Catalytic CO Oxidation Reaction Research Articles

Highly efficient Rh-doped MnO2 nanocatalysts for complete elimination of CO at room temperature.

Obliteration of carbon monoxide is significant due to its hazardous effect on human health and potential application in different fields. Catalytic CO oxidation at lower temperature is the most convenient method to diminish the toxicity of CO. The low-cost catalysts which are exhibiting higher activity at lower temperature with good stability are in demand. The nanosized Rh-doped MnO2 catalysts have been prepared by dextrose-assisted co-precipitation method. Catalytic CO oxidation reaction was carried out over these prepared nanocatalysts under environmentally suitable conditions. XRD confirms the phase formation of prepared catalysts. These samples exhibit rod-like morphology with thickness of rods of less than 10nm which is substantiated from electron microscopy images. XPS data reveals the oxidation state of Mn (+ 4) and Rh (+ 3). These catalysts are highly active for CO oxidation reaction at lower temperature, and one showed complete CO conversion at room temperature. The time-on-stream studies revealed that these catalysts are highly stable for CO oxidation for several hours. These catalysts are decidedly stable in moist condition and also showed higher activity in the presence of moisture, indicating participation of moisture in the oxidation reaction at above room temperatures.

Identifying the Active Phase of RuO2 in the Catalytic CO Oxidation Reaction, Employing Operando CO Infrared Spectroscopy and Online Mass Spectrometry

Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is combined with online mass spectrometry (MS) to help to resolve a long-standing debate concerning the active phase of RuO2 supported on rutile TiO2 (RuO2@TiO2) during the CO oxidation reaction. DRIFTS has been demonstrated to serve as a versatile probe molecule to elucidate the active phase of RuO2@TiO2 under various reaction conditions. Fully oxidized and fully reduced catalysts serve to provide reference DRIFT spectra, based on which the operando CO spectra acquired during CO oxidation under various reaction conditions are interpreted. Partially reduced RuO2@TiO2 was identified as the most active catalyst in the CO oxidation reaction. This is independent of the reaction conditions being reducing or oxidizing and whether the starting catalyst is the fully oxidized RuO2@TiO2 or the partially reduced RuO2@TiO2.

Operando CO Infrared Spectroscopy and On-Line Mass Spectrometry for Studying the Active Phase of IrO2 in the Catalytic CO Oxidation Reaction

We combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with on-line mass spectrometry (MS) to study the correlation between the oxidation state of titania-supported IrO2 catalysts (IrO2@TiO2) and their catalytic activity in the prototypical CO oxidation reaction. Here, the stretching vibration of adsorbed COad serves as the probe. DRIFTS provides information on both surface and gas phase species. Partially reduced IrO2 is shown to be significantly more active than its fully oxidized counterpart, with onset and full conversion temperatures being about 50 °C lower for reduced IrO2. By operando DRIFTS, this increase in activity is traced to a partially reduced state of the catalysts, as evidenced by a broad IR band of adsorbed CO reaching from 2080 to 1800 cm−1.

Simultaneous removal of NO and CO over Ni-Ce bifunctional catalyst supported by modified activated coke at oxygen-rich condition

The modified activated coke (AC-N) supported Ni-Ce transition metal catalyst prepared by incipient-wetness impregnation method can simultaneously catalyze the ammonia selective catalytic reduction (NH3-SCR) reaction and CO oxidation reaction, realizing the removal of NO and CO under low temperature and oxygen-rich conditions. The Ni-Ce/AC-N catalyst can achieve high-efficiency conversion of NO and CO at 175–250 °C, and the conversion rates of NO and CO are both above 95% in this temperature range. After modified by nitric acid, the active coke support has a stronger interaction with metal components, which is conducive to better dispersion of the active components on the catalyst surface, and improves the specific surface area and redox capacity of the catalyst. The synergistic effect between Ni and Ce results in more Ni2+ and Ce3+ species on the catalyst surface, which is beneficial to the improvement of catalytic activity.

Catalytic CO oxidation reaction over N-substituted graphene nanoribbon with edge defects

Density functional theory calculations, including dispersion effects, are used to demonstrate how substitutional nitrogen atoms can improve the catalytic reactivity of graphene nanoribbons (GNR) with edge defects in the CO oxidation process. It is demonstrated that the addition of nitrogen impurities significantly enhances O2 adsorption on GNR. Carbon atoms near the edges of defects are the most active sites for capturing O2 molecules. The lower adsorption energy of CO relative to O2 implies that the N-modified GNR is resistant to CO poisoning. The Eley-Rideal (E-R) mechanism has activation energies as low as 0.38 eV, making it the most energetically relevant pathway for the CO + O2 reaction. The findings of this study might help in the design of catalysts for metal-free catalysis of CO oxidation.

Three-dimensional strain dynamics govern the hysteresis in heterogeneous catalysis

Understanding catalysts strain dynamic behaviours is crucial for the development of cost-effective, efficient, stable and long-lasting catalysts. Here, we reveal in situ three-dimensional strain evolution of single gold nanocrystals during a catalytic CO oxidation reaction under operando conditions with coherent X-ray diffractive imaging. We report direct observation of anisotropic strain dynamics at the nanoscale, where identically crystallographically-oriented facets are qualitatively differently affected by strain leading to preferential active sites formation. Interestingly, the single nanoparticle elastic energy landscape, which we map with attojoule precision, depends on heating versus cooling cycles. The hysteresis observed at the single particle level is following the normal/inverse hysteresis loops of the catalytic performances. This approach opens a powerful avenue for studying, at the single particle level, catalytic nanomaterials and deactivation processes under operando conditions that will enable profound insights into nanoscale catalytic mechanisms.

High-performance and long-term stability of mesoporous Cu-doped TiO2 microsphere for catalytic CO oxidation

Although the low-temperature reaction mechanism of catalytic CO oxidation reaction remains unclear, the active sites of copper play a crucial role in this mechanism. One-step aerosol-assisted self-assembly (AASA) process has been developed for the synthesis of mesoporous Cu-doped TiO2 microspheres (CuTMS) to incorporate copper into the TiO2 lattice. This strategy highly enhanced the dispersion of copper from 41.10 to 83.65%. Long-term stability of the as-synthesized CuTMS materials for catalytic CO oxidation reaction was monitored using real-time mass spectrum. Isolated CuO and Cu-O-Ti were formed as determined by X-ray photoelectron spectroscopy (XPS). The formation of the Cu-O-Ti bonds in the crystal lattice changes the electron densities of Ti(IV) and O, causing a subsequent change in Ti(III)/Ti(IV) and Onon/OTotal ratio. 20CuTMS contained the highest lattice distortion (0.44) in which the Onon/OTotal ratio is lowest (0.18). This finding may be attributed to the absolute formation of the Cu-O-Ti bonds in the crystal lattice. However, the decrease of Ti(III)/Ti(IV) ratio to about 0.35 of 25CuTMS was caused by the CuO cluster formation on the surface. N2O titration-assisted H2 temperature-programmed reduction and in-situ Fourier transform infrared spectroscopy revealed the properties of copper and effects of active sites.

Au/SBA-15 catalyst prepared by ozone treatment and importance of negatively charged gold in CO oxidation by DRIFTS

There is a lack of consensus on the charge state of active gold species in catalytic CO oxidation reaction. Herein, Au/SBA-15 catalyst was prepared by room temperature ozone treatment. Through diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS), two different gold species, Au0 and Auδ− with CO adsorption at about 2112 cm−1 and 2077 cm−1, were observed on Au/SBA-15. In CO oxidation mixture, the 2077 cm−1 band is completely attenuated while the 2112 cm−1 band retains some intensity. CO–Auδ- bonding is weaker than that of CO–Au0, but CO–Auδ- exhibits higher reactivity towards oxygen. Ozone treatment produces AuOx nanoparticles that is not stable and decomposes to metallic Au gradually. To our best knowledge, this is the first time to identify the presence and importance of Auδ− species for “inert” SiO2 supported gold catalyst.

Dynamic Atom Clusters on AuCu Nanoparticle Surface during CO Oxidation

Supported alloy nanoparticles are prevailing alternative low-cost catalysts for both heterogeneous and electrochemical catalytic processes. Gas molecules selectively interacting with one metal element induces a dynamic structural change of alloy nanoparticles under reaction conditions and largely controls their catalytic properties. However, such a multicomponent dynamic-interaction-controlled evolution, both structural and chemical, remains far from clear. Herein, by using state-of-the-art environmental TEM, we directly visualize, in situ at the atomic scale, the evolution of a AuCu alloy nanoparticle supported on CeO2 during CO oxidation. We find that gas molecules can "free" metal atoms on the (010) surface and form highly mobile atom clusters. Remarkably, we discover that CO exposure induces Au segregation and activation on the nanoparticle surface, while O2 exposure leads to the segregation and oxidation of Cu on the particle surface. The as-formed Cu2O/AuCu interface may facilitate CO-O interaction corroborated by DFT calculations. These findings provide insights into the atomistic mechanisms on alloy nanoparticles during catalytic CO oxidation reaction and to a broad scope of rational design of alloy nanoparticle catalysts.

CO Oxidation on Stepped Rh Surfaces: \u03bcm-Scale Versus Nanoscale

The catalytic CO oxidation reaction on stepped Rh surfaces in the 10−6 mbar pressure range was studied in situ on individual μm-sized high-Miller-index domains of a polycrystalline Rh foil and on nm-sized facets of a Rh tip, employing photoemission electron microscopy (PEEM) and field-ion/field-emission microscopy (FIM/FEM), respectively. Such approach permits a direct comparison of the reaction kinetics for crystallographically different regions under identical reaction conditions. The catalytic activity of the different Rh surfaces, particularly their tolerance towards poisoning by CO, was found to be strongly dependent on the density of steps and defects, as well as on the size (µm vs. nm) of the respective catalytically active surface.Graphic

Versatile Synthesis of Pd and Cu Co-Doped Porous Carbon Nitride Nanowires for Catalytic CO Oxidation Reaction

Developing efficient catalyst for CO oxidation at low-temperature is crucial in various industrial and environmental remediation applications. Herein, we present a versatile approach for controlled synthesis of carbon nitride nanowires (CN NWs) doped with palladium and copper (Pd/Cu/CN NWs) for CO oxidation reactions. This is based on the polymerization of melamine by nitric acid in the presence of metal-precursors followed by annealing under nitrogen. This intriguingly drove the formation of well-defined, one-dimensional nanowires architecture with a high surface area (120 m2 g−1) and doped atomically with Pd and Cu. The newly-designed Pd/Cu/CN NWs fully converted CO to CO2 at 149 °C, that was substantially more active than that of Pd/CN NWs (283 °C) and Cu/CN NWs (329 °C). Moreover, Pd/Cu/CN NWs fully reserved their initial CO oxidation activity after 20 h. This is mainly attributed to the combination between the unique catalytic properties of Pd/Cu and outstanding physicochemical properties of CN NWs, which tune the adsorption energies of CO reactant and reaction product during the CO oxidation reaction. The as-developed method may open new frontiers on using CN NWs supported various noble metals for CO oxidation reaction.

TiC supported single-atom platinum catalyst for CO oxidation: A density functional theory study

The CO oxidation reaction over single-atom Pt catalyst dispersed on the defective TiC (1 0 0) surface with a Ti vacancy is studied using the dispersion-corrected density functional theory (DFT-D) computations. The stable configuration of the TiC supported single Pt atoms and the preferable CO oxidation reaction mechanisms are explored. The results demonstrate that the Pt atom may be tightly embedded in the surface Ti defect sites with a formation energy of −4.86 eV, forming a TiC supported single-atom platinum catalyst, marked as Pt@d-TiC. The adsorption characteristics of various adsorbates on Pt@d-TiC are investigated, and the Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanisms for CO oxidation on Pt@d-TiC are simulated. Specifically, it is found that all the reaction species prefer to be adsorbed on the TiC support, indicating that the support vigorously participates in the catalytic reactions. In addition, the catalytic CO oxidation reaction over Pt@d-TiC favors to start with the L–H reaction. The rate-limiting step is the formation of the peroxide-like (OCOO) intermediate complex by the coadsorbed CO and O2 with an activation barrier of 0.91 eV. The subsequent E–R reaction has a lower energy barrier of 0.45 eV. This work clearly shows the catalytic activity of the single-atom Pt supported on TiC for CO oxidation and perhaps for other reactions.

Preparation of PdCu Alloy Nanocatalysts for Nitrate Hydrogenation and Carbon Monoxide Oxidation

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al2O3 with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO2 and CeO2 supports with high oxygen storage capacity. Implications of the results to the refinement of the preparation of the alloy nanocatalysts are also discussed.

Ordered intermetallic Pt–Cu nanoparticles for the catalytic CO oxidation reaction

Intermetallic platinum (Pt) nanoparticles using the abundantly available element copper (Pt3Cu, PtCu, PtCu3) with an average particle size of 4–5 nm on a γ-Al2O3 support were prepared to reduce the consumption of Pt for the removal of CO from gases.

Synthesis, characterization and catalytic properties of La(Ni,Fe)O3–NiO nanocomposites

Nanocomposite structures involving LaNiO3 perovskite partially substituted with iron and segregated NiO are synthesized by sol–gel method using citric acid as chelating agent. Thermogravimetric and differential thermal analysis and X-ray diffraction (XRD) techniques are used to explore precursor decomposition and to establish adequate calcination temperature for the preparation of the nanocomposites. The samples obtained after calcination at 750 °C were characterized by XRD, X-ray photoelectronic spectroscopy, Brunauer–Emmett–Teller surface area analysis, Fourier transform infrared spectroscopy and powder size distribution, and tested for the catalytic oxidation reaction of CO. Optimum catalytic properties are shown to be achieved for nanocomposites with relatively weak Fe/Ni substitution degree in the perovskite interacting with well-dispersed small NiO entities.

Synthesis of TiO2 with diverse morphologies as supports of manganese catalysts for CO oxidation

The catalytic CO oxidation reaction has been investigated over a series of Mn/TiO2 catalysts. The titanium dioxides, including several mesoporous structures were prepared by different synthesis procedures. The mesoporous TiO2 synthesized using evaporation-induced self-assembly (EISA) method exhibited the highest surface area (217.14 m2/g). The successful loading of the active manganese component (2 %) to TiO2 supports showed high dispersion of MnO x species in amorphous state. Characterizations of XRD, N2 adsorption–desorption, pore size distributions, TEM, H2-TPR and XPS were applied to contrast their structure properties and correlated with the corresponding catalytic performance. The Mn/EISA exhibited the highest catalytic activity among the series of Mn/TiO2 catalysts, which could completely oxidize CO into CO2 at temperature as low as 270 oC, due to its highly ordered mesoporous channels, which effectively enlarge the surface area leading to promoting a strong interaction between MnO x species (68 % Mn3+) and TiO2 support.

Iridium ultrasmall nanoparticles, worm-like chain nanowires, and porous nanodendrites: One-pot solvothermal synthesis and catalytic CO oxidation activity

We report a facile one-pot solvothermal synthesis of monodisperse iridium (Ir) ultrasmall (1.5–2.5 nm in diameter) nanoparticles (NPs), worm-like chain nanowires (NWs), and porous nanodendrites (NDs), for which CO oxidation reaction has been employed as a probe reaction to investigate the effects of nanoparticle size and surface-capping organics on the catalytic activities. Time-dependent experiments revealed that an oriented attachment mechanism induced by the strong adsorption of halide anions (Br− and I−) on specific facet of Ir nanoclusters or by decreasing the reduction rate of Ir precursors with changing their concentrations during the synthesis was responsible for the formation of Ir NWs and NDs. Annealing tests indicated that an O2-H2 atmosphere treatment turned out to be an effective measure to clean up the surface-capping organics of Ir NPs supported on commercial SiO2. Catalytic CO oxidation reaction illustrated that a significant improvement in the catalytic activity of CO oxidation reaction was achieved together with the changing of activation energies after such atmosphere treatment for the supported catalysts of the ultrasmall Ir NPs. It is noteworthy that this enhancement in catalytic activity could be ascribed to the changes in the surface status (including populations of Ir species in metallic and oxidized states, removal of surface capping organics, the variety of active sites, and total effective active site number) for the supported nanocatalysts during the atmosphere treatment.

Facile synthesis of Co₃O₄@CNT with high catalytic activity for CO oxidation under moisture-rich conditions.

The catalytic oxidation reaction of CO has recently attracted much attention because of its potential applications in the treatment of air pollutants. The development of inexpensive transition metal oxide catalysts that exhibit high catalytic activities for CO oxidation is in high demand. However, these metal oxide catalysts are susceptible to moisture, as they can be quickly deactivated in the presence of trace amounts of moisture. This article reports a facile synthesis of highly active Co3O4@CNT catalysts for CO oxidation under moisture-rich conditions. Our synthetic routes are based on the in situ growth of ultrafine Co3O4 nanoparticles (NPs) (∼2.5 nm) on pristine multiwalled CNTs in the presence of polymer surfactant. Using a 1% CO and 2% O2 balanced in N2 (normal) feed gas (3-10 ppm moisture), a 100% CO conversion with Co3O4@CNT catalysts was achieved at various temperatures ranging from 25 to 200 °C at a low O2 concentration. The modulation of surface hydrophobicity of CNT substrates, other than direct surface modification on the Co3O4 catalytic centers, is an efficient method to enhance the moisture resistance of metal oxide catalysts for CO oxidation. After introducing fluorinated alkyl chains on CNT surfaces, the superhydrophobic Co3O4@CNT exhibited outstanding activity and durability at 150 °C in the presence of moisture-saturated feed gas. These materials may ultimately present new opportunities to improve the moisture resistance of metal oxide catalysts for CO oxidation.

A near-ambient-pressure XPS study on catalytic CO oxidation reaction over a Ru([formula omitted]) surface

We investigated the interactions of CO and O2 with Ru(101¯0) single crystal surfaces, and studied the in-situ catalytic oxidation reaction of CO on the surface under near realistic pressure conditions by using a combination of near-ambient-pressure x-ray photoelectron spectroscopy and differential pumping mass spectroscopy. At lower temperatures (T<190°C), most of the surface keeps metallic and is covered by both chemisorbed atomic oxygen and CO, and the CO2 formation rate is relatively slow. At higher temperatures, the reaction rate significantly increases and reaches the saturation, where the Ru surface is dominated by a bulk oxide (i.e. RuO2).

In Situ Photoemission Observation of Catalytic CO Oxidation Reaction on Pd(110) under Near-Ambient Pressure Conditions: Evidence for the Langmuir–Hinshelwood Mechanism

CO oxidation reaction on a Pd(110) single crystal surface at various temperatures under near-ambient-pressure conditions has been investigated using in situ X-ray photoemission spectroscopy and mass spectroscopy. At lower temperature conditions, the CO2 formation rate is low, where the surface is covered by CO molecules (i.e., CO poisoning). Above a critical temperature 165 °C the Pd(110) surface converts to a catalytically active surface and is dominated by chemisorbed oxygen species. Further at the higher temperatures up to 320 °C, the CO2 formation rate is gradually decreased to about 80% of the maximum rate. At this moment, the amount of chemisorbed O was also decreased, which suggests that the CO oxidation reaction proceeds via the conventional Langmuir–Hinshelwood mechanism even under near-ambient pressure conditions.