Activity For CO Oxidation Research Articles

A Tale of Two Sites: Neighboring Atomically Dispersed Pt Sites Cooperatively Remove Trace H2 in CO-Rich Stream.

Single-atom catalysts (SACs) exhibit distinct catalytic behavior compared with nano-catalysts because of their unique atomic coordination environment without the direct bonding between identical metal centers. How these single atom sites interact with each other and influence the catalytic performance remains unveiled as designing densely populated but stable SACs is still an enormous challenge to date. Here, a fabrication strategy for embedding high areal density single-atom Pt sites via a defect engineering approach is demonstrated. Similar to the synergistic mechanism in binuclear homogeneous catalysts, from both experimental and theoretical results, it is proved that electrons would redistribute between the two oxo-bridged paired Pt sites after hydrogen adsorption on one site, which enables the other Pt site to have high CO oxidation activity at mild-temperature. The dynamic electronic interaction between neighboring Pt sites is found to be distance dependent. These new SACs with abundant Pt-O-Pt paired structures can improve the efficiency of CO chemical purification.

PtPd nanoparticles on LaCoO3 with ruthenium in the interfaces for CO oxidation

In this work, trimetallic Pt-Pd-Ru nanoparticles (NPs) loaded on LaCoO3 perovskite were prepared by using LaCo0.9PtxPdyRu0.1-x-yO3 as precursor through citrate complexing sol-gol method and characterized by N2 adsorption/desorption, XRD, H2 Temperature-programmed reduction, XPS, CO-TPD, ICP-OES and TEM techniques. The special structure of the trimetallic catalyst and its catalytic performance for CO oxidation were investigated. The results demonstrated that Pt, Ru and Pd ions were successfully incorporated into the lattice of LaCoO3 to form with perovskite structure. After the reduction treatment, the catalyst Pt-Pd-Ru/LaCoO3 was obtained, which exhibited special structure of Pt surface, Pd sub-surface and Ru interface. The trimetallic Pt-Pd-Ru/LaCoO3 displayed the highest activity and best stability for CO oxidation as compared with corresponding bimetallic and monometallic catalysts. The significant improvement on the catalytic activity was ascribed to the combination of the oxygen vacancies on the surface of LaCoO3 and the highly dispersed NPs. The excellent stability was owing to the special metal-support interaction, that is the Pt-Pd in the NPs are connected and adhered to the support of LaCoO3 by the Ru species in the interface.

Solid Fe Resources Separated from Rolling Oil Sludge for CO Oxidation.

The efficient recycling of valuable resources from rolling oil sludge (ROS) to gain new uses remains a formidable challenge. In this study, we reported the recycling of solid Fe resources from ROS by a catalytic hydrogenation technique and its catalytic performance for CO oxidation. The solid Fe resources, after calcination in air (Fe2O3-H), exhibited comparable activity to those prepared by the calcinations of ferric nitrate (Fe2O3-C), suggesting that the solid resources have excellent recycling value when used as raw materials for CO oxidation catalyst preparation. Further studies to improve the catalytic performance by supporting the materials on high surface area 13X zeolite and by pretreating the materials with CO atmosphere, showed that the CO pretreatment greatly improved the CO oxidation activity and the best activity was achieved on the 20 wt.%Fe2O3-H/13X sample with complete CO conversion at 250 °C. CO pretreatment could produce more oxygen vacancies, facilitating O2 activation, and thus accelerate the CO oxidation reaction rate. The excellent reducibility and sufficient O2 adsorption amount were also favorable for its performance. The recycling of solid Fe resources from ROS is quite promising for CO oxidation applications.

Versatile Layered Hydroxide Precursors for Generic Synthesis of Cu‐Based Materials

The ability to mix multiple elements in a structure is crucial for obtaining Cu‐based nanostructures and microstructures with desirable physicochemical properties. Precursors containing multiple metal cations, such as layered double hydroxides, have been used for the synthesis of multielement materials. However, these precursors experience difficulty containing large cations, which limits the functionalities of the derived materials. Herein, the development of Cu‐based hydroxy double salts (HDSs), versatile precursors that accommodate a broad range of metal cations with homogeneous distributions, is reported. Up to 25 different metal cations are mixed with Cu in an HDS single phase, individually and simultaneously. The HDSs further exhibit useful properties with respect to anion exchange, exfoliation, and phase transformation to metal oxides. During the metal oxide transformation process, the formed crystal structures are mainly dependent on the ionic radius of the secondary metal cations. To prove their utility as precursors, the metal oxides derived from the HDSs are tested and found that they exhibited high catalytic activities for CO oxidation. This study significantly expands the compositional and structural freedom of Cu‐based multi‐elemental materials.

Determination of Intrinsic Active Sites on CuO–CeO2–Al2O3 Catalysts for CO Oxidation and NO Reduction by CO: Differences and Connections

Based on a CeO2–Al2O3 support (CA-T) prepared by two-step incipient wetness impregnation (T-IWI) method, an efficient CuO catalyst supported on CA-T (Cu/CA-T) was successfully developed, which showed better catalytic performance in CO oxidation and NO reduction by CO (NO + CO reaction) together with higher thermal stability than the CuO catalyst loaded on conventional CeO2–Al2O3 support (Cu/CA). Based on the results of HAADF-STEM, Raman spectra, electron paramagnetic resonance, X-ray absorption spectroscopy, ex situ and quasi in situ X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and dynamic oxygen storage capacity (OSC) testing, etc., the microstructure of CuO–CeO2–Al2O3 catalysts, especially the state of Cu species, was systemically investigated. The mechanisms of CO oxidation and NO + CO reactions on Cu/CA and Cu/CA-T catalysts were collaboratively revealed. It was found that the CA-T support with smaller CeO2 particles could facilitate the formation of more highly dispersed CuOx clusters with better redox property. In CO oxidation, more active Cu+ species could be formed on Cu/CA-T under reaction conditions due to the higher reducibility of CuOx clusters on CeO2, which contributed to its superior CO removal efficiency. After aging, a significant decrease in CO oxidation activity was observed on Cu/CA catalyst, which was mainly resulted from the disappearance of highly dispersed CuOx clusters. In clear contrast, for aged Cu/CA-T catalyst, the highly dispersed CuOx clusters could be well preserved, well explaining its much higher catalytic activity and thermal stability than the aged Cu/CA counterpart as probed by the CO oxidation reaction. In NO + CO reaction, besides the formation of more Cu+ sites for CO adsorption and activation, much higher OSC function was also achieved on the Cu/CA-T catalyst. This was due to the higher concentration of surface oxygen vacancies and moderate strength of CuOx–CeO2 interaction on Cu/CA-T, which could effectively promote the NO dissociation into [N] for N2 formation and the transfer of dissociated [O] to CO@Cu+ sites to complete the CO depletion.

Effect of metal-doping (Me = Fe, Ce, Sn) on phase composition, structural peculiarities, and CO oxidation catalytic activity of cryptomelane-type MnO2

Manganese oxides attract considerable attention as redox catalysts for abatement of environmental pollutants due to their relatively high activity and low costs contrary to noble metal catalysts. The present work is focused on the effect of cryptomelane-type MnO 2 catalyst modification with Fe 3+ , Ce 3+ /Ce 4+ , Sn 4+ on their phase composition, structural peculiarities, and catalytic activity in CO oxidation. The samples are investigated by XRD, Raman spectroscopy, XPS, XRF, and comprehensive HRTEM, with their catalytic activity being studied under the model dry conditions and simulated real exhaust conditions comprising CO, O 2 , and water balanced by inert. The Mn 4+ substitution in the cryptomelane structure by Me n+ is revealed to result in its monoclinic distortion, with the Sn- and Fe-doped cryptomelane-type MnO 2 formation being accompanied by the formation of SnO 2 and Fe 1−x Mn x O 3 /Fe 1+x Mn 2−x O 4 , respectively. For Ce-doped samples, the K + presence in the cryptomelane tunnels is essential to stabilize the cryptomelane structure and nanorod morphology. The cryptomelane structure stabilized by only Ce n+ cations is collapsed during the sample calcination to form Mn 2−x Ce x O 3 and Mn 3−x Ce x O 4 , while high Ce content does not favor the formation of the cryptomelane-type MnO 2 . The composites based on the Me-doped cryptomelane-type α-MnO 2 , especially those doped with Ce, are shown to be promising candidates to develop effective oxide-based catalysts for CO oxidation. • Mn 4+ substitution by Me n+ results in monoclinic distortion of cryptomelane structure. • K + ions are essential to stabilize cryptomelane structure and nanorod morphology. • Doped cryptomelane-type MnO 2 is promising for designing of new CO oxidation catalysts.

Biomimetic Tremelliform Ultrathin MnO2/CuO Nanosheets on Kaolinite Driving Superior Catalytic Oxidation: An Example of CO.

Highly efficient three-dimensional (3D) kaolinite/MnO2-CuO (KM@CuO-NO3) catalysts were synthesized by a mild biomimetic strategy. Kaolinite flakes were uniformly wrapped by ultrathin tremelliform MnO2 nanosheets with thicknesses of around 1.0-1.5 nm. Si-O and Al-O groups in kaolinite hosted MnO2 nanosheets to generate a robust composite structure. The ultrathin MnO2 lamellar structure exhibited excellent stability even after calcination above 350 °C. Kaolinite/MnO2 exhibited abundant edges, sharp corners, and interconnected diffusion channels, which are superior to the common stacked structure. Open channels guaranteed fast transportation and migration of CO and O2 during CO oxidation. The synthesized KM@CuO-NO3 achieved a 90% CO conversion efficiency at a relatively low temperature (110 °C). Furthermore, the abundant oxygen vacancies on KM@CuO-NO3 assisted the adsorption and activation of oxygen species and thus enhanced the oxygen mobility and reactivity in the catalytic process. The mechanism results suggest that CuO introduced to the catalyst not only acted as CO active sites but also weakened the Mn-O bond, subsequently improved the mobilities of the oxygen species, which was found to contribute to its high activity for CO oxidation. This study provides new conceptual insights into rationally regulating structural assembly between transition metal oxides and natural minerals for high-performance catalysis reactions.

Enhanced hydrothermal durability of Co3O4@CuO–CeO2 Core-Shell catalyst for carbon monoxide and propylene oxidation

The Co3O4@CuO–CeO2 catalyst with modified core–shell structure was designed to enhance hydrothermal durability and low-temperature for carbon monoxide (CO) and propylene (C3H6) co-oxidation. The Co3O4–CuO–CeO2 (CCC) catalysts are excellent for the simultaneous low-temperature oxidation of CO and hydrocarbons (HC). However, Co3O4 catalysts are susceptible to water poisoning on the surface and sintering during hydrothermal treatment. Therefore, we first attempted to introduce a core–shell structure in the CCC catalysts to enhance hydrothermal durability. Cubic-shaped Co3O4 with excellent stability was synthesized as the core, and a shell composed of CuO and CeO2 was formed through a coating process. The optimal shell thickness was determined considering both gas accessibility and hydrothermal durability. To further enhance the oxidation activity of the Co3O4@CeO2 catalyst, varying amounts of Cu were introduced via incipient wetness impregnation. When an appropriate amount of Cu was impregnated with the Co3O4@CeO2 catalyst, electron transfer was accelerated owing to the redox equilibrium of Cu2+ + Ce3+ ↔ Cu+ + Ce4+; thus, the oxidation activity of the catalyst was improved. The Co3O4@CuO–CeO2 catalyst had excellent CO and C3H6 co-oxidation activities and hydrothermal durability. Thus, the developed catalyst was more advanced than the existing CCC catalysts.

CO Oxidation over Alumina-Supported Copper Catalysts

CO oxidation, one of the most important chemical reactions, has been commonly studied in both academia and the industry. It is one good probe reaction in the fields of surface science and heterogeneous catalysis, by which we can gain a better understanding and knowledge of the reaction mechanism. Herein, we studied the oxidation state of the Cu species to seek insight into the role of the copper species in the reaction activity. The catalysts were characterized by XRD, N2 adsorption-desorption, X-ray absorption spectroscopy, and temperature-programmed reduction. The obtained results suggested that adding of Fe into the Cu/Al2O3 catalyst can greatly shift the light-off curve of the CO conversion to a much lower temperature, which means the activity was significantly improved by the Fe promoter. From the transient and temperature-programmed reduction experiments, we conclude that oxygen vacancy plays an important role in influencing CO oxidation activity. Adding Fe into the Cu/Al2O3 catalyst can remove part of the oxygen from the Cu species and form more oxygen vacancy. These oxygen vacancy sites are the main active sites for CO oxidation reaction and follow a Mars-van Krevelen-type reaction mechanism.

Investigation into support effects for Pt and Pd on LaMnO3

The catalytic properties of Pt and Pd supported on thin-film LaMnO3 were investigated. The LaMnO3 film consisted of an ALD-grown 0.5-nm-thick film supported on a high-surface-area MgAl2O4. Pt and Pd were added to the LaMnO3 films by Atomic Layer Deposition (ALD) and then aged by repeated oxidation and reduction cycles at 1073 K. X-Ray Diffraction (XRD), together with Scanning Transmission Electron Microscopy (STEM)/Energy Dispersive Spectroscopy (EDS) showed that Pt underwent extensive sintering during these redox treatments and formed a Pt-Mn alloy following reduction at 1073 K. Consistent with this, the activity of the supported Pt catalysts for CO oxidation decreased progressively with the number of redox cycles. In contrast to the results for Pt, STEM/EDS results indicated that Pd remained well dispersed on LaMnO3, even after five redox cycles. The Pd catalyst showed high activity for CO oxidation at lower temperatures due to a low activation energy and positive reaction order in CO. XRD results with Rietveld analysis for the Pd catalyst indicated the presence of very large crystallites for PdO on the oxidized catalyst and metallic Pd on the reduced catalyst, inconsistent with the high dispersions measured by STEM and the high CO-oxidation rates. Possible explanations for these observations are discussed.

Designing Highly Efficient Cu2O-CuO Heterojunction CO Oxidation Catalysts: The Roles of the Support Type and Cu2O-CuO Interface Effect.

In this work, a series of Cu2O/S (S = α-MnO2, CeO2, ZSM-5, and Fe2O3) supported catalysts with a Cu2O loading amount of 15% were prepared by the facile liquid-phase reduction deposition–precipitation strategy and investigated as CO oxidation catalysts. It was found that the Cu2O/α-MnO2 catalyst exhibits the best catalytic activity for CO oxidation. Additionally, a series of Cu2O-CuO/α-MnO2 heterojunctions with varied proportion of Cu+/Cu2+ were synthesized by further calcining the pristine Cu2O/α-MnO2 catalyst. The ratio of the Cu+/Cu2+ could be facilely regulated by controlling the calcination temperature. It is worth noting that the Cu2O-CuO/α-MnO2-260 catalyst displays the best catalytic performance. Moreover, the kinetic studies manifest that the apparent activation energy could be greatly reduced owing to the excellent redox property and the Cu2O-CuO interface effect. Therefore, the Cu2O-CuO heterojunction catalysts supported on α-MnO2 nanotubes are believed to be the potential catalyst candidates for CO oxidation with advanced performance.

One-pot phyto-mediated combustion technicality for synthesizing Pd adorned Cu2O@CuO heterojunction with great efficiency in CO oxidation and epoxidation applications

In this work, Pd nanoparticles immobilized Cu2O@CuO heterojunction catalysts were synthesized through a facile one-pot green solution combustion technicality using the pomegranate seed extract as reducing mediator/capping fuel during the combustion process. The findings showed that pomegranate seeds extract within a feasible content of biogenic capping components demonstrate a microspheres Pd/Cu2O@CuO with Hydrangea flower-like fibrous structure, higher porosity, the adaptable ratio of Cu+/Cu2+, and Pd°/Pd2+. Even further, the bio-inspired Pd/Cu2O@CuO heterojunction catalysts were exploited in CO oxidation and olefins epoxidation. The bio-inspired 0.5 wt% Pd/Cu2O@CuO provides 100 % conversion of CO at 99 °C and 99 % for cyclohexene epoxidation compared to 220 °C and 81 % for Cu2O@CuO. CuO and Cu2O NPs offer distinctive active centers for respectively, the dissociation of oxygen and CO oxidation. The nanoscale spacing between CuO and Cu2O zone and Pd NPs dispersion are beneficial to the quick movement of the adatom oxygen over Cu2O to cover the vacancies of oxygen on CuO and thereby enhance the catalytic activity for low-temperature CO oxidation and epoxidation processes through a synergetic mechanism.

Surface modification of MCr2O4 (M = Mg and Zn) by Cu-Doping: Theoretical prediction and experimental observation of enhanced catalysis for CO oxidation

We theoretically investigated surface modification of MCr2O4 (M = Mg and Zn) by Cu-doping and doping effects on catalytic activity for CO oxidation. DFT + U calculations elucidated that Cu-dopants in MCr2O4(111) exist on the surface layer, CO oxidation by Cu-doped MCr2O4(111) occurs through Mars van Krevelen mechanism, rate-determining step (RDS) is the first CO2 desorption with oxygen vacancy (OV) formation, and the catalytic activity is enhanced very much by Cu-doping. Also, we experimentally observed that CO conversion was dramatically improved to 70% by the Cu-doped ZnCr2O4 from 5.2% by non-doped ZnCr2O4 at 300 °C. Bader charge analysis and difference density map show that M atom on the MCr2O4 surface receives electron density from the dissociating O atom in the OV formation step and the Cu-dopant can receive more electron density than Mg and Zn atoms to facilitate the OV formation and accelerate the first CO2 desorption(RDS). This larger capability of Cu-dopant for receiving electron density results from the facts that the Cu atom has large electronegativity and + I oxidation state besides + II in metal oxide but Mg and Zn have small electronegativity and only + II oxidation state.

Dual-template synthesis of defect-rich mesoporous Co3O4 for low temperature CO oxidation

CO oxidation is a benchmark in heterogeneous catalysis for evaluation of redox catalysts due to its practical relevance in many applications and the fundamental problems associated with its very high activity at low temperatures. Among which, Co3O4 is one of the most active non-precious metal catalysts. Exposed crystal planes and cobalt sites are considered to be important for its high catalytic activity. Herein, we demonstrate an enhanced CO oxidation activity by a defect-rich mesoporous Co3O4 that prepared by a designed dual-template method. Two different kinds of silicas are used as hard-templates at the same time, resulting in a defect-rich mesoporous Co3O4 with a surface area as high as 169 m2/g. This catalyst exhibited a very high catalytic activity for low temperature CO oxidation with a light-off temperature at −73 oC under the space velocity of 80,000 mL h-1 gcat-1. Further studies reveal that the high surface area promotes the lattice oxygen mobility, surface rich of Co2+ species and active oxygen species are crucial for the high catalytic activity. Moreover, the dual-template approach paves a way towards the design and construction of high-surface-area mesoporous metal oxides for various applications.

The Interaction of K and O2 on Au(111): Multiple Growth Modes of Potassium Oxide and Their Catalytic Activity for CO Oxidation.

In industrial catalysis, alkali cations are frequently used to promote activity or selectivity. Scanning tunneling microscopy, ambient-pressure X-ray photoelectron spectroscopy, and density-functional calculations were used to study the structure and reactivity of potassium oxides in contact with the Au(111) surface. Three different types of oxides (K2 O2 , K2 O and KOy with y<0.5) were observed on top of the gold substrate at 300-525 K. Initially, small aggregates of K2 O2 /K2 O (1-2 nm in size) were seen at the elbows of the herringbone structure. After increasing the K coverage (>0.15 ML), large islands of the oxide (20-40 nm in size) appeared. These islands contained a mixture of K2 O and KOy (y<0.5). A key correlation was found involving the structure, oxidation state, and chemical activity of the alkali oxide. The small aggregates of potassium oxide had a very high catalytic activity for the oxidation of CO, being much more than plain promoters.

The Interaction of K and O2 on Au(111): Multiple Growth Modes of Potassium Oxide and Their Catalytic Activity for CO Oxidation

AbstractIn industrial catalysis, alkali cations are frequently used to promote activity or selectivity. Scanning tunneling microscopy, ambient‐pressure X‐ray photoelectron spectroscopy, and density‐functional calculations were used to study the structure and reactivity of potassium oxides in contact with the Au(111) surface. Three different types of oxides (K2O2, K2O and KOy with y&lt;0.5) were observed on top of the gold substrate at 300–525 K. Initially, small aggregates of K2O2/K2O (1–2 nm in size) were seen at the elbows of the herringbone structure. After increasing the K coverage (&gt;0.15 ML), large islands of the oxide (20–40 nm in size) appeared. These islands contained a mixture of K2O and KOy (y&lt;0.5). A key correlation was found involving the structure, oxidation state, and chemical activity of the alkali oxide. The small aggregates of potassium oxide had a very high catalytic activity for the oxidation of CO, being much more than plain promoters.

Lattice distortion in Mn3O4/SmOx nanocomposite catalyst for enhanced carbon monoxide oxidation

Activation of lattice oxygen species in oxides is an important research topic for improving catalytic oxidation activity. Herein, we tuned the lattice distortion of Mn3O4 spinel oxide via interfacing with amorphous samarium oxides, which would facilitate the activation of lattice oxygen. The crystalline Mn3O4 dispersed uniformly on the amorphous SmOx with a large surface area, which builds abundant interfaces along with many active sites. The lattice distortion degree can be conveniently regulated by changing Sm amount and calcination temperature. The Sm0.3Mn (Sm/Mn molar ratio is 0.3, the calcination temperature is 400 °C) exhibited the optimal intrinsic activity for CO oxidation. Compared with the pristine Mn3O4, its TOFMn increased by 60%, and the reaction rate in wet conditions (10 vol% H2O) was fourfold faster, superior to most reported MnOx oxide catalysts. Integrating with the various characterizations, the improvement of the intrinsic activity fundamentally originates from the rich reactive oxygen species in the lattice-distorted Mn3O4. What’s more, the Sm0.3Mn exhibited better water resistance and SO2 tolerance. Electron characteristics and characterization results revealed that the full filling of the outer shell orbits of samarium protected the active sites at the interfaces from interacting with water. The weakened capacity for SO2 oxidation decelerated the accumulation of sulfate species. This work provides new insights into the rational modulation of reactive oxygen species and developed a practical catalyst with efficient catalytic CO oxidation activity, and excellent water resistance and SO2 tolerance.

Operando infrared imaging of ozone-assisted catalysis for high-throughput screening of catalytic activity

The interest in applying plasma catalysis for various applications is significantly growing; therefore, a rapid discovery and optimization of catalysts in the plasma system is highly demanded. In this study, a new operando infrared (IR) thermography system was developed for high-throughput screening of the catalytic reactivity in ozone-assisted oxidation under realistic operating conditions. In the developed system, the gas flow was maintained under laminar conditions in a flow-through catalyst bed using a porous disc, and the enthalpy of the system was directly correlated with the catalyst activity. The performance of the developed system was confirmed for ozone decomposition and CO oxidation over different metal loaded-TiO2 catalysts at wide operating parameters. Among four metals tested, Ag exhibited the highest activity for both ozone decomposition and CO oxidation, and its loading amount clearly corresponded with the CO oxidation rate and temperature increase measured by the operando IR thermography. Meanwhile, Mn had poor activity for CO oxidation, despite its high activity for ozone decomposition. Therefore, the operando IR thermography provided a rapid screening and deep understanding of catalysts for ozone-assisted oxidation. Unlike conventional point temperature measurements, IR thermography provides a two-dimensional temperature distribution in the catalyst, which can be sensitive in detecting undesirable “hot-spot” formation. Hence, the developed system can be used as a tool for reaction engineering and catalyst design and development.

Pr-rich cerium-zirconium-praseodymium mixed oxides for automotive exhaust emission control

This study describes the textural, structural, redox properties, oxygen reactivity of two Pr-rich cerium-zirconium-praseodymium (CZP) oxides (Ce0.45Zr0.10Pr0.45O2−x and Ce0.475Zr0.05Pr0.475O2−x) and their catalytic activity for propane and CO oxidation in both stoichiometric and lean conditions, two important reactions for automotive exhaust emission control. The concentration of oxygen vacancies can be tuned by the quantity of Pr3+ cations which depend both on the preparation method and the composition. The Pr4+(4 f1)/Pr3+(4 f2) ratio was accurately determined by magnetic measurement. A highly energetic grinding step was found to double this Pr3+ concentration, resulting in a strong enhancement of the low-temperature reducibility, bulk oxygen mobility and catalytic activity for propane deep oxidation. Pr-rich CZP oxides seem to be less relevant for CO oxidation, which is mainly driven by the specific surface areas. These Pr-rich CZP mixed oxides present better performances for lean conditions, suggesting their possible role in diesel oxidation catalysts applications.

The noble metals M (M = Pd, Ag, Au) decorated CeO2 catalysts derived from solution combustion method for efficient low-temperature CO catalytic oxidation: effects of different M loading on catalytic performances

The noble metal nanoparticles have attracted attention due to their excellent catalytic performance for CO oxidation at low temperatures. M-CeO2 (M = Pd, Ag, Au) catalysts with different atomic ratios of M/Ce were deposited via solution combustion method. Among them, 3 at% Pd-CeO2, 5 at% Ag-CeO2 and 1 at% Au-CeO2 catalysts have better catalytic performances. Especially, 5 at% Ag-CeO2 catalyst shows better low-temperature CO oxidation performance. The catalytic activity for CO oxidation follows the follows the following sequence: 5 at% Ag-CeO2 (T50 = 69 °C) > 3 at% Pd-CeO2 (T50 = 99 °C) >1 at% Au-CeO2 (T50 = 115 °C). Meanwhile, the catalysts are characterized by means of powder x-ray diffraction, scanning electron microscope, transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Brunauer–Emmett–Teller and H2-TPR. The characterization results show that the 5 at% Ag-CeO2 catalyst has excellent catalytic activity due to the good dispersion of Ag nanoparticles, the specific surface area of the material, and the reduction catalyst between different valence ions. Moreover, the surface of the catalyst enhances the mutual synergy, effectively promotes the generation of oxygen vacancies, and increases the active oxygen content of the catalyst surface. Finally, the catalytic mechanism of M-CeO2 catalysts is summarized.