Activity In CO Oxidation Reaction Research Articles

New and Facile Preparation Method for Highly Active Iron Oxide Catalysts for CO Oxidation

This work presents a new and facile route for the preparation of iron oxide-based catalysts supported on alumina, which enables the targeted synthesis of catalysts with an increased amount of isolated tetrahedrally coordinated iron centers compared to a conventional impregnation procedure, and therefore leads to an increase in activity for CO oxidation reaction. By a multi-step impregnation–calcination protocol, the catalysts were synthesized with iron loadings of between 1 and 10 wt%, and their catalytic activity was then compared with a 10 wt% loaded catalyst prepared by conventional single impregnation. With a loading of 8 wt%, the presented catalysts showed an improved catalytic activity regarding light-off and full conversion temperatures compared to this reference. Through the application of several analytical methods (PXRD, PDF, DRUVS, SEM, XAFS), the improved catalytic activity can be correlated with an increased amount of isolated iron centers and a significantly reduced fraction of agglomerates or particles.

SAXS Application for the Determination of the Gold Nanoparticle Sizes in Au/C Catalysts: Advantages over Other Methods

In the case of Au/C catalysts have been shown advantages of application SAXS with masking liquid technique for determining supported metal particle sizes compared with TEM and XRD as standard methods. According to SAXS data particle size distributions of gold in a wide range (1–50 nm) were obtained with full consideration of all size fractions of particles present in the samples under study. Also values of the mass fraction of “X-ray amorphous” gold particles with size less than 4 nm (WSAXS) were determined. It has been found that the oxidative treatment of the carbon support before deposition of metallic gold precursor complexes has a significant effect on the size distribution of gold particles in the final catalyst. Comparison of the results of measuring the rate of CO oxidation by an excess of moist air at 40°C on Au/C catalysts with the (WSAXS) values found for these catalysts showed that the catalytic activity increases exponentially as (WSAXS) increases. High activity in CO oxidation reaction was demonstrated by Au/C catalysts with (WSAXS) ≥ 80%.

Interior surface (confinement effect) and exterior (odd-even effect) of Fe-BNNTs (n, 0) for CO oxidation: A computational view

In this work, a series of Fe embedded boron and nitrogen nanotubes, (Fe-BNNTs (n, 0)B-vacancy, n = 8–13) are chosen to explore the catalytic activity for CO oxidation reaction. For the interior surface, CO oxidation reaction can only proceed on the Fe-BNNTs (n, 0) (n = 9–12) via Langmuir-Hinshelwood (LH) mechanism. Among four Fe-BNNTs with different tube diameters, the Fe-BNNT (12, 0)in exhibits superior catalytic activity, owe to its excellent confinement effect and being an ideal reaction vessel. For the exterior surface, the interesting odd-even effect of n is found: because of moderate O2 adsorption energies Ead (O2) and negative Gibbs free energies (G), only Fe-BNNTs (n, 0) (n = 9, 11 and 13 (odd)) can catalyze CO oxidation reaction via LH and Eley-Rideal (ER) mechanisms, in which (11, 0)out exhibits excellent catalytic activity. Besides, the catalytic activity of interior surface is superior to that of exterior surface. We hope this work can provide a new option to enhance the catalytic activity of non-noble catalysts based on nanotubes.

Temperature-Limited Synthesis of Copper Manganites along the Borderline of the Amorphous/Crystalline State and Their Catalytic Activity in CO Oxidation.

Copper manganese oxides (CMO) with CuMn2O4 composition are well-known catalysts, which are widely used for the oxidative removal of dangerous chemicals, e.g., enhancing the CO to CO2 conversion. Their catalytic activity is the highest, close to those of the pre-crystalline and amorphous states. Here we show an easy way to prepare a stable CMO material at the borderline of the amorphous and crystalline state (BAC-CMO) at low temperatures (<100 °C) followed annealing at 300 °C and point out its excellent catalytic activity in CO oxidation reactions. We demonstrate that the temperature-controlled decomposition of [Cu(NH3)4](MnO4)2 in CHCl3 and CCl4 at 61 and 77 °C, respectively, gives rise to the formation of amorphous CMO and NH4NO3, which greatly influences the composition as well as the Cu valence state of the annealed CMOs. Washing with water and annealing at 300 °C result in a BAC-CMO material, whereas the direct annealing of the as-prepared product at 300 °C gives rise to crystalline CuMn2O4 (sCMO, 15–40 nm) and ((Cu,Mn)2O3, bCMO, 35–40 nm) mixture. The annealing temperature influences both the quantity and crystallite size of sCMO and bCMO products. In 0.5% CO/0.5% O2/He mixture the best CO to CO2 conversion rates were achieved at 200 °C with the BAC-CMO sample (0.011 mol CO2/(m2 h)) prepared in CCl4. The activity of this BAC-CMO at 125 °C decreases to half of its original value within 3 h and this activity is almost unchanged during another 20 h. The BAC-CMO catalyst can be regenerated without any loss in its catalytic activity, which provides the possibility for its long-term industrial application.

Photochemical formation of bimetallic composite meso-TiO2/Ag/Cu with superb photocatalytic activity in CO oxidation reaction

Photochemical formation of bimetallic composite meso-TiO2/Ag/Cu with superb photocatalytic activity in CO oxidation reaction

(Ln1.8Fe0.2)FeSbO7 (Ln = Pr–Tb) Mixed Oxides with the Pyrochlore Structure in CO Oxidation Reaction

(Ln1.8Fe0.2)FeSbO7 (Ln = Pr–Tb) mixed oxides have been synthesized via coprecipitation followed by annealing. According to Rietveld refinement results, all of the oxides have the pyrochlore structure (sp. gr. Fd$$\bar {3}$$mz). The (Ln1.8Fe0.2)FeSbO7 compounds have been shown to exhibit high activity for CO oxidation reaction. The best results have been obtained for (Pr1.8Fe0.2)FeSbO7, which has a 90% CO conversion temperature T90 = 385°C. With increasing lanthanide atomic number, T90 rises monotonically from 385 to 550°C in going from Pr to Tb. This behavior is most likely due to the decrease of structural imperfection in the compounds with smaller lanthanide ionic radii.

Probing the origin of the enhanced catalytic performance of sp3@sp2 nanocarbon supported Pd catalyst for CO oxidation

Tuning the fine structure of carbon support is crucial for modifying the metal-support interface (MSI) in order to harvest a high-performance catalysis. Herein, a core–shell sp3@sp2 nanocarbon (nanodiamond@graphene, ND@G) and a pure sp2 carbon derivative (onion-like carbon, OLC) were applied to support Pd nanoparticles. We found that Pd/ND@G displayed a superior catalytic activity for CO oxidation reaction with a TOF of 2.9 times higher than that of Pd/OLC at 46 °C. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) revealed that, different with the Pd/OLC system, a unique interface microstructure was formed in Pd/ND@G, which not only provides a high exposure of active sites, but also enhances the Pd surface reactivity toward oxygen species, thus leading to a superior catalytic activity of Pd/ND@G. Moreover, the temperature-programmed surface reaction (TPSR) results showed that CO oxidation on Pd/ND@G undergoes an unusual termolecular Eley–Rideal (TER) mechanism, which has a lower energy barrier as compared to the traditional Langmuir-Hinshelwood (LH) and ER mechanism.

Oxalato complexes of Pd(II) with Co(II) and Ni(II) as single-source precursors for bimetallic nanoalloys

The single-source precursors of noble–ignoble nanoalloys are of a great interest since they can be used in many areas such as optical, biomedical, catalysis, magnetic and chemosensors. The new water-soluble double complex salts (DCSs) with aqua and oxalato ligands, [M(H2O)6][Pd(Ox)2]·nH2O (M = Co2+, Ni2+; n = 2, 4; Ox = C2O 4 2− ), were obtained, structurally characterized (single-crystal XRD) and used as precursors for M–Pd nanoalloys. Complexes, intermediate and final thermolysis products were studied by simultaneous thermogravimetric analysis combined with mass spectrometry, powder XRD, in situ synchrotron powder XRD, IR and X-ray photoelectron spectroscopy. Decomposition in different atmospheres leads to formation of bimetallic solid solution M0.5Pd0.5 (He, H2) or a mixture of metal oxides (O2). The catalysts M–Pd/TiO2 (1% Pd) were prepared by the decomposition of DCSs deposited onto titania via wetness impregnation. The H2-made Ni-containing samples showed a high photocatalytic activity in CO oxidation reaction.

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

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

Highly Active CeO2 Nanocatalysts for Low-Temperature CO Oxidation

Ceria (CeO2) nanocatalysts were synthesized by three different methods via a simple sol–gel method (SGM), precipitation method (PPM), and solution combustion method (SCM) for CO oxidation reaction. The results show that the CeO2 catalysts prepared by SGM possess small crystallite size (9 nm), more lattice defects (active sites), high specific surface area (188 m2 g–1), and better thermal stability. Raman spectra showed that large number oxygen vacancies were possessed by CeO2-SGM catalysts as compared to CeO2-PPM and CeO2-SCM. It was observed that the catalytic activity for CO oxidation reaction is greatly influenced by the preparation method. The order of activity and stability of CeO2 material prepared by different methods for CO oxidation process is as follows: CeO2-SGM > CeO2-PPM > CeO2-SCM, respectively.

Exploring different reaction mechanisms for oxidation of CO over a single Pd atom incorporated nitrogen-doped graphene: A DFT study

Single-metal catalysts have attracted particular interests in recent years due to their outstanding catalytic activity in CO oxidation reaction. In the present study, periodic DFT calculations are performed to investigate possible reaction mechanisms for oxidation of CO over a single Pd atom incorporated nitrogen-doped graphene. According to our results, the formation energy of a single-vacancy decreases by incorporation of pyridinic nitrogen atoms in graphene. The Pd atom can be stably anchored over the vacancy site, as evidenced by the large energy barriers for diffusion of the Pd atom to its neighboring sites. It is found that the incorporation of nitrogen atoms makes a significant increase in the adsorption energy of O2 and CO molecules over the supported Pd atom. The latter can be attributed to the shift in the bonding states of the Pd towards the Fermi level, which facilitates the charge-transfer from the 4d orbitals of this atom to the 2π∗ orbitals of O2 and CO molecules. The CO oxidation over the Pd atom supported nitrogen-doped graphene can proceed via three different mechanisms; namely, Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and termolecular Eley-Rideal (TER) mechanisms. Our calculations reveal that the TER mechanism is preferred over the LH and ER, due to its smaller activation energy. The CO oxidation via the TER mechanism is a thermodynamically favorable process over the supported Pd atom, due to a large negative change in the Gibbs free energy of this reaction. The findings of this study can be useful to design more efficient single-atom catalysts to remove toxic CO molecules.

Pt-CeO₂ Catalysts Synthesized by Glucose Assisted Hydrothermal Method: Impact of Calcination Parameters on the Structural Properties and Catalytic Performance in PROX-CO.

We synthesized Pt supported catalysts by the glucose assisted hydrothermal method, in which a carbon template was used to form a porous CeO2 structure upon calcination. Special emphasis was given to evaluate the influence of calcination parameters in the structural and textural properties of the catalysts and the final impact in the catalytic activity of CO oxidation reaction under hydrogen rich atmosphere (PROX-CO). We show that at 350 °C the carbon matrix was already mostly burnt and that higher temperatures and holding times mostly increase the CeO2 crystallite sizes. The sample prepared at 350 °C presented the highest surface area, 106 m2 ·g-1, in comparison to 60-70 m2 ·g-1 obtained for all other conditions. Transmission electron microscopy images of the catalyst calcined at 600 °C for 6 h showed 200 nm spheres formed by aggregation of ceria crystallites with crystalline domains of about 20 nm. All samples showed similar catalytic activity in PROX-CO indicating that the creation of the catalytic sites were mostly determined during the synthesis conditions and the catalytic performance were not deeply affected by the differences on CeOx matrix.

Redox and Catalytic Properties of RhxCe1–xO2−δ Solid Solution

In this work, a detailed study of the redox properties of solid solution RhxCe1–xO2−δ in correlation with its catalytic activity in CO oxidation reaction was carried out. The ex situ X-ray photoelectron spectroscopy technique was applied to follow the charging states of the elements on the surface during the redox treatments at a temperature range of 25–450 °C. The results were compared with the data of temperature-programmed reduction by CO. The dissolution of rhodium in the ceria bulk considerably increased the mobility of CeO2 lattice oxygen, with redox transitions Ce4+ ↔ Ce3+ and Rh3+ ↔ Rhnδ+ observed already at low temperatures (below 150 °C). The reduced rhodium clusters (Rhnδ+) formed during the reduction treatment significantly improved the catalytic activity of the RhxCe1–xO2−δ solid solution. The small size of the rhodium clusters (Rhnδ+) and high defectiveness of the fluorite phase provided the reversibility of Rhnδ+/CeO2 ↔ RhxCe1–xO2−δ transitions upon redox treatment, resulting in the high re...

A strawsheave-like metal organic framework Ce-BTC derivative containing high specific surface area for improving the catalytic activity of CO oxidation reaction

A metal organic framework Ce-BTC derivative with a special morphology and a large surface area was prepared by a simple method. Several analytical tools such as scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR), N2 adsorption-desorption (BET), H2 temperature programmed reduction (H2-TPR), ultraviolet visible diffuse reflectance spectrum (UV-Vis DRS), photoluminescence (PL), X-ray photoelectron spectroscopic (XPS) and elemental analysis (EA) have been used to characterize the samples. It is found that Ce-BTC calcined with O2 at 250 °C (Ce-BTC250) maintains the special strawsheave-like structure, and the surface area rapidly increases from 42 m2 g-1 to 648 m2 g-1. Moreover, the prepared strawsheave-like Ce-BTC250 exhibited excellent catalytic activity, long-term stability and water resistance. Further studies have shown that the MOF structure of Ce-BTC250 was gradually converted to carbon-free CeO2 during the catalytic reaction. Interestingly, the catalyst after the reaction still has a large surface area (124 m2 g-1) and the strawsheave-like morphology. The improved catalytic activities may be due to the formation of porous and large surface area of strawsheave-like Ce-BTC derivative, which provided more active sites and oxygen vacancy for CO oxidation. This work provides a novel sight for preparing high efficient carbon-free derivative with large surface area by controlling synthesis and reaction conditions of Ce based MOF.

Effect of SO2 on Catalytic CO Oxidation Over Nano-Structured, Mesoporous Au/Ce1−xZrxO2 Catalysts

A series of nano-structured, mesoporous Au/Ce1 − xZrxO2 type catalysts were synthesized by first synthesizing Ce1−xZrxO2 type of support with different degree of Zr substitutions and following sol–gel route. One weight percent of Au was incorporated on these supports using deposition–precipitation method. These synthesized catalysts were characterized in detail by various techniques, and evaluated for their CO oxidation activity. Effect of SO2 poisoning on catalytic CO oxidation activity was also investigated in detail. It was observed that the catalytic activity for CO oxidation reaction depends on the Ce/Zr molar ratio. The effect of SO2 on CO oxidation was less prominent for the Zr incorporated ‘Au/Ce0.8Zr0.2O2 (ACZ0.2)’ as compared to bare ‘Au/CeO2 (AC)’ catalyst. In case of ACZ0.2, the activity remains quite stable even after 5 h of SO2 exposure, however, after 12 and 18 h, the activity decreases to 62 and 55%, respectively. Whereas AC catalyst shows rapid decline in catalytic activity from the first hour of SO2 exposure, and continue to decline significantly to 35 and 18% after 12 and 18 h of SO2 exposure, respectively. Multiple regeneration studies of both bare and Zr incorporated catalysts show pronounced improvement/regain in catalytic activity.

Copper-ceria sheets catalysts: Effect of copper species on catalytic activity in CO oxidation reaction

Copper-ceria sheets catalysts with different loadings of copper (2 wt.%, 5 wt.% and 10 wt.%) supported on ceria nanosheets were synthesized via a deposition–precipitation (DP) method. The prepared catalysts were systematically characterized with various structural and textural detections including X-ray diffraction (XRD), Raman spectra, transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), and temperature-programmed reduction by hydrogen (H2-TPR), and tested for the CO oxidation reaction. Notably, the sample containing 5 wt.% of Cu exhibited the best catalytic performance as a result of the highest number of active CuO species on the catalyst surface. Further increase of copper content strongly affects the dispersion of copper and thus leads to the formation of less active bulk CuO phase, which was verified by XRD and H2-TPR analysis. Moreover, on the basis of in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) results, the surface Cu+ species, which are derived from the reduction of Cu2+, are likely to play a crucial role in the catalyzing CO oxidation. Consequently, the superior catalytic performance of the copper-ceria sheets is mainly attributed to the highly dispersed CuOx cluster rather than Cu-[Ox]-Ce structure, while the bulk CuO phase is adverse to the catalytic activity of CO oxidation.

Preparation of cerium doped Cu/MIL-53(Al) catalyst and its catalytic activity in CO oxidation reaction

Metal-organic framework (MOF) material MIL-53(Al) with high thermal stability was prepared by a solvothermal method, serving as a support material of cerium doped copper catalyst (Ce-Cu)/MIL-53(Al) material for CO oxidation with high catalytic activity. The catalytic performance between the (Cu-Ce)/MIL-53(Al) and the Cu/MIL-53(Al) catalytic material was compared to understand the catalytic behavior of the catalysts. The catalysts were characterized by thermogravimetric-differential scanning calorimetry (TG-DSC), N2 adsorption- desorption, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The characterization results showed that MIL-53(Al) had good stability and high surface areas, the (Ce-Cu) nanoparticles on the MIL-53(Al) support was uniform. Therefore, the heterogeneous catalytic composite materials (Ce-Cu)/MIL-53(Al) catalyst exhibited much higher activity than that of the Cu/MIL- 53(Al) catalyst in CO oxidation test, with 100% conversion at 80 °C. The results reveal that (Cu-Ce)/MIL- 53(Al) is the suitable candidate for achieving low temperature and higher activity CO oxidation catalyst of MOFs.

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.

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.

Simple preparation of crystal Co3(BTC)2·12H2O and its catalytic activity in CO oxidation reaction

Crystalline metal-organic framework cobalt (II) benzenetricarboxylate Co3(BTC)2·12H2O (MOF-Co) has been prepared using solvothermal method. The reaction of cobalt (II) nitrate and 1,3,5-benzenetricarboxylic (BTC) acid in a mixed solution of N,N-dimethylformamide (DMF)/C2H5OH/H2O (1:1:1, v/v) at low temperature for short reaction times produced this crystalline compound. Compared with traditional hydrothermal method, a mixed solution method for the synthesis of crystalline metal complex was found to be highly efficient. After water molecules were removed from this metal complex, its exposed nodes served as active sites. When this MOF-Co was employed in the oxidation of CO, it showed good catalytic properties causing 100% conversion of CO to CO2 at low temperature of 160 °C.