Room-Temperature CO Oxidation Catalyst: Low-Temperature Metal–Support Interaction between Platinum Nanoparticles and Nanosized Ceria

AlN4-Graphene as an efficient catalyst for CO oxidation: a DFT study

DFT investigations suggest that AlN₄-Gr shows high stability and superior catalytic performance towards CO oxidation without CO poisoning.

Unravelling the Different Reaction Pathways for Low Temperature CO Oxidation on Pt/CeO2 and Pt/Al2O3 by Spatially Resolved Structure-Activity Correlations

Spatially resolved operando HERFD-XANES (high energy resolution fluorescence detected X-ray absorption near edge structure) complemented by CO concentration gradient profiles along the catalyst bed (SpaciPro) was used to identify the dominant reaction paths for the low and high temperature CO oxidation on Pt/CeO₂ and Pt/Al₂O₃. At low temperatures, features associated with CO adsorption on Pt were found for both catalysts. During the oxidation reaction light-off, the evolution of the spectral and catalytic profile diverged along the catalyst bed. The CO oxidation rate was high on Pt/CeO₂ from the beginning of the catalyst bed with CO being adsorbed on Pt, whereas low CO conversion due to strong CO poisoning was found on Pt/Al₂O₃. This correlation of the CO concentration gradient with unique insight by HERFD-XANES gave direct proof of the crucial contribution of the Pt-CeO₂ perimeter sites overcoming the CO self-inhibition effect at low temperatures.

Large-Pore Mesoporous CeO2 -ZrO2 Solid Solutions with In-Pore Confined Pt Nanoparticles for Enhanced CO Oxidation

Active and stable catalysts are highly desired for converting harmful substances (e.g., CO, NO_x ) in exhaust gases of vehicles into safe gases at low exhaust temperatures. Here, a solvent evaporation-induced co-assembly process is employed to design ordered mesoporous Ce_x Zr_{1- x} O₂ (0 ≤ x ≤ 1) solid solutions by using high-molecular-weight poly(ethylene oxide)-block-polystyrene as the template. The obtained mesoporous Ce_x Zr_{1- x} O₂ possesses high surface area (60-100 m² g^-1 ) and large pore size (12-15 nm), enabling its great capacity in stably immobilizing Pt nanoparticles (4.0 nm) without blocking pore channels. The obtained mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst exhibits superior CO oxidation activity with a very low T₁₀₀ value of 130 °C (temperature of 100% CO conversion) and excellent stability due to the rich lattice oxygen vacancies in the Ce_0.8 Zr_0.2 O₂ framework. The simulated catalytic evaluations of CO oxidation combined with various characterizations reveal that the intrinsic high surface oxygen mobility and well-interconnected pore structure of the mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst are responsible for the remarkable catalytic efficiency. Additionally, compared with mesoporous Pt/Ce_x Zr_{1- x} O₂ -s with small pore size (3.8 nm), ordered mesoporous Pt/Ce_x Zr_{1- x} O₂ not only facilitates the mass diffusion of reactants and products, but also provides abundant anchoring sites for Pt nanoparticles and numerous exposed catalytically active interfaces for efficient heterogeneous catalysis.

Surpassing the single-atom catalytic activity limit through paired Pt-O-Pt ensemble built from isolated Pt1 atoms

Despite the maximized metal dispersion offered by single-atom catalysts, further improvement of intrinsic activity can be hindered by the lack of neighboring metal atoms in these systems. Here we report the use of isolated Pt₁ atoms on ceria as “seeds” to develop a Pt-O-Pt ensemble, which is well-represented by a Pt₈O₁₄ model cluster that retains 100% metal dispersion. The Pt atom in the ensemble is 100–1000 times more active than their single-atom Pt₁/CeO₂ parent in catalyzing the low-temperature CO oxidation under oxygen-rich conditions. Rather than the Pt-O-Ce interfacial catalysis, the stable catalytic unit is the Pt-O-Pt site itself without participation of oxygen from the 10–30 nm-size ceria support. Similar Pt-O-Pt sites can be built on various ceria and even alumina, distinguishable by facile activation of oxygen through the paired Pt-O-Pt atoms. Extending this design to other reaction systems is a likely outcome of the findings reported here.

Single-atom metal catalysts offer maximized material efficiency, but there is large room to improve the intrinsic activity per metal atom for many reactions. Here, the authors demonstrate that the solution for CO oxidation is to tackle the issue of lacking neighboring Pt atoms in the single-atom Pt1/CeO2 system.

Tuning the structure of bifunctional Pt/SmMn2O5 interfaces for promoted low-temperature CO oxidation activity

The interfacial structure of metal-oxide composite catalysts plays a vital role in heterogeneous catalysis, which is crucial to the adsorption and activation of reactants. Herein, the interfacial effects of bare and Fe/Co/Ni doped SmMn2O5 mullite oxide supported Pt clusters on CO oxidation have been investigated by first-principles based microkinetics analysis. A robust formation of Pt/Mn2 trimer structures is demonstrated at the bifunctional interfaces irrespective of the Ptn cluster's size, which can provide spatially separated sites for CO adsorption and O2 dissociation. The binding strength of CO at the interfacial Pt sites is in the optimal range due to the charge transfer from Pt clusters to oxide, while the strong polarization of Mn2 dimers induced by Pt clusters with stable three-dimensional morphologies can lower the energy barrier of O2 dissociation. Based on the microkinetics analysis, the O2 dissociation is the rate-determining step in the full CO oxidation cycle, and the introduction of Mn-Fe hetero-dimers at the interface is predicted to further enhance the low temperature CO oxidation activity of Pt/SmMn2O5 catalysts.

Tuning Pt-CeO2 interactions by high-temperature vapor-phase synthesis for improved reducibility of lattice oxygen

In this work, we compare the CO oxidation performance of Pt single atom catalysts (SACs) prepared via two methods: (1) conventional wet chemical synthesis (strong electrostatic adsorption–SEA) with calcination at 350 °C in air; and (2) high temperature vapor phase synthesis (atom trapping–AT) with calcination in air at 800 °C leading to ionic Pt being trapped on the CeO₂ in a thermally stable form. As-synthesized, both SACs are inactive for low temperature (<150 °C) CO oxidation. After treatment in CO at 275 °C, both catalysts show enhanced reactivity. Despite similar Pt metal particle size, the AT catalyst is significantly more active, with onset of CO oxidation near room temperature. A combination of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and CO temperature-programmed reduction (CO-TPR) shows that the high reactivity at low temperatures can be related to the improved reducibility of lattice oxygen on the CeO₂ support.

While single-atom catalysts (SACs) have attracted a lot of interest, the nature of the active sites in SACs remains elusive. Here the authors elucidate that depositing single atoms via high temperature synthesis leads to improved reducibility of lattice oxygen on CeO2 yielding low temperature reactivity of Pt catalysts in CO oxidation.

Hybrid Organic-Inorganic Perovskites as Promising Substrates for Pt Single-Atom Catalysts

Single-atom catalysts (SACs) combine the best of two worlds by bridging heterogeneous and homogeneous catalysis. The superior catalytic properties of SACs, however, can hardly be exploited without a suitable substrate. Here, we explore the possibility of using hybrid organic-inorganic perovskites as supporting materials for single transition-metal atoms. By means of first-principles calculations, we predict that single Pt atoms can be incorporated into methylammonium lead iodide surfaces by replacing the methylammonium groups at the outermost layer. The iodide anions at the surface provide potentially uniform anchoring sites for the Pt atoms and donate electrons, generating negatively charged Pt_{1}^{δ-} species that allow for preferential O_{2} adsorption in the presence of CO. Such Pt sites are able to catalyze CO oxidation and may also play a role in CO_{2} reduction. The fundamental understanding generated here will shed light on potential applications of hybrid perovskites in the field of (photo)catalysis.

Tuning the Catalytic Properties of Copper-Promoted Nanoceria via a Hydrothermal Method

Copper-cerium mixed oxide catalysts have gained ground over the years in the field of heterogeneous catalysis and especially in CO oxidation reaction due to their remarkable performance. In this study, a series of highly active, atomically dispersed copper-ceria nanocatalysts were synthesized via appropriate tuning of a novel hydrothermal method. Various physicochemical techniques including electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) were employed in the characterization of the synthesized materials, while all the catalysts were evaluated in the CO oxidation reaction. Moreover, discussion of the employed mechanism during hydrothermal route was provided. The observed catalytic activity in CO oxidation reaction was strongly dependent on the nanostructured morphology, oxygen vacancy concentration, and nature of atomically dispersed Cu2+ clusters.

Promotion of Pt/CeO2 catalyst by hydrogen treatment for low-temperature CO oxidation

Low temperature CO oxidation reaction is known to be facilitated over platinum supported on a reducible cerium oxide. Pt species act as binding sites for reactant CO molecules, and oxygen vacancies on surface of cerium oxide atomically activate the reactant O₂ molecules. However, the impacts of size of Pt species and concentration of oxygen vacancy at the surface of cerium oxide on the CO oxidation reaction have not been clearly distinguished, thereby various diverse approaches have been suggested to date. Here using the co-precipitation method we have prepared pure ceria support and infiltrated it with Pt solution to obtain 0.5 atomic% Pt supported on cerium oxide catalyst, and then systematically varied the size of Pt from single atom to ∼1.7 nm sized nanoparticles and oxygen vacancy concentration at surface of cerium oxide by controlling the heat-treatment conditions, which are temperature and oxygen partial pressure. It is found that Pt nanoparticles in range of 1–1.7 nm achieve 100% of CO oxidation reaction at ∼100 °C lower temperature compared to Pt single atom owing to the facile adsorption of CO but weaker binding strength between Pt and CO molecules, and the oxygen vacancy in the vicinity of Pt accelerates CO oxidation below 150 °C. Based on this understanding, we show that a simple hydrogen reduction at 550 °C for the single atom Pt supported on CeO₂ catalyst induces the formation of highly dispersed Pt nanoparticles with size of 1.7 ± 0.2 nm and the higher concentration of surface oxygen vacancies simultaneously, enabling 100% conversion from CO to CO₂ at 200 °C as well as 16% conversion even at 150 °C owing to the synergistic effects of Pt nanoparticles and oxygen vacancies.

Understanding on effects of Pt size and oxygen vacancy at CeO₂ surface in Pt/CeO₂ catalyst for CO oxidation reaction enables to boost catalytic activity.

Improved NO–CO reactivity of highly dispersed Pt particles on CeO2 nanorod catalysts prepared by atomic layer deposition

Highly dispersed platinum (Pt) nanoparticles are deposited on CeO₂ nanorods via atomic layer deposition (ALD) to improve the catalytic activity towards the NO–CO reaction.

Litchi-peel-like hierarchical hollow copper-ceria microspheres: aerosol-assisted synthesis and high activity and stability for catalytic CO oxidation

Copper-ceria is considered to be a promising system used in exhaust treatment due to its low cost and decent catalytic activity. Herein, we have developed novel litchi-peel-like hollow copper-ceria microspheres with varying Cu contents via an aerosol-assisted route. It is found that the dextrin in the spray solution plays a significant role as a sacrificial template and leads to the formation of this hierarchical hollow structure, in which higher surface area and active CuOx species with higher dispersion result in better catalytic activity compared to the usual hollow samples. The litchi-peel-like sample with 20% Cu exhibits the best reactivity for CO oxidation, namely 50% conversion at 83 °C and 100% conversion at 120 °C. Importantly, this novel copper-ceria sample displays outstanding catalytic stability involving cycle stability, long-term stability and thermal stability, which is attributed to step-stabilized strong interaction between CuOx species and CeO2. The superior catalytic activity and stability beyond commercial 5 wt% Pt/Al2O3 provides it with the potential to be a substitute for Pt-based catalysts in practical applications.

In Situ Formation of Isolated Bimetallic PtCe Sites of Single-Dispersed Pt on CeO2 for Low-Temperature CO Oxidation

Identification of the chemical states of catalytic sites is critical for an atomic-level understanding of catalytic mechanisms. Herein, hydrogen thermal pretreatment of the Pt single atoms on porous nanorods of CeO₂ (Pt₁/ PN-CeO₂) induced the formation of isolated bimetallic PtCe sites as a new type of active center for CO oxidation. The evolutions of Pt₁/ PN-CeO₂ catalysts during the hydrogen pretreatment and CO oxidation were examined by various in situ techniques including infrared, ambient-pressure X-ray photoelectron and X-ray absorption spectroscopy. The experimental results demonstrate that these bimetallic sites can be partially preserved or reoxidized into Pt-O-Ce with a low coordination number with oxygen under realistic conditions, leading to the appropriate CO adsorption and activating the efficient activity of Pt₁/ PN-CeO₂ for CO oxidation at low temperature.

Pt-Embedded CuO x-CeO2 Multicore-Shell Composites: Interfacial Redox Reaction-Directed Synthesis and Composition-Dependent Performance for CO Oxidation

Exploring the state-of-the-art heterogeneous catalysts has been a general concern for sustainable and clean energy. Here, Pt-embedded CuO _x-CeO₂ multicore-shell (Pt/CuO _x-CeO₂ MS) composites are fabricated at room temperature via a one-pot and template-free procedure for catalyzing CO oxidation, a classical probe reaction, showing a volcano-shaped relationship between the composition and catalytic activity. We experimentally unravel that the Pt/CuO _x-CeO₂ MS composites are derived from an interfacial autoredox process, where Pt nanoparticles (NPs) are in situ encapsulated by self-assembled ceria nanospheres with CuO _x clusters adhered through deposition/precipitation-calcination process. Only Cu-O and Pt-Pt coordination structures are determined for CuO _x clusters and Pt NPs in Pt/CuO _x-CeO₂ MS, respectively. Importantly, the close vicinity between Pt and CeO₂ benefits to more oxygen vacancies in CeO₂ counterparts and results in thin oxide layers on Pt NPs. Meanwhile, the introduction of CuO _x clusters is crucial for triggering synergistic catalysis, which leads to high resistance to aggregation of Pt NPs and improvement of catalytic performance. In CO oxidation reaction, both Pt^δ+-CO and Cu⁺-CO can act as active sites during CO adsorption and activation. Nonetheless, redundant content of Pt or Cu will induce a strongly bound Pt-O-Ce or Cu-[O _x]-Ce structures in air-calcinated Pt/CuO _x-CeO₂ MS composites, respectively, which are both deleterious to catalytic reactivity. As a result, the composition-dependent catalytic activity and superior durability of Pt/CuO _x-CeO₂ MS composites toward CO oxidation reaction are achieved. This work should be instructive for fabricating desirable multicomponent catalysts composed of noble metal and bimetallic oxide composites for diverse heterogeneous catalysis.

Room temperature carbon monoxide oxidation based on two-dimensional gold-loaded mesoporous iron oxide nanoflakes

In this work, we fabricate a highly effective catalyst for carbon monoxide oxidation based on gold-loaded mesoporous maghemite nanoflakes which exhibit nearly 100% CO conversion and a very high specific activity of 8.41 molCO gAu-1 h-1 at room temperature. Such excellent catalytic activity is promoted by the synergistic cooperation of their high surface area, large pore volume, and mesoporous structure.

Facets Matching of Platinum and Ferric Oxide in Highly Efficient Catalyst Design for Low-Temperature CO Oxidation

Rational design of supported noble metal is of great importance for highly efficient heterogeneous catalysts. On the basis of the distinct adsorption characteristics of noble metal and transition-metal oxides toward O₂ and CO, the overall catalytic performance of CO oxidation reaction could be further modified by controlling the surface property of the materials to achieve optimal adsorption activity. Here, we studied the influence of facets matching between both platinum and ferric oxide support on CO conversion efficiency. It shows that the activities of four catalysts rank following the order of Pt{100}/α-Fe₂O₃{104} > Pt{100}/α-Fe₂O₃{001} > Pt{111}/α-Fe₂O₃{001} > Pt{111}/α-Fe₂O₃{104}. The strong metal-support interaction and adsorption energy varying with matched enclosed surface are demonstrated by density functional theory based on the projected d-band density of states. Compared with the other three cases, the combination of Pt{100} and α-Fe₂O₃{104} successfully weakens CO poisoning and provides proper active sites for O₂ adsorption. It reveals that the facets matching could be a practicable approach to design catalysts with enhanced catalytic performance.

The production of an efficient visible light photocatalyst for CO oxidation through the surface plasmonic effect of Ag nanoparticles on SiO2@α-Fe2O3 nanocomposites

A process for the photo deposition of noble Ag nanoparticles on a core-shell structure of SiO2@α-Fe2O3 nanocomposite spheres was performed to produce a CO photo oxidation catalyst. The structural analyses were carried out for samples produced using different Ag metal nanoparticle weight percentages on SiO2@α-Fe2O3 nanocomposite spheres by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), UV-vis spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). A computational study was also performed to confirm the existence of the synergic effect of surface plasmon resonance (SPR) for different weight percentages of Ag on the SiO2@α-Fe2O3 nanocomposites. The mechanism for CO oxidation on the catalyst was explored using diffuse reflectance infrared Fourier transform spectroscopy (DRFIT). The CO oxidation results for the Ag (2 wt%)-SiO2@α-Fe2O3 nanocomposite spheres showed 48% higher photocatalytic activity than α-Fe2O3 and SiO2@α-Fe2O3 at stable temperature.

Carbonate-mediated Mars–van Krevelen mechanism for CO oxidation on cobalt-doped ceria catalysts: facet-dependence and coordination-dependence

A facet-dependent carbonate-mediated CO oxidation mechanism is proposed.

Identification of a flattened Pd–Ce oxide cluster as a highly efficient catalyst for low-temperature CO oxidation

An improved deposition method was employed to prepare a Pd/CeO₂ catalyst, which exhibited highly efficient activity in low-temperature CO oxidation (LTO).

Activation of surface lattice oxygen in single-atom Pt/CeO2 for low-temperature CO oxidation

To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of heat wasted in the exhaust. Hence, future generations of catalysts must perform at temperatures that are 100°C lower than current exhaust-treatment catalysts. Achieving low-temperature activity, while surviving the harsh conditions encountered at high engine loads, remains a formidable challenge. In this study, we demonstrate how atomically dispersed ionic platinum (Pt2+) on ceria (CeO2), which is already thermally stable, can be activated via steam treatment (at 750°C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability. A new type of active site is created on CeO2 in the vicinity of Pt2+, which provides the improved reactivity. These active sites are stable up to 800°C in oxidizing environments.

Tuning the Structure of Platinum Particles on Ceria In Situ for Enhancing the Catalytic Performance of Exhaust Gas Catalysts

A dynamic structural behavior of Pt nanoparticles on the ceria surface under reducing/oxidizing conditions was found at moderate temperatures (<500 °C) and exploited to enhance the catalytic activity of Pt/CeO₂ -based exhaust gas catalysts. Redispersion of platinum in an oxidizing atmosphere already occurred at 400 °C. A protocol with reducing pulses at 250-400 °C was applied in a subsequent step for controlled Pt-particle formation. Operando X-ray absorption spectroscopy unraveled the different extent of reduction and sintering of Pt particles: The choice of the reductant allowed the tuning of the reduction degree/particle size and thus the catalytic activity (CO>H₂ >C₃ H₆ ). This dynamic nature of Pt on ceria at such low temperatures (250-500 °C) was additionally confirmed by in situ environmental transmission electron microscopy. A general concept is proposed to adjust the noble metal dispersion (size, structure), for example, during operation of an exhaust gas catalyst.

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet-Selective Atomic Layer Deposition

A facet-selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria-metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.

Transient structural and catalytic behaviour of Pt-particles probed by operando spectroscopy during a realistic driving cycle

Pt catalysts investigated with operando XAS under rapid transient temperature automotive driving cycle conditions.