Catalysts For CO Oxidation Research Articles

Theoretical Study on Pt1/CeO2 Single Atom Catalysts for CO Oxidation

Understanding the influence of structural configurations on catalytic performance is crucial for optimizing atom‐efficient single‐atom catalysts (SACs). In this study, we conducted a density functional theory (DFT) investigation of single Pt atoms positioned at step‐edges and within a solid solution on the CeO2(111) surface. We compared these configurations in terms of thermodynamic stability, electronic properties, and further potential energy surfaces for CO oxidation. Stability studies revealed that the solid solution catalyst exhibits greater stability compared to the step‐edge catalyst. Additionally, the Pt in the solid solution catalyst can effectively activate lattice oxygen atoms, making the catalyst more conducive to the formation of oxygen vacancies. The CO oxidation process was analyzed using the Mars‐van Krevelen mechanism, revealing that the solid solution catalyst possesses a more moderate CO adsorption energy. This, coupled with its lower oxygen vacancy formation energy, leads to reduced energy barriers throughout the CO oxidation cycle. Our findings highlight the strong dependence of catalytic activity on the specific configuration of Pt atoms within the CeO2 matrix, with the solid solution model demonstrating superior catalytic efficiency compared to the step‐edge‐supported Pt catalysts.

Giant Charge Separation-Driving Force Together with Ultrafluent Charge Transfer in TiO2/ZnFe-LDH Photoelectrode via Ferroelectric Interface Engineering.

Hydrogen fuel production using photoelectrochemical (PEC) water-splitting technology is incredibly noteworthy as it provides a sustainable and clean method to alleviate the energy environmental crisis. A highly rapid electron shuttle at the semiconductor/WOC (water oxidation cocatalyst) interface is vital to improve the bulk charge transfer and surface reaction kinetics of the photoelectrode in the PEC water-splitting system. Yet, the inevitably inferior interface transition tends to plague the performance enhancement on account of the collision of hole-electron transport across the semi/cat interface. Herein, we address these critical challenges via inserting ferroelectric layer BTO (BaTiO3) into the semi/cat interface. The embedded polarization electric field induced by ferroelectric BTO remarkably pumped hole transfer at the semiconductor/WOC (TiO2/ZnFe-LDH) interface and selectively tailored the electronic structure of LDH surface-active sites, leading to overwhelmingly improved surface hole transfer kinetics at LDH/electrolyte interface, which minish the electron-hole recombination in bulk and on the surface of TiO2. The TiO2 nanorods encapsulated by ferroelectric-assisted ZnFe-LDH achieve 105% charge separation efficiency improvement and 53.8% charge injection efficiency enhancement compared with pure TiO2. This finding offers a strategic design for electrocatalytic-assisted photoelectrode systems by ferroelectric-pumped charge extraction and transfer at the semiconductor/WOC interface.

Structurally ordered FeCo@FeCoOx@NC dual-shell nanoparticles synthesized under micro-oxygen conditions: An efficient cocatalyst for BiVO4 photoelectrochemical water oxidation

Electrocatalysts are usually integrated onto light-absorbing semiconductors to form efficient photoelectrochemical water-splitting systems. Transition metal oxide nanoparticles serve as excellent electrocatalysts, but exhibit poor performance as cocatalysts for photoelectrodes. To address this issue, a FeCo@FeCoOx@NC dual-shell nanoparticle (consisting of a FeCo alloy core, an intermediate FeCoOx shell, and an outermost graphitic carbon shell) was prepared under micro-oxygen conditions. The FeCo alloy has the dual functions of rapid hole storage and efficient charge transport, while the FeCoOx layer acts as active sites to accelerate the kinetics of the water oxidation reaction and the graphitic carbon protects the internal structure of the nanoparticles. Under the synergistic effect of FeCo@FeCoOx@NC and NiFeOx cocatalysts, the injection efficiency and separation efficiency of BiVO4 photoanode almost reach 100 %, and the photocurrent density reaches 6.85 mA cm−2 (1.23 VRHE, AM 1.5 G), marking the highest reported value to date.

Unveiling the Role of Strong Metal-Support Interactions in Gold-Catalyzed CO Oxidation on MnO2 Polymorphs.

The effectiveness of gold (Au)-based catalysts in CO oxidation is significantly influenced by strong metal-support interactions with surface oxygen structures, the mechanisms of which remain elusive. To investigate this property, we selected γ-MnO2, featuring Mn(-O-)2Mn and Mn-O-Mn structural motifs, and β-MnO2, characterized by Mn-O-Mn linkages, as support materials. The CO oxidation process was investigated by fabricating Au nanoparticles supported on these two MnO2 polymorphs. Our findings reveal that Au supported on β-MnO2 substantially enhanced CO oxidation, in stark contrast to the inhibitory effect observed with Au on γ-MnO2. Using operando diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry, we detected an increase in the production of surface-adsorbed oxygen following Au deposition on β-MnO2. Conversely, Au supported on γ-MnO2 resulted in a diminished capacity for surface oxygen adsorption. The presence of Au+ and Mn2+ ions was identified as pivotal for CO oxidation. Moreover, the engagement of the Mn(-O-)2Mn structure in the reaction was impaired after Au loading on γ-MnO2, and the regeneration of the Mn-O-Mn linkage was similarly hindered. We propose a mechanism for the interactions between Au and the oxygen species associated with Mn(-O-)2Mn and Mn-O-Mn structures on MnO2, offering insights into the divergent catalytic behaviors exhibited by different MnO2 polymorphs.

Effect of flame temperature on structure and CO oxidation properties of Pt/CeO2 catalyst by flame-assisted spray pyrolysis

Flame synthesis offers the potential for the synthesis of structure-controlled catalysts. In this study, Pt/CeO2 nanoparticles were synthesized via flame-assisted spray pyrolysis (FASP) and used as CO oxidation catalysts. The catalysts were synthesized using a burner diffusion flame at three different flame temperatures (maximum flame temperatures, Tf = 1556, 1785, and 2026 K), and their particle structure and CO oxidation activity were evaluated. The synthesized Pt/CeO2 catalysts had a bimodal structure containing 100 nm-scale CeO2 loaded with 10 nm-scale Pt and fine CeO2 less than 10 nm loaded with highly dispersed Pt (less than 1 nm). As the flame temperature increases from 1556 to 2026 K, the formation of fine CeO2 particles dominates, resulting in an increase in BET specific surface area from 7.97 to 112 m2/g and Pt dispersion from 4.67 to 20.6%. Insight into the particle formation routes that determine the catalyst structure is provided by numerical simulation of droplet evaporation in a burner flame. CO oxidation experiments showed that the temperature at which CO conversion reached 100% (T100) decreased from 513 to 378 K with increasing flame temperature in FASP. In addition, the thermal stability test showed that the Pt dispersion after thermal degradation was higher for Pt/CeO2 catalyst made by FASP at Tf = 2026 K than that prepared by the impregnation method, and the T100 for CO oxidation was lower by 20 K.

Catalytic oxidation of CO over CuO@TiO2 catalyst: The relationship between activity and adsorption performance

AbstractThe emission of CO toxic gases seriously endangers environmental safety and human health. At present, the use of catalysts for catalytic oxidation of CO has become the mainstream research direction. In this study, CuO@TiO2 catalysts with different ratios were prepared by solvent hydrothermal method, and the effects of reaction pretreatment temperature and other factors on the catalytic oxidation performance of CO were investigated. The experimental results show that the catalyst can achieve 100% conversion of CO at 115°C under the condition of pretreament at 350°C for 2 h. This excellent performance is due to the uniform distribution of the active component on the surface of the TiO2 support, and the large pore structure constructed by the solvent hydrothermal method enhances the adsorption and activation of CO. This work provides an idea for the preparation of CO oxidation catalysts.

A general flame aerosol route to kinetically stabilized metal-organic frameworks

Metal-organic frameworks (MOFs) are highly attractive porous materials with applications spanning the fields of chemistry, physics, biology, and engineering. Their exceptional porosity and structural flexibility have led to widespread use in catalysis, separation, biomedicine, and electrochemistry. Currently, most MOFs are synthesized under equilibrium liquid-phase reaction conditions. Here we show a general and versatile non-equilibrium flame aerosol synthesis of MOFs, in which rapid kinetics of MOF formation yields two distinct classes of MOFs, nano-crystalline MOFs and amorphous MOFs. A key advantage of this far-from-equilibrium synthesis is integration of different metal cations within a single MOF phase, even when this is thermodynamically unfavorable. This can, for example, produce single-atom catalysts and bimetallic MOFs of arbitrary metal pairs. Moreover, we demonstrate that dopant metals (e.g., Pt, Pd) can be exsolved from the MOF framework by reduction, forming nanoclusters anchored on the MOF. A prototypical example of such a material exhibited outstanding performance as a CO oxidation catalyst. This general synthesis route opens new opportunities in MOF design and applications across diverse fields and is inherently scalable for continuous production at industrial scales.

Dual Cocatalysts on Covalent Organic Framework as Charge Transfer Mediator Facilitating Photocatalytic Water Oxidation

AbstractCovalent organic frameworks (COFs) have been regarded as promising photocatalytic materials. However, the sluggish diffusion of photoinduced charges in a single‐component COF remains the obstacles that have to be overcome. Here, we demonstrate a synthesis of a COF bearing dual cocatalysts Co3O4 and Re complex as photocatalyst for water oxidation. The dual cocatalysts are coordinated on the COF, and enable the spatial separation of photoinduced charges. The generated electrons were attracted to Re moiety, while the holes were localized on Co3O4 cocatalyst for water oxidation to produce O2 product. The synergy of dual cocatalysts of COF promote the charge separation and redox reaction. Moreover, hydroxyl radicals generated from the hydration of COF contribute to O−O bond formation, which is the key step of O2 formation. Accordingly, an excellent O2 production rate of 400 μmol g−1 h−1 under visible light irradiation was obtained. This work may pave the way to the development of highly efficient COF photocatalysts for solar energy conversion.

Highly Water-Resistant Ce-Doped CuMnOx Catalyst for Durable CO Oxidation by Inhibiting Byproducts

Highly Water-Resistant Ce-Doped CuMnO_<i>x</i> Catalyst for Durable CO Oxidation by Inhibiting Byproducts

Supported Binuclear Gold Phosphine Complexes as CO Oxidation Catalysts: Insights into the Formation of Surface‐Stabilized Au Particles

Atomically precise gold phosphine complexes as precursors for supported Au catalysts tested in CO oxidation are presented. Using a variety of analytical techniques, including in situ and operando X‐ray absorption spectroscopy, it is discovered that minor changes in the ligand of the molecular complexes result in significantly different activation behaviors of supported Au catalysts under reaction conditions. When using [Au2(μ2‐POP)2]OTf2 (POP = tetraphenylphosphoxane) as single‐source precursor, an active supported oxidation catalyst in second light‐off is obtained, outperforming a commercial Au/TiO2 and a P‐free Au/Al2O3 reference catalyst. Conversely, using [Au2(μ2‐dppe)2]OTf2 (dppe = diphenylphosphinoethane) on alumina leads to a significant decrease in CO oxidation activity. This difference is attributed to the formation of P‐containing ligand residues on the support in the case of [Au2(μ2‐POP)2]OTf2/Al2O3, which enhances the thermal stability of the Au particles and affects the particle's electronic properties through charge transfer processes. This work provides insights into the dynamic ligand decomposition of molecular gold complexes under reaction conditions and demonstrates the delicate balance between the stabilization of Au particles, clusters, and complexes using ligands and the blocking of active sites. This knowledge will pave the way for the targeted use of molecular transition metal complexes as precursors in synthesizing surface‐stabilized nanoparticles.

Enhancing Activity and Stability of Pd-on-TiO2 Single-Atom Catalyst for Low-Temperature CO Oxidation through in Situ Local Environment Tailoring.

The development of efficient Pd single-atom catalysts for CO oxidation, crucial for environmental protection and fundamental studies, has been hindered by their limited reactivity and thermal stability. Here, we report a thermally stable TiO2-supported Pd single-atom catalyst that exhibits enhanced intrinsic CO oxidation activity by tunning the local coordination of Pd atoms via H2 treatment. Our comprehensive characterization reveals that H2-treated Pd single atoms have reduced nearest Pd-O coordination and form short-distanced Pd-Ti coordination, effectively stabilizing Pd as isolated atoms even at high temperatures. During CO oxidation, partial replacement of the Pd-Ti coordination by O or CO occurs. This unique Pd local environment facilitates CO adsorption and promotes the activity of the surrounding oxygen species, leading to superior catalytic performance. Remarkably, the turnover frequency of the H2-treated Pd single-atom catalyst at 120 °C surpasses that of the O2-treated Pd single-atom catalyst and the most effective Pd/Pt single-atom catalysts by an order of magnitude. These findings open up new possibilities for the design of high-performance single-atom catalysts for crucial industrial and environmental applications.

Recent Advances of Monolithic Metal Mesh‐Based Catalysts for CO Oxidation

AbstractThis review systematically evaluates the research and applications of metal mesh‐based catalysts for CO oxidation. CO is a hazardous gas that affects human health and the environment. Traditional cordierite‐based catalysts have drawbacks such as complex preparation, high costs, poor stability, and limited catalytic activity, necessitating exploration of alternative solutions. Monolithic metal mesh‐based catalysts, using metal substrates like Ti, Cu, Fe, FeCrAl, stainless steel, Al and Ni, could address these problems effectively. Generally, each metal mesh requires specific pretreatments to roughen surface and facilitate the loading of active species. Plasma electrolytic oxidation is particularly effective for Ti and Al mesh. This results in a monolithic metal mesh‐based catalyst with uniform surface distribution and fully exposed active species. The review also summarizes in‐situ preparation strategies for metal mesh‐based catalysts and their progress in CO oxidation. Finally, the development potential of metal mesh‐based catalysts is discussed, emphasizing the significant challenges and future prospects for industrial applications.

Boron nitride nanotube confining selected platinum group metal (PGM=Pd and Pt) single atoms catalysts for efficient CO oxidation: Theoretical insight into confinement effect

Despite platinum group metal have been widely used in catalytic converters, high cost and reaction temperature hindered their application. Inspired by the single-atom catalysts and confinement effect, selected PGM confined on the boron nitride nanotube with vacancy defects for CO oxidation have been systematically investigated. For PGM–BNNT catalysts, CO oxidation would proceed competitively in Eley–Rideal and Langmuir–Hinshelwood pathways. With N vacancy, Pd/Pt-BNNT(6,6) needs 0.33 and 0.28 eV to overcome the reaction barriers through the LH mechanism. The internal of BNNT will provide a more favorable nano-confinement environment than exterior surface, with the more activated adsorbed gases andelectron transfer.

Hydrothermal synthesis of La0.5Sr0.5MnO3 nanostructures for enhanced CO oxidation

This study focuses on the synthesis and characterization of La0.5Sr0.5MnO3 (LSMO) perovskite nanostructures via the hydrothermal method and their catalytic performance evaluation in CO oxidation. Structural analysis using techniques like XRD, FE-SEM, FTIR, and Raman spectroscopy analysis verified the development of LSMO nanostructures exhibiting a rhombohedral phase configuration. The catalytic activity of the annealed LSMO nanostructures was assessed, demonstrating significant CO conversion efficiency attributed to structural modifications enhancing catalytic performance. These findings highlight the potential of LSMO perovskite nanostructures as efficient catalysts for CO oxidation.

Oxidation cocatalyst/S-scheme junction cooperatively assists photocatalytic H2 production in ternary hybrid: The case of PdO@TiO2-Cu2O

Solar-driven photocatalytic hydrogen production from water splitting holds significant potential in addressing the energy crisis and environmental pollution. However, rapid recombination of photogenerated carriers and insufficient surface catalytic reaction kinetics hinder the photocatalytic process. Constructing the catalytic systems with multi-channel charge-separation can effectively alleviate those issues. In this work, ternary PdO@TiO2-Cu2O composites have been synthesized through precursor calcination and low-temperature reduction, where PdO and Cu2O nanoparticles couple with the TiO2 nanorods. Comparing to single TiO2, binary PdO@TiO2 and TiO2-Cu2O, the PdO@TiO2-Cu2O hybrid exhibits enhanced photocatalytic hydrogen production performance (5831μmol g-1h−1), with a hydrogen production rate more than three times that of single TiO2. Based on the band structures of TiO2 and Cu2O, along with the photochemical/electrochemical, in-situ EPR, Photoluminescence (PL) tests, and work function calculations, the formation of an S-scheme heterojunction at the TiO2-Cu2O interface under light illumination facilitates the recombination of electrons in the conduction band (CB) of TiO2 with holes in the valence band (VB) of Cu2O. In this regard, the established built-in electric field significantly accelerates the transfer of photogenerated charges while preserving their respective strong oxidation and reduction capabilities. Meanwhile, the introduction of PdO enriches the holes and further enhances the rate of charge separation. This S-scheme heterojunction with directional charge transfer and oxidation cocatalyst collectively form multi-channels of charge separation, optimizing charge migration and enabling efficient hydrogen production, thus improving the photocatalytic capability of pristine TiO2. This study provides a rational approach to construct efficient S-scheme heterojunction/oxidation cocatalyst multi-component catalytic systems for water splitting into hydrogen.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Dual structure cobalt sites on surface hydroxyl and oxygen vacancy of BiOCl for cooperative CO2 reduction and tetracycline oxidation

Metal ion cocatalysts have huge prospect for photocatalytic CO2 reduction coupled with organic decomposition because of their cost effectiveness and abundant active sites. Herein, we exploit a defect−group oriented tactic to induce dual−structured Co sites on BiOCl with rich surface hydroxyls (OHs) and oxygen vacancies (OVs) (labeled as BiO1−xCl−OH), in which the surface OHs and OVs acted as anchoring points to anchor Co2+ ions. Density functional theory calculations manifested that surface OHs anchored Co2+ ions via hydrogen bonding to produce tight OH−Co sites, meanwhile, surface OVs with unsaturated metal sites and unpaired electrons captured Co2+ ions through chemical bonding to form close−knit OV−Co site. The as−generated OV−Co and OH−Co site served as reductive and oxidative cocatalyst for CO2 reduction and tetracycline oxidation, respectively, thereby achieving high−efficiency redox activity. This work provided a novel strategy to devise progressive dual functional metal ions cocatalysts for high−efficiency CO2 reduction and organic pollutants oxidation.

Enhancing the Performance of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) Perovskites as Catalysts for CO Oxidation by Decreasing the Ba Content.

Mixed oxides featuring perovskite-type structures (ABO3) offer promising catalytic properties for applications focused on the control of atmospheric pollution. In this work, a series of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) samples have been synthesized, characterized and tested as catalysts for CO oxidation reaction in conditions close to that found in the exhausts of last-generation automotive internal combustion engines. All samples were observed to be active as catalysts for CO oxidation during CO-TPRe tests, with Ba0.7MnO3 (B0.7M) being the most active one, as it presents the highest amount of oxygen vacancies (which act as active sites for CO oxidation) and Mn (IV), which features the highest levels of reducibility and the best redox properties. B0.7M has also showcased a high stability during reactions at 300 °C, even though a slightly lower CO conversion is achieved during the second consecutive reaction cycle. This performance appears to be related to the decrease in the Mn (IV)/Mn (III) ratio.

Short-stage synthesis of metal–ceramics composites as precursors for high performance catalytic applications

NiAl, NiCoAl, and CoCuAl intermetallics on ceramic TiC and TiCrC supports were produced by self-propagating high-temperature synthesis (SHS) from granular mixtures and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO2 hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared supported catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO2. It was revealed that 100 % CO conversion is observed in TiC-supported catalysts at 250 °C. Catalysts containing NiCo active phase on both ceramic supports were shown to be the most active in propane oxidation. In CO2 methanation, Ni/TiCrC sample showed the highest CO2 conversion (58.9 % at 350 °C) with 100 % methane selectivity.

Nature of CuxCe1-xO2 solid solution catalysts

Identifying the local environments of active sites of CuxCe1-xO2 solid solution for low-temperature CO oxidation remains significant challenges. In this study, we coupled density functional theory and microkinetic modeling to thoroughly investigate local structures of CuxCe1-xO2 solid solution catalysts, as well as its catalytic performance for low-temperature CO oxidation. Combined with the infrared spectra simulations, we propose that the substitution of Cu3 or Cu4 clusters for one Ce atom accounts for the experimentally observed vibrational peaks of the adsorbed CO, rather than the Cu single atom or dimer. Cu single-atom and Cun clusters (n = 2–4) doped into CeO2 all exhibit an excellent stability against ripening and a promising catalytic activity for low-temperature CO oxidation. This research for the first time elucidates the nature of CuxCe1-xO2 solid solution catalysts and paves the way for the rational design of Cu/CeO2 catalysts for CO oxidation.