CO Oxidation Research Articles

Time-resolved surface reaction kinetics in the pressure gap.

We extend the use of our recently developed Near-Ambient Pressure Velocity Map Imaging (NAP-VMI) technique to study the kinetics and dynamics of catalytic reactions in the pressure gap. As an example, we show that NAP-VMI combined with molecular beam surface scattering allows the direct measurement of time- and velocity-resolved kinetics of the scattering and oxidation of CO on the Pd(110) surface with oxygen pressures at the surface up to 1 × 10-5 mbar, where different metastable surface structures form. Our results show that the c(2 × 4) oxide structure formed at low O2 pressure is highly active for CO oxidation. The velocity distribution of the CO2 products shows the presence of two reaction channels, which we attribute to reactions starting from two distinct but rapidly interconverting CO binding sites. The effective CO oxidation reaction activation energy is Er = (1.0 ± 0.13) eV. The CO2 production is suppressed at higher O2 pressure due to the number of antiphase domain boundaries increasing, and the missing row sites are filled by O-atoms at O2 pressures approaching 1 × 10-6 mbar. Filling of these sites by O-atoms reduces the CO surface lifetime, meaning the surface oxide is inactive for CO oxidation. We briefly outline further developments planned for the NAP-VMI and its application to other types of experiments.

Structure and Chemical Reactivity of Y-Stabilized ZrO2 Surfaces: Importance for the Water-Gas Shift Reaction.

The surface structure and chemical properties of Y-stabilized zirconia (YSZ) have been subjects of intense debate over the past three decades. However, a thorough understanding of chemical processes occurring at YSZ powders faces significant challenges due to the absence of reliable reference data acquired for well-controlled model systems. Here, we present results from polarization-resolved infrared reflection absorption spectroscopy (IRRAS) obtained for differently oriented, Y-doped ZrO2 single-crystal surfaces after exposure to CO and D2O. The IRRAS data reveal that the polar YSZ(100) surface undergoes reconstruction, characterized by an unusual, red-shifted CO band at 2132 cm-1. Density functional theory calculations allowed to relate this unexpected observation to under-coordinated Zr4+ cations in the vicinity of doping-induced O vacancies. This reconstruction leads to a strongly increased chemical reactivity and water spontaneously dissociates on YSZ(100). The latter, which is an important requirement for catalysing the water-gas-shift (WGS) reaction, is absent for YSZ(111), where only associative adsorption was observed. Together with a novel analysis scheme these reference data allowed for an operando characterisation of YSZ powders using DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). These findings facilitate rational design and tuning of YSZ-based powder materials for catalytic applications, in particular CO oxidation and the WGS reaction.

Preparation and Evaluation of FeMnTi Monolithic Catalysts for High‐Efficiency CO Oxidation

AbstractA comprehensive study was conducted on the synthesis of FeMnTi monolithic catalysts using plasma electrolytic oxidation (PEO) process combined with hydrothermal method followed by depositing active nanostructures. As synthesized catalysts were characterized using a series of techniques for morphology, structure and surface chemical state investigations. Meanwhile, the CO light‐off curves demonstrate that they possess excellent low‐temperature catalytic performance compared with TiO2 based single transition oxides. Specifically, FeMnTi(0.10, 4) can achieve 100 % conversion at 201 °C, which is due to the homogeneous elements distribution, large surface area and high surface activity. The supersaturation of the deposited solution and deposition time determine the growth of MnOx and the FeMnTi(0.10, 4) has the most suitable Fe/Mn atom ratio of 2.5. Furthermore, the electron transfer between Fe (Fe2+ and Fe3+) and Mn (Mn2+, Mn3+ and Mn4+) ensures the excellent redox properties. The synthetic strategy proposed in this work has general applicability for synthesizing multiple transition oxides monolithic catalysts not only for CO oxidation.

Synergistic growth of nickel and platinum nanoparticles via exsolution and surface reaction

Bimetallic catalysts combining precious and earth-abundant metals in well designed nanoparticle architectures can enable cost efficient and stable heterogeneous catalysis. Here, we present an interaction-driven in-situ approach to engineer finely dispersed Ni decorated Pt nanoparticles (1-6 nm) on perovskite nanofibres via reduction at high temperatures (600-800 oC). Deposition of Pt (0.5 wt%) enhances the reducibility of the perovskite support and promotes the nucleation of Ni cations via metal-support interaction, thereafter the Ni species react with Pt forming alloy nanoparticles, with the combined processes yielding smaller nanoparticles that either of the contributing processes. Tuneable uniform Pt-Ni nanoparticles are produced on the perovskite surface, yielding reactivity and stability surpassing 1 wt.% Pt/γ-Al2O3 catalysts for CO oxidation. This approach heralds the possibility of in-situ fabrication of supported bimetallic nanoparticles with engineered compositional distributions and performance.

Catalytic oxidation of carbon monoxide at low temperature using AuRh/TiO2 bimetallic catalysts: Effect of the synthesis method

AuRh nanoparticles supported on TiO2 P25 were synthesized by two sequential deposition methods: sequential deposition-precipitation with urea (DPU) and impregnation (IMP)-DPU. Segregated nanoparticles (RhcoreAushell ball-cup-type, and Janus-type arrangements) were observed in gold-rhodium bimetallic catalysts, but mainly ball-cup-type and Janus-type nanoparticles were found on catalysts prepared by IMP-DPU. XPS analysis of gold-rhodium bimetallic catalysts, before and after reaction allowed concluding that gold-rhodium interaction on metallic state was an important factor to avoid the oxidation of rhodium during CO oxidation. However, this effect of stabilization of the rhodium metallic phase by gold does not fully explain the promoting effect observed for some bimetallic catalysts on CO oxidation. Some structural aspects such as the atomic arrangement of the bimetallic nanoparticles and the type of active sites, determined by DRIFTS-CO, were also considered. TPR and UV–visible DR spectroscopy characterizations also showed differences in the gold-rhodium interactions.

Understanding the Photoinduced Desorption and Oxidation of CO on Ru(0001) Using a Neural Network Potential Energy Surface

Understanding the Photoinduced Desorption and Oxidation of CO on Ru(0001) Using a Neural Network Potential Energy Surface

Assessing the Intrinsic Activity of Pt‐Group Electrocatalysts for Carbon Monoxide Oxidation: Best Practices and Benchmarking Parameters

AbstractPt‐group elements are the state‐of‐the‐art electrocatalysts for various fuel cells. However, their CO‐poising is a critical hitch for large‐scale applications, so the researchers are exerting huge efforts to solve this issue. The exponentially increasing attention in this field pressures the researchers to publish their findings quickly, leading to unavoidable flawed evaluation parameters for the intrinsic activity of electrocatalysts. The CO oxidation (COOxid) is highly sensitive to various factors. Thus, it is urgent to afford a deeper understanding of the inherent COOxid activity of state‐of‐the‐art electrocatalysts and adopt accurate guidelines for researchers to test, optimize, and compare their electrocatalysts. This review provides exactitude in the evaluation and precise assessment of the key descriptors related to electrocatalysts (i. e., effect of both size, shape, and support) and CO oxidation (i. e., effect of electrolyte, working electrode, and CO surface diffusion). This is besides the fundamental aspects (i. e., COOxid Process, mechanism, measurements, calculations, thermodynamics, and kinetics). Various experimental results from our group and others besides in‐situ analysis were provided to support our deep discussion. Finally, we provide a brief synopsis of the relevant milestones of the up‐to‐date challenges and perspectives.

In situ surface etching strategy for bimetallic MOFs-derived oxides and their catalytic properties

MOFs and their derivatives are excellent carriers with large specific surface area. Here, we propose a new strategy to engineer a supported-Pt core shell MOF-derived metal oxide catalyst. In this work, ZnCo-glycol microspheres were used as sacrificial templates, and the pre-prepared Pt nanoparticles were modified in MOFs during the in situ surface etching strategy. Compared to the ZnCo-2MI-330 and ZnCo–Pt-330, ZnCo–Pt-2MI-330 presents good catalytic activity (T10 = 110 °C,T90 = 123 °C) and excellent stability on CO oxidation reaction. By detailed characterization, ZnCo–Pt-2MI-330 remains the original pore structure of MOFs and provides a larger specific surface area, while the addition of Pt NPs changes the content of active species (the high ratio of Co3+ and active oxygen species) in the metal oxides. More importantly, the strategy effectively improves the noble metal catalysts are apt to lose their activities during the thermal catalytic caused by the serious working environment.

Study on the mechanism of CO oxidation and NO removal by CO-SCR over MFe2O4 (M=Co, Cu, Zn)

Study on the mechanism of CO oxidation and NO removal by CO-SCR over MFe2O4 (M=Co, Cu, Zn)

Effect of cobalt on CeO2 nanorod supported Pt catalyst: Structure, performance, kinetics and reaction mechanism in CO oxidation

Catalytic oxidation represents a highly efficient and extensively employed approach for the elimination of CO in exhaust gas. Rationally designing and preparing catalysts with exceptional activity and stability in the presence of H2O and SO2 at low temperatures represent crucial avenues for future advancements. In this work, a series of Pt catalysts supported on CeO2 nanorods incorporated with varying amounts of Cobalt (Co/CeO2 ratio ranging from 0 to10) were prepared and evaluated for their catalytic activity in CO oxidation under both dry and wet conditions. The ultrahigh dispersion of Pt, outstanding redox properties, and abundant oxygen vacancies on the surface of Co-doped CeO2 nanorod supported Pt catalysts were revealed by XRD, HAADF-STEM, Raman spectroscopy and H2-TPR techniques. The catalytic activity for CO oxidation strongly depends on the Co content and reaction conditions. Among them, Pt/Co-CeO2-5 % exhibits the highest CO oxidation performance with a T90 (the temperature to achieve 90 % conversion of CO) of 170 °C under dry conditions, which is significantly lower by 140 °C compared to T90 of Pt/CeO2. Pt/Co-CeO2-1 % demonstrates superior CO oxidation performance with a T90 of 195 °C under wet conditions, exhibiting a reduction in temperature by 65 °C compared to the T90 of Pt/CeO2. Moreover, Pt/Co-CeO2 exhibits excellent resistance to SO2 compared to Pt/CeO2. Kinetic studies, in situ DRIFT analysis and isotopic experiments demonstrated direct participation of H2O in the reaction. On the catalysts with a low Co/Ce ratio (Co/Ce < 0.03), CO readily reacts with hydroxyl groups dissociated from H2O to form carboxyl intermediates, which subsequently undergo rapid decomposition into CO2, resulting in an enhanced reaction rate of CO oxidation at low temperature.

Remarkable enhancement of CO oxidation over Pt1/CeO2 catalysts by atomically dispersed tungsten

Ceria-supported atomically dispersed Pt is of great interest in CO oxidation due to their unique catalytic performance and high metal utilization. However, the intrinsic activity of the Pt1/CeO2 single atom catalysts may not be desirable due to the overstabilization of Pt2+ species in the CeO2 matrix. Herein, the local environment of Pt2+ species was tailored by introducing a tungsten oxide additive into the Pt1/CeO2 catalyst, achieving a dramatic improvement in catalytic performance for CO oxidation at low temperatures. The optimized catalyst with 2.5 wt% W loading achieved 100 % CO conversion at 150 °C, which was 120 °C lower than that of the unmodified Pt/CeO2 catalyst. Through in situ infrared spectroscopy and temperature-programmed reduction characterizations, as well as theoretical calculations, we concluded that the tungsten additive modulate the interactions between Pt2+ species and CeO2. Thus, the reducibility of Pt was enhanced, which facilitated the formation of catalytically active metallic Pt0 species during the reaction.

Four-channel catalytic micro-reactor based on alumina hollow fiber membrane for efficient catalytic oxidation of CO

The traditional automotive catalytic converter using commercial ceramic honeycomb carriers has many problems such as high back pressure, low engine efficiency, and high usage of precious metals. This study proposes a four-channel catalytic micro-reactor based on alumina hollow fiber membrane, which uses phase inversion method for structural molding and regulation. Due to the advantages of its carrier, it can achieve lower ignition temperature under low noble metal loading. With Pd/CeO2 at a loading rate of 2.3% (mass), the result showed that the reaction ignition temperature is even less than 160 °C, which is more than 90 °C lower than the data of commercial ceramic substrates under similar catalyst loading and airspeed conditions. The technology in turn significantly reduces the energy consumption of the reaction. And stability tests were conducted under constant conditions for 1000 hours, which proved that this catalytic converter has high catalytic efficiency and stability, providing prospects for the design of innovative catalytic converters in the future.

Mechanistic Insights into the Palladium-Catalyzed Perfluoroalkylative Carbonylation of Unactivated Alkenes to β-Perfluoroalkyl Esters: A DFT Study.

Transition metal-catalyzed multicomponent carbonylation is an efficient synthetic strategy to access multifunctional esters in high yields with broad functional group tolerance and good chemoselectivity. Considering the development of highly efficient synthetic methods for esters, it remains significant to grasp the mechanism of constructing multifunctional esters. Herein, density functional theoretical calculations were carried out to acquire mechanistic insight into the synthesis of β-perfluoroalkyl esters from a specific palladium-catalyzed perfluoroalkylative carbonylation of unactivated alkenes using carbon monoxide. A detailed mechanistic understanding of this reaction route includes (1) multistep radical reaction process, (2) C-C coupling and CO insertion, (3) ligand exchange, and (4) Pd-based intermediate oxidation and reductive elimination. The multistep radical process was fundamentally rationalized, including Rf· formation and radicals A and E from unactivated alkene and CO oxidation, respectively. The potential energy calculation indicated that the CO insertion into the perfluorinated alkyl radicals preceded Pd-catalyzed oxidation in the competitively multistep free radical reaction process. In addition, the I-/PhO- exchange step was predicted to be spontaneous to products. The IGMH analysis further attested to the reductive elimination process involved in the rate-determining step. Thus, a simple and valid density functional theory (DFT) approach was developed to reveal the multistep radical mechanism for the Pd-catalyzed perfluoroalkylative carbonylation of unactivated alkenes to access functional β-perfluoroalkyl esters.

Two-dimensional MXene supported Ru-Cr(OH)x clusters as an efficient electrocatalyst for hydrogen oxidation reaction

The development of high-performance non-platinum catalysts remains a key challenge for the practical application of anion-exchange membrane fuel cells due to the sluggish kinetics response of the hydrogen oxidation reaction (HOR) in alkaline electrolytes. Herein, we report an outstanding HOR electrocatalyst using a facile one-step method with the two-dimensional double transition metal MXene (Mo2TiC2Tx) as a carrier mixed with metallic ruthenium and Cr(OH)x clusters (Ru-Cr(OH)x/MXene). Specifically, the as-prepared Ru-Cr(OH)x/MXene electrocatalyst exhibits a high apparent kinetic current (jk) of 18.32 mA cm−2 and exchange current (j0) of 1.64 mA cm−2 at an overpotential of 50 mV, respectively, which are 4.74 and 1.46 times as high as those of Pt/C catalyst. Additionally, mechanism experiments indicated that the Ru-Cr(OH)x/MXene electrocatalyst could attenuate the adsorption of hydrogen intermediate (Had) and enhance the adsorption of hydroxyl species (OHad) to promote CO oxidation, which resulted in a significant increase in the HOR activity and enhanced tolerance to CO. Furthermore, combining theoretical studies via density functional theory calculations, our work confirm that the interaction effect of each components of Ru-Cr(OH)x/MXene can optimize the binding energy of the Had and OHad for the HOR. This work develops a new approach to design of HOR electrocatalyst with MXene-based materials.

Rational one-step synthesis of porous PtAg nanowires for methanol oxidation with a CO-poisoning tolerance: An experimental and theoretical study

Binary Pt-based porous nanowires (PNWs) are highly promising for electrochemical applications owing to their high surface areas, abundant active sites, and immense durability against aggregation, but their simple template-free synthesis for methanol oxidation reaction (MOR) is rarely reported. Herein, we provide a simple and template-free method for the one-step fabrication of PtAgx PNWs via autocatalytic and oriented attachment growth mechanism in an autoclave. This drives the formation of ultra-long PtAg PNWs (∼1.5 µm length and 20 nm width) with agglutinated pores (2–10 nm), high Ag content (22–34 wt%), and upshifted d-band center. These merits endowed the methanol oxidation reaction (MOR) mass activity of PtAg PNWs (2.22 mA/µgPt) by 2.4 and 3.4 times than those of Pt PNWs and commercial Pt/C catalyst, respectively, based on equivalent Pt mass besides a superior stability and CO-poisoning tolerance. The MOR activity of PtAg PNWs outperformed previously reported PtAg nanostructures. Density functional theory (DFT) simulations confirmed the bifunctional MOR mechanism with a lower energy barrier for dissociative adsorption of methanol molecules (0.49 eV) and CO oxidation on PtAg PNWs than Pt PNWs. This study may allow the formation of Pt-based PNWs alloys with various metals for MOR.

In situ exsolution of Pt nanoparticles on low Pt-substituted A-site deficient perovskite for efficient CO oxidation

Platinum nanoparticles often lose their efficacy in challenging working environments. In this study, we developed a novel approach for the preparation of highly dispersed precious metal catalysts. The method involves the utilization of composite materials consisting of PtOx/(LC)0.9MP, achieved through the exsolution of a low Pt substituted A-site deficient perovskite (La0.97Ce0.03)0.9Mn0.99Pt0.01O3 ((LC)0.9MP). This procedure facilitates the in situ exsolution of Pt nanoparticles from (LC)0.9MP through heat treatment under 10 vol% H2/Ar environment. During this process, PtOx undergoes transformation to Pt0, exhibiting a high CO catalytic oxidation activity, with the T100(CO) decreasing from 213 to 141 °C. This capability primarily stems from the substantial number of oxygen vacancies and alterations in Pt species induced by the catalyst during the redox process. The active Pt nanoparticles are strongly integrated on the surface of (LC)0.9MP, demonstrate excellent CO oxidation activity and stability. This performance is attributed to the specific structure of perovskite. Upon reoxidation, these particles do not undergo direct reincorporation into the lattice structure. Instead, NPs result in the formation of stable, anchored oxide nanoparticles. This strategy can be extended to other metals oxides catalysts, thus may help the rational design of highly efficient transition metal oxide-based catalysts and beyond.

Advantages and disadvantages of barium oxide addition to bimetallic Pd-Rh three-way catalysts supported on zirconia-doped alumina

Due to enhanced high-temperature stability, zirconia-stabilized alumina is widely used as a support of three-way catalysts. The addition of barium oxide is known to improve the catalytic performance of the composition. In order to go in-depth about the effects of BaO addition, a series of samples was prepared using nitrates and complex salts as a precursor. The interaction of BaO with alumina was found to change dramatically the metal-support interaction of the latter with metals. Thus, the presence of BaO resulted in the sintering of Pd with the formation of agglomerated Pd0 species, which explains a lower activity in CO oxidation of the BaO-doped samples after thermal treatment. Contrarily, the addition of barium nitrate showed a positive effect, inhibiting the collapse of the porous structure of the support, which was the most crucial and accompanied by the formation of the α-Al2O3 phase when no barium nitrate was added.

Exploring Reversible Redox Behavior in the 6H-BaFeO3-δ (0 < δ < 0.4) System: Impact of Fe3+/Fe4+ Ratio on CO Oxidation.

This work is devoted to evaluating the relationship between the oxygen content and catalytic activity in the CO oxidation process of the 6H-type BaFeO3-δ system. Strong evidence is provided about the improvement of catalytic performance with increasing Fe average oxidation state, thus suggesting the involvement of lattice oxygen in the catalytic process. The compositional and structural changes taking place in both the anionic and cationic sublattices of the catalysts during redox cycles have been determined by temperature-resolved neutron diffraction. The obtained results evidence a structural transition from hexagonal (P63/mmc) to orthorhombic (Cmcm) symmetry. This transition is linked to octahedra distortion when the Fe3+ concentration exceeds 40% (δ values higher than 0.2). The topotactical character of the redox process is maintained in the δ range 0 < δ < 0.4. This suggests that the cationic framework is only subjected to slight structural modifications during the oxygen exchange process occurring during the catalytic cycle.

Unidirectional Electron Transfer on Bismuth-Doped Pt/YMn2O5 for Efficient CO Oxidation as Diesel Oxidation Catalysts

Unidirectional Electron Transfer on Bismuth-Doped Pt/YMn₂O₅ for Efficient CO Oxidation as Diesel Oxidation Catalysts

Dilute RuCo Alloy Synergizing Single Ru and Co Atoms as Efficient and CO‐Resistant Anode Catalyst for Anion Exchange Membrane Fuel Cells

Ruthenium (Ru) is considered a promising candidate catalyst for alkaline hydroxide oxidation reaction (HOR) due to its hydrogen binding energy (HBE) like that of platinum (Pt) and its much higher oxygenophilicity than that of Pt. However, Ru still suffers from insufficient intrinsic activity and CO resistance, which hinders its widespread use in anion exchange membrane fuel cells (AEMFCs). Here, we report a hybrid catalyst (RuCo)NC+SAs/N‐CNT consisting of dilute RuCo alloy nanoparticles and atomically single Ru and Co atoms on N‐doped carbon nanotubes The catalyst exhibits a state‐of‐the‐art activity with a high mass activity of 7.35 A mgRu‐1. More importantly, when (RuCo)NC+SAs/N‐CNT is used as an anode catalyst for AEMFCs, its peak power density reaches 1.98 W cm‐2, which is one of the best AEMFCs properties of noble metal‐based catalysts at present. Moreover, (RuCo)NC+SAs/N‐CNT has superior long‐time stability and CO resistance. The experimental and density functional theory (DFT) results demonstrate that the dilute alloying and monodecentralization of the exotic element Co greatly modulates the electronic structure of the host element Ru, thus optimizing the adsorption of H and OH and promoting the oxidation of CO on the catalyst surface, and then stimulates alkaline HOR activity and CO tolerance of the catalyst.