Catalytic Activity For CO Oxidation Research Articles

An activity descriptor for perovskite oxides in catalysis

Perovskite oxides are a class of important metal oxide catalysts, the activities of which are explained largely by the delocalized band descriptor and the local orbital descriptor that are fundamentally debated. We solve this dispute by proposing a frontier band orbital descriptor that rationalizes catalytic activity trends over a series of perovskite oxides. The descriptor is defined as the energy difference (Δε) between the highest occupied band orbital and the lowest unoccupied band orbital, as determined by using valence-band X-ray photoelectron spectroscopy and O K-edge X-ray absorption spectroscopy, respectively. Catalytic activity in CO or NO oxidation increases linearly as Δε value decreases, evidencing the validity of the descriptor. Owing to the frontier orbitals of catalytic sites being endowed with characteristics of delocalized bands of entire catalysts, this descriptor gives unified explanations to disparate reported results, providing a promising strategy for designing optimal semiconducting metal oxide catalysts, particularly for perovskite catalysts.

Effect of one-dimensional ceria morphology on CuO/CeO2 catalysts for CO preferential oxidation

The one-dimensional CeO2 nanocrystals (nanorods, nanowires and nanotubes) were synthesized by hydrothermal methods and supported CuO for CO preferential oxidation (CO-PROX). The supports and catalysts were characterized by various techniques. The results show that the morphologies of support and the interaction between copper species and ceria greatly affect the activity of catalysts. Compared with CeO2-W and CeO2-R, CeO2-T presents higher activity at low-temperature. After loading CuO, the strong interaction between CuO and CeO2 nanocrystals makes the activity of CuCeO catalysts much higher than that of CeO2. Among the CuCeO catalysts, CuCeO-T displays the best catalytic activity for CO oxidation. The CO conversion over CuCeO-T can reach to 100% at 100 ​°C with O2 selectivity of 89%. The addition of copper species further enriches the surface defects, Ce3+ concentration and oxygen vacancies, which should be the main reason for the high activity of CuCeO-T catalyst.

Effect of poly(N-vinylpyrrolidone) ligand on catalytic activities of Au nanoparticles supported on Nb2O5 for CO oxidation and furfural oxidation

The development of green preparation methods for acidic metal oxide supported gold catalysts is of great importance for the extensive use of gold catalysts as well as for a comprehensive understanding of gold catalysts. In this study, poly(N-vinylpyrrolidone) (PVP) was used as the stabilizer of gold colloids to deposit gold nanoparticles on an acidic metal oxide, Nb2O5. The effects of the PVP ligand on the preparation of Au(-PVP)/Nb2O5 and on the catalytic activities for gas-phase CO oxidation and liquid-phase furfural oxidation were investigated. As removing more ligand PVP of Au(-PVP)/Nb2O5, the catalytic activities for both CO oxidation and furfural oxidation increased. The optimal calcination temperature for Au(-PVP)/Nb2O5 was determined to be 400 °C, and calcination at that temperature gave gold nanoparticles with an average size of 6.4 ± 2.5 nm and of the support of Nb2O5 remained as the original crystalline structure. The temperature for 50% CO conversion (T50%) of Au(-PVP)/Nb2O5 (calcined at 400 °C) was 81 °C. In addition, Au(-PVP)/Nb2O5 (calcined at 400 °C) presented 43% furfural conversion with 100% selectivity of furoic acid under a mild conditions (0.5 MPa O2, 40 °C) in the batch system. These results suggested that Au(-PVP)/Nb2O5 is a good catalyst for both gas-phase and liquid-phase reactions.

Efficient non-volatile organogold complex for TiO2-supported gold cluster catalysts: Preparation and catalytic activity for CO oxidation

Gold nanoparticles supported on titania (Au/TiO2) catalysts were prepared by solid grinding (SG) method using a halide-free nonvolatile organogold complex, bis(phenyl)boroxinato(4-tolylpyridyl)gold(III), abbreviated as AuBO, followed by calcination. Density functional theory (DFT) calculation revealed that AuBO was adsorbed on TiO2 by hydrogen bonding with the surface hydroxy group of TiO2 and that the adsorption energy was lower than those of other gold precursors. The obtained catalyst (AuBO/TiO2) showed higher catalytic activity for CO oxidation than did Au/TiO2 prepared by conventional deposition–precipitation method and by SG using other organogold complexes. Furthermore, grinding of the gold precursor with potassium tert-butoxide followed by calcination (AuBO/K-TiO2) improved the catalytic activity and 100% CO conversion reached at − 23 °C (temperature at which 50% CO conversion occurs, T1/2 = − 39 °C) as compared to AuBO/TiO2 (T1/2 = − 28 °C). Potassium tert-butoxide facilitated the decomposition of AuBO adsorbed on TiO2, and increased surface basicity contributed to the improved catalytic activity. AuBO/K-TiO2 also exhibited high catalyst stability for CO oxidation at room temperature.

The activation of MnOx-ZrO2 catalyst in CO oxidation: Operando XRD study

The present study demonstrates that the reduction–oxidation pretreatment leads to an increase in the catalytic activity in CO oxidation for MnOx-ZrO2 catalyst. Crystalline phases present in as-prepared MnOx-ZrO2 catalyst are Mn3O4, Mn2O3 and solid solution (Mn,Zr)O2. By varying the conditions of pretreatment, the following results can be achieved: (1) decomposition of a solid solution; (2) change the ratio and the dispersion of oxides. In CO environment, the reduction of Mn cations occurs both in the volume of the (Mn,Zr)O2 solid solution and in manganese oxides. The reduction process is accompanied by the MnO segregation on the surface of the initial oxides. In an oxygen-containing environment, the reoxidation of surface manganese oxides proceeds with the formation of Mn2O3 and Mn3O4.

Theoretical studies of MXene-supported single-atom catalysts: Os1/Ti2CS2 for low-temperature CO oxidation

We report herein a new sulfur-functionalized MXene Ti2C (Ti2CS2)-supported osmium-metal single-atom catalyst (SAC) Os1/Ti2CS2 with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os1/Ti2CS2, has been screened from a series of group 8–11 transition metal SACs M1/Ti2CS2 (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Pt, Au). The calculations show that it is favorable for O2 and CO to be coadsorbed on the Os1 single atom (SA) of Os1/Ti2CS2 and the adsorption energy of the first O2 molecule is slightly higher than that of CO. Moreover, the termolecular co-adsorption of O2 + 2CO on Os1 SA is also possible, which is favorable for CO oxidation on Os1 SA through a novel three-molecule reaction mechanism. Accordingly, four different catalytic mechanisms, the Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R), termolecular Langmuir-Hinshelwood-A (TLH-A) and termolecular Langmuir-Hinshelwood-B (TLH-B), are systematically studied for CO oxidation by O2 on Os1/Ti2CS2. The theoretical studies indicate that the TLH-B mechanism is the most feasible for CO oxidation with the reaction barrier energy of only 0.74 eV, which is far lower than for L-H, E-R and TLH-A with barrier energies of 1.06, 1.09 and 1.47 eV, respectively. The results provide fundamental understanding to the surface chemistry of MXene and designing new sulfur-functionalized two-dimensional MXene catalytic nanomaterials.

CO Oxidation Activity of Au on Spinel Titanate Supports: Improvement of Catalytic Activity via Alkali Cation Substitution from Li4Ti5O12 to Na3LiTi5O12

Abstract In this study, density functional theory calculations determined that the formation of O vacancies in spinel-type titanium oxide is affected by the alkali metal cation occupying the 8a-site. This result indicates that substitution of the 8a-site cation, such as Li+→Na+, should improve catalytic oxidation activity. Experimental results confirmed that Au supported on sodium titanate (Na3LiTi5O12) showed improved catalytic CO oxidation activity compared to Au supported on lithium titanate (Li4Ti5O12).

Facile synthesis of Co3O4@SiO2/Carbon Nanocomposite Catalysts from Rice Husk for Low-Temperature CO Oxidation

Co3O4 was synthesized in the presence of 3D porous nanostructured SiO2/carbon composite derived from rice husk via a hydrothermal method to produce Co3O4@SiO2/C nanostructures with good microstructural, morphological and excelling catalytic properties. The morphology and textural properties of the products were tuned by using different amounts of hydrocarbonized rice husk. TEM images exhibited nanoclusters 1–9 nm in diameter and reducing the nanoparticle size of Co3O4 by adding hydrocarbonized rice husk. The specific surface area value of Co3O4@SiO2/C is 115 m2 /g which is significantly improved as compared to Co3O4 prepared in the absence of hydrocarbonized rice husk (70 m2 /g). Materials were tested in the oxidation of CO oxidation as model reaction. Compared to conventional Co3O4 nanoparticles, as-prepared Co3O4@SiO2/C exhibited a superior catalytic activity for CO oxidation, i.e., T50 (50% conversion) is at <25 °C (at 100°C for Co3O4).

Impact of iso/aliovalent dopants in ceria solid solutions for improved CO oxidation

Ceria based solid solution (Cu0.08Mn0.02MxCe0.9-xO2) were synthesized by the co-precipitation method, followed by calcination at the temperature of 500°С. These catalysts were examined for low-temperature oxidation of CO. A small content of iso/aliovalent dopants (Bi, Ti, Sn) resulted in an increase of the catalytic activity in CO oxidation. The addition of the dopant leads to a positive effect, while a further increase of its concentration leads to a decrease in activity possibly due to the “dilution” of the active surface with less active catalytic centers (Sn, Ti, and Bi replace Cu and Mn). CO is adsorbed on the Cu+, Mn2+, Mn3+, Sn2+ surface sites and directly oxidized by the oxygen species activated on the oxygen vacancies of ceria solid solution from the molecular oxygen in the reaction gas, so the activity for CO oxidation may be correlated with the concentration of these sites and oxygen vacancies.

Nanostructured ceria-based catalysts doped with La and Nd: How acid-base sites and redox properties determine the oxidation mechanisms

In the present work, novel ceria-based nanocatalysts containing different quantities of La and Nd were prepared via hydrothermal synthesis. The effects of doping on the structural and physico-chemical properties of ceria were examined with several techniques, such as XRD, FESEM, TEM, Raman spectroscopy, XPS, H2-TPR and O2/NH3/CO2-TPD. The catalytic activity of doped ceria towards CO, NO and soot oxidation was evaluated in different conditions; in particular, the role of the catalyst-soot contact and the influence of NOx and water on the soot oxidation performances were investigated. La and Nd ions were well incorporated in ceria structure, but the final morphology was significantly altered. The introduction of trivalent cations was also associated with a higher abundance of defects and oxygen vacancies, but an excessive oxygen deficiency detrimentally affected the material reducibility and catalytic activity for CO and NO oxidation. Conversely, soot oxidation benefited from La and Nd addition. In particular, the Ce-La equimolar oxide exhibited outstanding performances in all the tested conditions, thanks to its optimal morphology and surface acidity. A detailed comparison with equimolar ceria-praseodymia allowed to investigate how acid-base sites and redox properties control the different catalytic mechanisms involved in standard and NOx-assisted soot oxidation.

Electrochemical Ce(III)/Ce(IV) interconversion, electrodeposition, and catalytic CO ↔ CO2 interconversion over terpyridine-modified indium tin oxide electrodes

Indium tin oxide (ITO) has extensively used as an electrode in diverse application areas of electrochemistry, displays, photovoltaics, and catalysts. Herein, terpyridine-modified ITO and thioterpyridine-functionalized Au-modified ITO electrodes were prepared and evaluated for electrochemical redox behaviors and conversion rates of Ce(III)/Ce(IV) ions, and recycling recovery rates on the newly developed electrode by cyclic voltammetry and amperometry. Scanning electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet photoelectron spectroscopy, X-ray diffraction crystallography, and fluorescence spectroscopy were employed for the physiochemical properties of the demonstrated electrodes before and after electrochemistry. The interfacial energy level was examined by ultraviolet photoelectron spectroscopy for ITO-Au and ITO-Au-STpy. Density functional theory calculations were performed to examine complexation between the functionalized ligand and Ce(III)/Ce(IV) ions by obtaining molecular orbital energy levels and thermodynamics. Thermal CO oxidation catalytic activity was tested for Ce-electrodeposited ITO electrode. In addition, electrochemical CO2 reduction performance was evaluated for Au-modified ITO electrode with and without thioterpyridine-functionalization.

Solution Combustion Synthesis of Nanostructured NiCr2O4 Spinel and Its Catalytic Activity in CO Oxidation

Solution Combustion Synthesis of Nanostructured NiCr2O4 Spinel and Its Catalytic Activity in CO Oxidation

Facile One-Step Flame Synthesis of La1−xSrxMnO3 Nanoparticles for CO Catalytic Oxidation

A large amount of CO as hazardous emission in the iron ore sintering process has caused severe harm to the environment and human health. To control the emission of CO more effectively, the preparation of highly efficient catalysts has attracted much attention. In this study, the La1-xSrxMnO3 (0 ≤ x &lt; 1) perovskite catalysts with different Sr2+ contents were prepared by the one-step flame synthesis method to treat CO pollutants in the iron and steel industry. The influence of Sr2+ doping on the structure and activity of catalytic were characterized and analyzed. La1-xSrxMnO3 perovskite catalysts exhibit good perovskite phases and loose spherical structures. The specific surface areas are between 4.1 and 12.0 m2 g−1. Combined with the results of H2-TPR and O2-TPD, the improvement of catalytic activity of La1-xSrxMnO3 perovskite can be attributed to the high concentration of active centers and oxygen vacancies. Significantly, the La0.4Sr0.6MnO3 catalyst presented the best reducibility and high content of absorbed active oxygen species, leading to a superior CO oxidation catalytic activity and reaches 50% CO conversion at 134.9°C and 90% at 163.2°C, respectively. The effects of water vapor and CO2 on the oxidation activity of La1-xSrxMnO3 perovskite was investigated. The flame-produced catalysts exhibit favorable catalytic stability and antisintering ability, achieving 100% CO conversion after fifth consecutive oxidation cycles.

Enhanced Catalytic Activity for CO Oxidation by Highly Active Pd Nanoparticles Supported on Reduced Graphene Oxide /Copper Metal Organic Framework

As a result of the increase in industrial activities and the extensive use of automobiles, air pollutants, especially carbon monoxide, reach the alarm level. The removal of carbon monoxide through oxidation is still one of the best tactics so far. Therefore, looking for an active and durable catalyst is considered the key factor for improving the oxidation process. In this work, Pd nanoparticles (1.0, 3.0 and 5.0 wt.%) were supported onto reduced graphene oxide / copper metal organic framework nanocomposite (rGO@Cu-BTC) through one pot solvothermal synthesis method. The catalysts were thoroughly characterized by state-of-the-art techniques such as XPS, SEM, TEM, XRD, N2 physisorption, and FT-IR. The results revealed that the Pd nanoparticles were exceptionally dispersed on rGO@Cu-BTC nanocomposite surface and the Cu-BTC crystals showed excellent octahedral structure with smooth edges as indicated SEM images. The results revealed that 3.0 wt. % Pd/rGO@Cu-BTC acts as an excellent catalyst in the CO oxidation as indicated by T50 and T100 values of 71 and 82 °C, respectively. Additionally, the results showed that rGO has a vital role in the dispersion of Pd NPs on the catalyst surface as well as the presence of surface oxygen groups, which yields higher catalytic activity compared with the catalyst without rGO.

A comparative study of CO catalytic oxidation on the single vacancy and di-vacancy graphene supported single-atom iridium catalysts: A DFT analysis

Engineering of high-performance catalysts is of great importance for reducing the greenhouse gas emission by the electrocatalytic oxidation of CO. Single-atom-catalysts (SACs) have gained substantial attention thanks to their superior catalytic activity for CO oxidation, and graphene has been considered as one most promising supporting material owing to its peculiar physicochemical properties. In this work, the mechanism of CO oxidation over iridium (Ir) embedded on both single vacancy graphene (Ir-GNSV) and di-vacancy graphene (Ir-GNDV) has been investigated with the aid of density functional theory (DFT). The structural properties of Ir-GNSV and Ir-GNDV were analyzed by Bader charge analysis and electron density difference map. The calculated adsorption energy values of CO and O2 molecules on both the Ir-GNSV and Ir-GNDV have validated that both molecules can be molecularly adsorbed on the surface of each catalyst at room temperature. The results put forth that the reaction mechanism of CO + O2 → OOCO → CO2 + O* prefers to Langmuir − Hinshelwood (LH) mechanism. The activation energy for the transition-state for Ir-GNSV has been calculated to be 0.31 eV, whereas the first transition state (TS1) and the second transition state (TS2) of Ir-GNDV have been determined as 0.30 eV and 0.26 eV, respectively. Moreover, the results have confirmed that Ir-GNSV and Ir-GNDV surfaces have high catalytic activity and selectivity towards CO oxidation. On the basis of these findings, the proposed Ir-GNSV and Ir-GNDV catalysts are considered to be promising SAC for CO oxidation at low-temperature. It can be speculated that this work paves the way for the engineering of boosted-performance Ir-based heterogeneous catalysts by providing deeper mechanistic insights.

Engineering Dual Active Sites at the Interface between Nanoporous Pt and Nanosized CeO2 to Enhance Photo‐Thermocatalytic CO Oxidation

AbstractEffective catalytic oxidation of toxic emissions at low temperatures has great significance on environmental protection. Herein, a novel structure of Pt/CeO2 catalyst, composed of abundant CeO2 clusters captured by nanoporous Pt particles, is designed to enhance the photo‐thermocatalytic CO oxidation by boosting the amount of active sites. The nanosized CeO2 support is fabricated by vacuum thermal decomposition and then the Pt/CeO2 catalyst with a nanoporous structure is synthesized by a one‐pot solution reduction method in a mild condition. The synthesized catalyst exhibits great low‐temperature CO catalytic oxidation activity, and the temperature for 90% CO conversion is 154 °C, achieving comparable catalytic activity with the single‐atom Pt/CeO2 catalyst. Abundant dual active sites, in terms of active oxygen absorbed on the oxygen vacancies and spillover from ceria to Pt, and active Pt sites located near the perimeter of the Pt–CeO2 interface, are formed to improve the photo‐thermocatalytic activity for CO oxidation.

An investigation on catalytic performance and reaction mechanisms of Fe/OMS-2 for the oxidation of carbon monoxide, ethyl acetate, and toluene

The octahedral molecular sieve (OMS-2)-supported Fe (xFe/OMS-2: x = 1, 3, 5, and 10) catalysts were prepared using the pre-incorporation method. Physicochemical properties of the as-synthesized materials were characterized by means of various techniques, and their catalytic activities for CO, ethyl acetate, and toluene oxidation were evaluated. Among all of the samples, performed the best, with the reaction temperature required to achieve 90% conversion (T90%) being 160°C for CO oxidation, 210°C for ethyl acetate oxidation, and 285°C for toluene oxidation. Such a good catalytic performance of 5Fe/OMS-2 was associated with its high (Mn3+ + Mn2+) content and adsorbed oxygen species concentration, and good low-temperature reducibility and lattice oxygen mobility as well as strong interaction between Fe and OMS-2. In addition, catalytic mechanisms of the oxidation of three pollutants over the 5Fe/OMS-2 catalyst were also studied. It was found that CO, ethyl acetate or toluene was first adsorbed, then the related intermediates were formed, and finally the formed intermediates were completely converted into CO2 and H2O.

Engineering Co3+-rich crystal planes on Co3O4 hexagonal nanosheets for CO and hydrocarbons oxidation with enhanced catalytic activity and water resistance

Crystal facet engineering plays a key role in the development of non-noble metal-based catalysts to be applicable in removal of atmospheric pollutants. Herein, we report a facile and effective reflux strategy for manipulating the exposed {112} crystal facets of Co3O4 hexagonal nanosheets with enhanced catalytic activity and water resistance for CO and hydrocarbons (methane and toluene) oxidation. Temperature-programmed techniques and density functional theory (DFT) calculations demonstrate the process that surface lattice oxygen on Co3O4 (112) activates the first C–H bond to form oxygen vacancies (1.84 eV) is easier than that (3.12 eV) on Co3O4 (111) while activation barrier (2.00 eV) on Co3O4 (112) from CO2 to bicarbonates is higher than that (0.60 eV) on Co3O4 (111), as a result of boosting catalytic oxidation and water resistance. The present work demonstrates that crystal facet engineering is a potential route to improve water resistance of Co3O4 catalysts with highly promising in practical application.

Catalytic oxidation of CO over Pt/TiO2 with low Pt loading: The effect of H2O and SO2

Anatase TiO2 loaded with 0.1wt.% Pt catalyst (0.1Pt/TiO2-A) was prepared via the impregnation method, and its CO catalytic oxidation activity was investigated. Noteworthy, introduction of H2O into the reaction atmosphere apparently facilitated the catalytic oxidation of CO. Besides, introduction of SO2 inhibited the catalytic oxidation of CO. In presence of H2O and SO2, 0.1Pt/TiO2-A showed outstanding catalytic stability, and X-ray photoelectron spectroscopy (XPS) and thermogravimetric (TG) characterizations suggested that the amount of sulfate species deposited on the 0.1Pt/TiO2-A treated at 230 °C did not increase with time extension, which might be an important reason for the high sulfur resistance of 0.1Pt/TiO2-A. XPS results also demonstrated that the dissociation of H2O led to considerably increase of hydroxyl groups over the catalyst surface. H218O isotope-labeling experiments unambiguously showed that C16O18O was the main product accounting for 88.9%, revealing that the other oxygen atom in the product CO2 was mostly from H2O. Consequently, based on previous researches and our experimental results, the mechanism of H2O promoting CO oxidation on 0.1Pt/TiO2-A catalyst was proposed.

Triazine COF-supported single-atom catalyst (Pd1/trzn-COF) for CO oxidation

Single-atom catalysts (SACs) with well-defined and specific single-atom dispersion on supports offer great potential for achieving both high catalytic activity and selectivity. Covalent organic frameworks (COFs) with tailor-made crystalline structures and designable atomic composition is a class of promising supports for SACs. Herein, we have studied the binding sites and stability of Pd single atoms (SAs) dispersed on triazine COF (Pd1/trzn-COF) and the reaction mechanism of CO oxidation using the density functional theory (DFT). By evaluating different adsorption sites, including the nucleophilic sp2 C atoms, heteroatoms and the conjugated π-electrons of aromatic ring and triazine, it is found that Pd SAs can stably combine with trzn-COF with a binding energy around −5.0 eV, and there are two co-existing dynamic Pd1/trzn-COFs due to the adjacent binding sites on trzn-COF. The reaction activities of CO oxidation on Pd1/trzn-COF can be regulated by the anion-π interaction between a + δ phenyl center and the related −δ moieties as well as the electron-withdrawing feature of imine in the specific complexes. The Pd1/trzn-COF catalyst is found to have a high catalytic activity for CO oxidation via a plausible tri-molecular Eley-Rideal (TER) reaction mechanism. This work provides insights into the d-π interaction between Pd SAs and trzn-COF, and helps to better understand and design new SACs supported on COF nanomaterials.