investigation of g-C3N4 confining noble metal single atoms (NM1@g-C3N4) will be performed by using DFT calculations. The geometric structure calculations indicate that the most favorable anchored sites for the NM1 is located in the six-fold cavity, and the deformed wrinkle space of g-C3N4 helps the NM1 to be stabilized in the six-fold cavity. The electronic structure calculations show that the conduction band of NM1@g-C3N4 moved down and crossed through the Fermi level, resulting in narrowing the band gap of the NM1@g-C3N4. Moreover, the confined NM1 provide a new channel of charge transport between adjacent heptazine units, resulting in a longer lifetime of photo-generated carriers except Ru, Rh, Os and Ir atoms. Furthermore, the d-band centres of NM1 in NM1@g-C3N4 show that Rh1@, Pd1@, Ir1@ and Pt1@g-C3N4 SACs may have better photocatalytic performance than other NM1@g-C3N4 SACs. Finally, Pt1@g-C3N4 SACs are considered to have higher photocatalytic activity than other NM1@g-C3N4 SACs. These results demonstrate that the confinement effects of noble metals on monolayer g-C3N4 not only makes the single atom more stable to be anchored on g-C3N4, but also enhances the photocatalytic activity of the system through the synergistic effect between the confined NM1 and the monolayer g-C3N4. These detailed research may provide theoretical support for engineers to prepare photocatalysts with higher activity.

Metal-incorporated mesoporous oxides: Synthesis and applications

Mesoporous oxides are outstanding metal nanoparticle catalyst supports owing to their well-defined porous structures. Such mesoporous architectures not only prevent the aggregation of metal nanoparticles but also enhance their catalytic performance. Metal/metal oxide heterojunctions exhibit unique chemical and physical properties because of the surface reconstruction around the junction and electron transfer/interaction across the interface. This article reviews the methods used for synthesizing metal-supported hybrid nanostructures and their applications as catalysts for environmental remediation and sensors for detecting hazardous materials.

Potassium-incorporated manganese oxide enhances the activity and durability of platinum catalysts for low-temperature CO oxidation

Potassium-incorporated manganese oxide is demonstrated as an efficient support for fabricating highly active and stable Pt catalysts for low-temperature CO oxidation.

Coordinately unsaturated O2c–Ti5c–O2c sites promote the reactivity of Pt/TiO2 catalysts in the solvent-free oxidation of n-octanol

Coordination unsaturated O_2c–Ti_5c–O_2c of TiO₂ (001) facets promote the formation of low-coordinate Pt metal clusters, which enhances catalytic performance in aerobic 1-octanol oxidation.

Atomically Dispersed Pt-group Catalysts: Reactivity, Uniformity, Structural Evolution, and Paths to Increased Functionality

The development of experimental and computational tools that give accurate and visual active site descriptions has renewed research interest in atomically dispersed metal catalysts. In this perspective, we describe our approach to synthesizing and understanding atomically dispersed Pt-group metals on oxide supports. Using site-specific characterization, we show that these metal species have distinct reactivity from metal clusters. We argue that producing materials where all metal sites have identical local coordination is key to both accurately assessing catalytic properties and achieving single-site behavior. Methods for assessing site uniformity are considered. We show that producing uniform metal species allows us to describe their structure at the atomic scale and understand how this structure evolves under different conditions. Finally, we suggest pathways to increased functionality for atomically dispersed catalysts, through control of their local coordination and steric environment and through cooperativity with different sites.

Catalytic performance promoted on Pt-based diesel oxidation catalyst assisted by polyvinyl alcohol

Eliminating vehicle emission is of importance due to the severe limit value. The work reports a convenient strategy of improving dispersion of platinum-based catalyst with the assistance of polyvinyl alcohol in a varied addition amount. Following the "two-step" annealing techniques, the catalytic performance of the polymer-assisted catalysts in diesel was obviously enhanced because of the improved dispersion of the platinum. Based on experimental results, the long chains of polymer resulting in the steric effect are presumed to isolate platinum ion, inhibiting the aggregation of platinum particles and then improving its dispersion. And the hydroxyl bonding between the polymers could convey electron to platinum species, leading to the lower platinum valence state. Both effects are positive resulting in an excellent NO maximum conversion of around 65% at the optimal introduction of 5 mass% of polymer, as the diesel oxidation catalyst (DOC), which could be inclined to a good purification in the diesel aftertreatment. Hopefully, the convenient research method could initiate the exploration and application of polymer-assisted catalysts for well-dispersed noble metal nanoparticles in eliminating exhaust emission.

Revealing the Correlation between Catalytic Selectivity and the Local Coordination Environment of Pt Single Atom

Single atom catalysts (SACs) have recently attracted great attention in heterogeneous catalysis and have been regarded as ideal models for investigating the strong interaction between metal and support. Despite the huge progress over the past decade, the deep understanding on the structure-performance correlation of SACs at a single atom level still remains to be a great challenge. In this study, we demonstrate that the variation in the coordination number of the Pt single atom can significantly promote the propylene selectivity during propyne semihydrogenation (PSH) for the first time. Specifically, the propylene selectivity greatly increases from 65.4% to 94.1% as the coordination number of Pt-O increases from ∼3.4 to ∼5, whereas the variation in the coordination number of Pt-O slightly influences the turnover frequency values of SACs. We anticipate that the present work may deepen the understanding on the structure-performance of SACs and also promote the fundamental research in single atom catalysis.

Insights into Spectator-Directed Catalysis: CO Adsorption on Amine-Capped Platinum Nanoparticles on Oxide Supports

Introducing spectator molecules to the surface of supported noble metal nanoparticles is an innovative approach to improve the selectivity of heterogeneous catalysts. Colloidal synthesis of the nanoparticles allows researchers to select the spectator and the nanoparticle size, as well as the subsequent particle loading on different supports under well-defined conditions. However, understanding the interplay of the various effects that spectators can have on the catalytic properties of metal surfaces still requires further development. In this work, dodecylamine (DDA) is used to develop insights into the influence of spectator species on the chemical properties of 1.4-3.7 nm colloidal Pt nanoparticles on different supports (powders of Al₂O₃, ZnO, and TiO₂). DDA deposition results in two chemically distinct spectator species on the Pt surface depending on temperature, as evidenced from X-ray photoelectron spectroscopy (XPS). DDA selectively blocks terrace sites on the Pt nanoparticles at room temperature, as apparent from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO as a surface-sensitive probe molecule. The electron donor effect of the amine group in DDA influences the electron densities of the accessible lower coordinated, reactive Pt adsorption sites as indicated from spectral shifts in DRIFTS and XPS. Furthermore, DDA suppresses CO-induced surface reconstruction of the Pt surface and metal-support interactions, although these effects depend on temperature and support composition. Therefore, spectators may be used to adjust the nature of metal nanoparticle-oxidic support interactions. The experimental findings and mechanistic explanations are supported by density functional theory calculations. These results may build a platform in understanding the fundamental properties of amine spectators in Pt-based catalysis, activating specific sites, enhancing site selectivity, acting as sensors, and directing the metal-support interaction.

Selective Hydrogenation of Cinnamaldehyde over the Stepped and Plane Surface of Pd Nanoparticles with Controlled Morphologies by CO Chemisorption

Carbon monoxide (CO) molecules are attracting attention as capping agents that control the structure of metal nanoparticles. In this study, we aimed to control the shape and surface structure of Pd particles by reducing the supported Pd precursor with CO. The reduction of Pd nanoparticles with CO promoted the exposure of step sites and generated spherical and concave-tetrahedral Pd particles on carbon and SiO₂ supports. On the other hand, conventional H₂-reduced Pd particles show a flattened shape. The preferential exposure of the step sites by the adsorbed CO molecules was supported by the density functional theory-calculated surface energy and the Wulff construction. Morphology- and surface-controlled Pd nanoparticles were used to study the surface structure and morphology effects of Pd nanoparticles on cinnamaldehyde (CAL) hydrogenation. With an increase in the fraction of step sites on Pd nanoparticles, the hydrogenation activity and selectivity of hydrocinnamaldehyde (HCAL) increased. On step sites, the adsorption of the C═C bond of CAL proceeded preferentially, and HCAL was efficiently and selectively generated.

Structural changes in noble metal nanoparticles during CO oxidation and their impact on catalyst activity

The dynamical structure of a catalyst determines the availability of active sites on its surface. However, how nanoparticle (NP) catalysts re-structure under reaction conditions and how these changes associate with catalytic activity remains poorly understood. Using operando transmission electron microscopy, we show that Pd NPs exhibit reversible structural and activity changes during heating and cooling in mixed gas environments containing O₂ and CO. Below 400 °C, the NPs form flat low index facets and are inactive towards CO oxidation. Above 400 °C, the NPs become rounder, and conversion of CO to CO₂ increases significantly. This behavior reverses when the temperature is later reduced. Pt and Rh NPs under similar conditions do not exhibit such reversible transformations. We propose that adsorbed CO molecules suppress the activity of Pd NPs at lower temperatures by stabilizing low index facets and reducing the number of active sites. This hypothesis is supported by thermodynamic calculations.

CO oxidation activity of non-reducible oxide-supported mass-selected few-atom Pt single-clusters

Platinum nanocatalysts play critical roles in CO oxidation, an important catalytic conversion process. As the catalyst size decreases, the influence of the support material on catalysis increases which can alter the chemical states of Pt atoms in contact with the support. Herein, we demonstrate that under-coordinated Pt atoms at the edges of the first cluster layer are rendered cationic by direct contact with the Al2O3 support, which affects the overall CO oxidation activity. The ratio of neutral to cationic Pt atoms in the Pt nanocluster is strongly correlated with the CO oxidation activity, but no correlation exists with the total surface area of surface-exposed Pt atoms. The low oxygen affinity of cationic Pt atoms explains this counterintuitive result. Using this relationship and our modified bond-additivity method, which only requires the catalyst-support bond energy as input, we successfully predict the CO oxidation activities of various sized Pt clusters on TiO2.

Infrared spectroscopy data- and physics-driven machine learning for characterizing surface microstructure of complex materials

There is a need to characterize complex materials and their dynamics under reaction conditions to accelerate materials design. Adsorbate vibrational excitations are selective to adsorbate/surface interactions and infrared (IR) spectra associated with activating adsorbate vibrational modes are accurate, capture details of most modes, and can be obtained operando. Current interpretation depends on heuristic peak assignments for simple spectra, precluding the possibility of obtaining detailed structural information. Here, we combine data-based approaches with chemistry-dependent problem formulation to develop physics-driven surrogate models that generate synthetic IR spectra from first-principles calculations. Using synthetic IR spectra of carbon monoxide on platinum, we implement multinomial regression via neural network ensembles to learn probability distributions functions (pdfs) that describe adsorption sites and quantify uncertainty. We use these pdfs to infer detailed surface microstructure from experimental spectra and extend this methodology to other systems as a first step towards characterizing complex interfaces and closing the materials gap.

In situ observations of the structural dynamics of platinum-cobalt-hydroxide nanocatalysts under CO oxidation

The structures, compositions and chemical states of metal catalysts are prone to dynamic changes in response to reaction conditions. In this work, a combination of in situ X-ray absorption fine structure spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy has been used to monitor the temperature-dependent structural dynamics in bimetallic Pt-Co(OH)₂ nanocatalysts during CO oxidation. Alloying with electron-donating Co promotes the catalytic activity of metallic Pt for CO oxidation at low temperature. At elevated temperatures under an oxidation atmosphere, O₂ drives the segregation of the Pt-Co alloy into cobalt oxide and platinum metal, with the extent of alloying sharply decreasing from ∼30% at 300 K to 0 at 473 K. Reduction at high temperature could recover the formation of the Pt-Co alloy with the same alloying extent. The observed structural dynamics could be well correlated with the kinetic behavior of the catalysts. This work highlights the importance of tracking the dynamic structural changes of working catalysts for a correct understanding of their catalytic behavior.

A highly active Rh1/CeO2 single-atom catalyst for low-temperature CO oxidation

Rh₁/CeO₂ SAC is highly active for CO oxidation, which exhibits a high TOF of 0.41 s⁻¹via the Mars–van Krevelen mechanism.