Activity For Carbon Monoxide Oxidation Research Articles

Improved Catalytic Performance of Au/α-Fe2O3-Like-Worm Catalyst for Low Temperature CO Oxidation.

The gold catalysts supported on various morphologies of α-Fe2O3 in carbon monoxide (CO) oxidation reaction have been studied for many researchers. However, how to improve the catalytic activity and thermal stability for CO oxidation is still important. In this work, an unusual morphology of α-Fe2O3 was prepared by hydrothermal method and gold nanoparticles were supported using a deposition-precipitation method. Au/α-Fe2O3 catalyst exhibited great activity for CO oxidation. The crystal structure and microstructure images of α-Fe2O3 were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the size of gold nanoparticles was determined by transmission electron microscopy (TEM). X-ray photoelectron spectra (XPS) and Fourier transform infrared spectra (FTIR) results confirmed that the state of gold was metallic. The 1.86% Au/α-Fe2O3 catalyst calcined at 300 °C had the best catalytic performance for CO oxidation reaction and the mechanism for CO oxidation reaction was also discussed. It is highly likely that the small size of gold nanoparticle, oxygen vacancies and active sites played the decisive roles in CO oxidation reaction.

In operando studies of CO oxidation on epitaxial SrCoO2.5+δ thin films

The high abundance and fast kinetics of select transition metal oxide catalysts are attractive features for many chemical and electrochemical device applications. However, the activity of such catalysts can be accompanied by phase instabilities that prevent their widespread usage. Furthermore, complexities associated with variations in phase behavior and oxygen stoichiometry have hindered studies on the true origins of catalytic activity. Here, we explore the interactions between activity, phase stability, and microstructure using in operando synchrotron X-ray techniques and gas chromatography/mass spectroscopy (GCMS) to probe the behavior of model SrCoO2.5+δ (SCO) catalysts. Pulsed laser deposition was used to prepare SCO thin films on (001) SrTiO3, (111) SrTiO3, and pseudocubic (001) DyScO3 substrates. The GCMS catalytic measurements were performed with a custom-built microreactor compatible with a synchrotron X-ray diffractometer at the Advanced Photon Source. The activity for carbon monoxide oxidation was determined as a function of temperature from 500 °C to 800 °C. We show that the SrCoO2.5+δ films are active for CO oxidation, most likely by direct reaction with lattice oxygen; consequently, the activity was observed to increase as the films become less stable, with the most active film being the one exhibiting the lowest surface and crystal quality. All films decompose at high temperatures, with in operando diffraction indicating the gradual formation of Sr-rich hexagonal and CoO phases. We find that real-time studies of model oxide systems with synchrotron X-rays is a powerful means of gaining insight into the varied processes taking place at catalytic surfaces.

Solid-state CTAB-assisted synthesis of mesoporous Fe3O4 and Au@Fe3O4 by mechanochemistry

Mesoporous iron oxides have shown excellent performance in many research areas such as catalysts, biosensors, enzyme immobilization, heavy metal adsorption, and drug delivery. The state-of-the-art synthesis methods are mostly wet chemistry processes. This paper reports a solvent-free approach for the rapid synthesis of mesoporous Fe3O4 (specific surface area up to 170 m2/g) and Au@Fe3O4 (highly dispersed Au nanoparticles, average particle size: ∼4 nm). With different amounts of added template agent, cetyltrimethylammonium bromide (CTAB), the pore structure could easily be adjusted. More importantly, the mesoporous Fe3O4 exhibited good catalytic activity in carbon monoxide (CO) oxidation, outperforming commercially purchased Fe3O4 with 100% CO conversion at around 274 °C vs. 490 °C for the commercial product.

Microwave-assisted integration of transition metal oxide nanocoatings on manganese oxide nanoarray monoliths for low temperature CO oxidation

Manganese oxide (OMS-2), a promising exhaust treatment catalyst, has been successfully integrated onto the channel wall surfaces of cordierite honeycombs in the form of a nanoarray forest. To further improve their catalytic carbon monoxide (CO) oxidation activity, a series of different metal oxide nanocoatings were uniformly grown on the surface of OMS-2 nanoarrays by utilizing a facile and fast microwave-assisted synthesis method. The manganese-cobalt oxide core-shell nanoarray based monolithic catalysts exhibit the highest catalytic performance with a 100% CO conversion at 150 °C, in a sharp contrast with 325 °C for the bare OMS-2 nanoarrays. Different growth mechanisms of the layered Co(OH)2 and spinel Co3O4 induced by different cobalt precursors are used to explain the morphology evolution of the manganese-cobalt oxide core-shell nanoarrays. The Co3+ distributed on the surface of the nanoarrays acts as the active sites for CO oxidation. The small grain size, abundant surface-adsorbed oxygen, and interfacial effects between MnO2 and Co3O4 were found to favor the observed high catalytic activity. A thermal annealing study showed that high temperature induces the sintering of the nanoarray catalyst, which further affects the CO oxidation activity. This fast, cost-effective, and scalable method will provide a new route for synthesizing efficient core-shell nanoarray monolithic catalysts for low temperature catalysis.

Efficient CO (carbon monoxide) oxidation using gold catalysts supported on WO3/titanate protonated nanotubes

WO3/titanate protonated nanotubes used to disperse gold nanoparticles were prepared by the deposition-precipitation with urea method and tested in CO oxidation reaction. Remarkably enhanced CO oxidation activity was achieved with the addition of gold nanoparticles with respect to WO3/NT and Au/NT catalysts. XPS and H2/TPR showed that when the samples were activated at 400 °C under hydrogen treatment, gold was present in the metallic Au0 form and tungsten as W5+ and W6+ species; likewise, the addition of tungsten to the tubular morphology led to the formation of vacancies and new adsorption sites, preserving the structure at up to 400 °C. The interaction between WO3 and the titanate nanotubes was improved by adding gold nanoparticles with sizes around 1 and 3 nm under hydrogen treatment, increasing the content of reduced W5+ species that promoted the CO oxidation at low temperatures. The 2Au-3WO3/NT catalyst was active from 0 °C and showed temporary stability at room temperature.

Synthesis of silver promoted CuMnOx catalyst for ambient temperature oxidation of carbon monoxide

Abstract The present research shows that the addition of silver (Ag), by the deposition-precipitation method, to a mixed CuMnOx catalyst can improve the activity of carbon monoxide (CO) oxidation. The CuMnOx catalyst doped with 3 wt.% Ag shows a higher catalytic activity as compared to the 1, 2, 4 and 5 wt.% Ag doped samples. The loading of Ag could introduce new active sites into the CuMnOx catalyst and reduce its deactivation. The order of the optimal calcination strategies based on the performance of catalysts for CO oxidation is as follows: Reactive Calcination > Flowing air > Stagnant air. All the catalysts were characterized by XRD, FTIR, BET, XPS and SEM-EDX techniques. It was found that the high active surface area was one of the main factors for the high catalytic activity of the Ag-promoted CuMnOx catalyst.

Unraveling template-free fabrication of carbon nitride nanorods codoped with Pt and Pd for efficient electrochemical and photoelectrochemical carbon monoxide oxidation at room temperature.

The tailored synthesis of carbon nitrides (CNs) is of particular interest in multidisciplinary catalytic applications. However, their fabrication in the form of one-dimensional (1D) nanorods for electrocatalytic carbon monoxide (CO) oxidation is not hitherto reported. Herein, a facile roadmap is presented for the rational design of Pt- and Pd-codoped CN (PtPd/CNs) nanorods via protonation of melamine in an ethylene glycol solution containing Pt and Pd precursors using NaNO3 and HCl and subsequent annealing. The protonation induces the polymerization of melamine to melon nanosheets that consequently roll up to CN nanorods. This tailored the prompt high mass production of uniform 1D CN nanorods (94 ± 2 nm) with a high surface area (155.2 m2 g-1) and they were atomically codoped with Pt and Pd (1.5 wt%) without a template and/or multiple complicated steps. The electrocatalytic CO oxidation activity of PtPd/CNs is 2.01 and 23.41 times greater than that of the commercial Pt/C catalyst and metal-free CNs, respectively, at room temperature. Meanwhile, the UV-vis light irradiation enhanced the CO oxidation activity of PtPd/CNs nanorods by 1.48 fold compared to that in the dark, emanated from the coupling between the drastic inbuilt catalytic merits of PtPd and the inimitable physicochemical properties of CNs. The presented study may pave the way for using CN-based materials in gas conversion reactions.

A CO Adsorption Site Change Induced by Copper Substitution in a Ruthenium Catalyst for Enhanced CO Oxidation Activity

AbstractRu is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance‐improved and cost‐reduced solid‐solution alloy nanoparticles of the Cu‐Ru system for CO oxidation are now presented. Over the whole composition range, all of the CuxRu1−x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations.

Interface Engineering of Gold Nanoclusters for CO Oxidation Catalysis.

Catalysts based on atomically precise gold nanoclusters serve as an ideal model to relate the catalytic activity to the geometrical and electronic structures as well as the ligand effect. Herein, we investigate three series of ligand (thiolate)-protected gold nanoclusters, including Au38(SR)24, Au36(SR')24, and Au25(SR″)18, with a focus on their interface effects using carbon monoxide (CO) oxidation as a probe reaction. The first comparison is within each series, which reveals the same trend for the three series that, rather than the bulkiness of carbon tails as commonly thought, the steric hindrance of ligands at the interface between the thiolate, Au, and CeO2 inhibits CO adsorption onto Au sites and hence adversely affects the activity of CO oxidation. The second comparison is between the sets Au38(SR)24 and Au36(SR')24 of nearly the same size, which reveals that the Au36(SR')24 nanoclusters (with face centered cubic structure) are not sensitive to thermal pretreatment conditions, whereas the Au38(SR)24 catalysts (icosahedral structure) are and an optimum activity is observed at a pretreatment temperature of 150 °C. Overall, the atomically precise Au n(SR) m nanoclusters have revealed unprecedented details on the catalytic interface and atomic structure effects. It is hoped that such insights will benefit the ultimate goal of catalysis in future design of enzymelike catalysts for environmentally friendly green catalysis.

Atmospheric Pressure Oxygen Cold Plasma for Synthesizing Au/TiO2 Catalysts: Effect of Discharge Voltage and Discharge Time

Atmospheric pressure (AP) oxygen cold plasma was adopted to synthesize Au/TiO 2 catalysts with the assistance of a simple modified incipient wetness impregnation process. Discharge voltages of 25.0, 29.0, and 35.0 kV and discharge time of 1, 2, and 4 min are selected to investigate the effects of discharge voltage and discharge time on the property of the Au/TiO 2 catalysts. The results of carbon monoxide (CO) oxidation activity testing show that AP oxygen cold plasma is beneficial to enhance the activity of the Au/TiO 2 catalysts, and the optimal discharge voltage and time are 29.0 kV and 1 min, respectively. CO conversion of the Au/TiO2-29-1 catalyst at 30 °C is 1.42 times as that of the Au/TiO 2 -As catalyst without plasma treatment. The UV-Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy characterizations indicate that AP oxygen cold plasma not only can decompose the gold species formed by the modified impregnation process to form metallic gold species but also can remove some of the oxygen species on the surface of the TiO 2 support. The discharge time of 1 min at 29.0 kV is enough to decompose the gold species formed by the modified impregnation process, and to keep much active hydroxyl groups. Moreover, there is little difference in the size of gold nanoparticles in the Au/TiO 2 catalysts. Therefore, Au/TiO2-29-1 catalyst exhibits higher CO oxidation activity than Au/TiO 2 -As, and 1 min is the optimal discharge time. Thanks to the AP oxygen cold plasma method, high-performance Au/TiO 2 catalysts can be synthesized simply in a short time.

Effect of various metal oxides phases present in CuMnOx catalyst for selective CO oxidation

Hopcalite (CuMnOx) is a highly efficient catalyst for low temperature oxidation of Carbon monoxide (CO). As synthesized by Co-precipitation method, it shows the high activity for CO oxidation. The coordination between CuO and MnOx in CuMnOx catalyst improves the catalytic activity for CO oxidation. In this research work, we investigate the individual catalytic activity of CuO and MnOx and compare with the multiphase CuMnOx catalyst. The performance of multiphase catalysts CuO and MnO2 were numerous times higher as compared to single phase CuMnOx. The activity order of catalysts for CO oxidation was as follows: CuMnOx> MnOx > CuOx. The success of CuMnOx catalyst has prompted a great deal of research work into each component and nature of active sites. In CuMnOx catalyst, the MnOx acts as an oxygen donor and CuO acts as an oxygen acceptor. The presence of MnOx is possible to assist in the reduction of CuO, due to the coordination between CuO and MnOx. The calcination strategies of precursors highly affect the physicochemical and catalytic properties of the catalysts for CO oxidation. The reactive calcination (RC) conditions (4.5% CO in air) for prepared catalysts showed the best activity result for CO oxidation, as compared to the traditional method of calcination.

Electro-oxidation of Glycerol on Carbon Supported Pt75CoxNi25-x (x = 0, 0.9, 12.5, 24.1 and 25) Catalysts in an Alkaline Medium

Binary and ternary Pt75CoxNi25-x/C (x = 0, 0.9, 12.5, 24.1, and 25) electrocatalysts were prepared by a polyol method, and their activity for carbon monoxide and glycerol oxidation in alkaline media was compared to that of a conventional Pt/C catalyst. Formation of partially alloyed catalysts was detected by XRD analysis, with the most part of the non-precious metals in a non-alloyed form. The onset potential for carbon monoxide and glycerol oxidation on binary and ternary Pt75CoxNi25-x/C catalysts was lower than that on Pt/C. The higher activity for glycerol oxidation of the Pt75Co0.9Ni24.1/C and Pt75Co12.5Ni12.5/C catalysts than that of the parent binary catalysts was ascribed to the formation of highly active CoxNi1-x(OH)2/CoxNi1-xOOH redox couples with a Co/Ni atomic ratio ≤ 1. Conversely, the replacement of a small amount of Co (0.9 at.%) by Ni did not increase the glycerol oxidation activity of the resulting Pt75Co24.1Ni0.9/C catalyst. The higher activity for glycerol oxidation of Pt75Co12.5Ni12.5/C than that of Pt75Co0.9Ni24.1/C for potentials > 0.7 V vs. RHE, despite the lower Ni-based oxide content and the higher particle size, indicated that at these potentials, the Co12.5Ni12.5(OH)2/Co12.5Ni12.5OOH redox couple is more active for glycerol oxidation than the Co0.9Ni24.1/Co0.9Ni24.1OOH redox couple.

Hollow and Core–Shell Nanostructure Co3O4 Derived from a Metal Formate Framework toward High Catalytic Activity of CO Oxidation

Hollow and core–shell particles are currently attracting global attention because of their special properties. We herein proposed a facile self-sacrificial template strategy for the synthesis of cobalt tetraoxide (Co3O4) with hollow and core–shell nanostructures. Starting with metal formate framework (MFF) template [CH3NH3][Co(HCOO)3], a series of core–shell nanostructure MFF@Co(OH)2 microboxes and hollow Co(OH)2-H were successfully obtained through a reaction between the MFF template and sodium hydroxide (NaOH) combined with different washing processes. Finally, hollow and core–shell nanostructure Co3O4 products were obtained after calcination, which inherited the structures from corresponding precursors. In addition, the formation processes of hollow and core–shell nanostructures were studied. Moreover, the catalytic activity of the as-obtained Co3O4 for carbon monoxide (CO) oxidation was investigated. Such hollow and core–shell nanostructures gave different physiochemical properties. Hollow structure C...

Ordered intermetallic Pt-Fe nano-catalysts for carbon monoxide and benzene oxidation

Conversion of toxic, indoor pollutants into innocuous products through catalytic reaction is one of the promising among other permanent solutions. γ-Al2O3 supported, Pt-based intermetallic nanoparticles (NPs) using abundantly available metal e.g., Fe (Pt-Fe; Pt3Fe and PtFe3) as catalysts are successfully prepared through a wet-impregnation method followed by calcination in the presence of H2 at 800 °C. Although the intermetallic Pt-Fe NPs are prepared at elevated temperatures, they are, however, not agglomerated and are finely dispersed on the γ-Al2O3 support with the average particle size between 4 and 6 nm. No other intermetallic or alloy phases of Pt-Fe were not observed under the set synthesis conditions. Despite the same Pt-mass loading in the both Pt-Fe catalysts, intermetallic PtFe3 catalysts showed much improved carbon monoxide (CO) oxidation activity by at least 8-fold compared to that of the intermetallic Pt3Fe catalysts. The intermetallic PtFe3 catalysts showed the enhanced activity for CO oxidation compared to that of the intermetallic Pt3Fe catalysts, however, both the intermetallic Pt-Fe catalysts showed virtually the same catalytic activity for benzene oxidation. Both the intermetallic Pt-Fe catalysts showed the stable, multi-cycle catalytic performance for the catalytic CO and benzene oxidation and retain their structure and morphology even after catalytic reaction.

Activation of surface lattice oxygen in single-atom Pt/CeO2 for low-temperature CO oxidation.

To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of heat wasted in the exhaust. Hence, future generations of catalysts must perform at temperatures that are 100°C lower than current exhaust-treatment catalysts. Achieving low-temperature activity, while surviving the harsh conditions encountered at high engine loads, remains a formidable challenge. In this study, we demonstrate how atomically dispersed ionic platinum (Pt2+) on ceria (CeO2), which is already thermally stable, can be activated via steam treatment (at 750°C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability. A new type of active site is created on CeO2 in the vicinity of Pt2+, which provides the improved reactivity. These active sites are stable up to 800°C in oxidizing environments.

High Surface Area M (M = La, Pr, Nd, and Pm)-Doped Ceria Nanoparticles: Synthesis, Characterization, and Activity Comparison for CO Oxidation

High surface area M (M = La, Pr, Nd, and Pm)-doped ceria nanoparticles have been synthesized by the citric acid-aided sol–gel method to check their catalytic activity for carbon monoxide (CO) oxidation. BET analysis revealed high specific surface areas of M-doped CeO2 catalysts (∼190–198 m2 g–1). XRD and TEM showed 3–6 nm size of particles of M-doped CeO2 catalysts. Raman results showed the highest amount of oxygen vacancy possessed by La-doped CeO2 compared to other dopants. The catalytic activity for CO oxidation follows the order La-CeO2 > Pr-CeO2 > Nd-CeO2 > Pm-CeO2 > CeO2. La-doped CeO2 exhibited the highest catalytic activity (T50 - 170 °C) due to the higher quantity of oxygen vacancies, larger specific surface area, smaller particle size, and enhanced oxygen storage capacity (OSC) comparison to other dopants. This catalyst also showed an excellent stability for CO oxidation reaction for a time-on-stream of 50 h.

Ultrafast CO Kinetics in Heme Proteins: Adiabatic Ligand Binding and Heavy Atom Tunneling.

The ultrafast kinetics of CO rebinding to carbon monoxide oxidation activator protein (ChCooA) are measured over a wide temperature range and compared with the kinetics of CO binding in other heme systems such as myoglobin (Mb) and hemoglobin (Hb). The Arrhenius prefactor for CO binding to ChCooA and protoheme (∼1011 s-1) is similar to what is found for spin-allowed NO binding to heme proteins and is several orders of magnitude larger than the prefactor of Mb and Hb (∼109 s-1). This indicates that the CO binding reaction is adiabatic, in contrast to the commonly held view that it is nonadiabatic due to spin-forbidden (ΔS = 2) selection rules. Under the adiabatic condition, entropic factors, rather than spin-selection rules, are the source of the reduced Arrhenius prefactors associated with CO binding in Mb and Hb. The kinetic response of ChCooA-CO is nonexponential at all temperatures, including 298 K, and is described quantitatively using a distribution of enthalpic rebinding barriers associated with heterogeneity in the heme doming conformation. Above the solvent glass transition (Tg ∼ 180 K), the rebinding progress slows as temperature increases, and this is ascribed to an evolution of the distribution toward increased heme doming and larger enthalpic barriers. Between Tg and ∼60 K, the nonexponential rebinding slows down as the temperature is lowered and the survival fraction follows the predictions expected for a quenched barrier distribution. Below ∼60 K the rebinding kinetics do not follow these predictions unless quantum mechanical tunneling along the heme doming coordinate is also included as an active channel for CO binding.

Low-temperature CO oxidation over Cu/Pt co-doped ZrO2 nanoparticles synthesized by solution combustion.

Zirconia (ZrO2) nanoparticles co-doped with Cu and Pt were applied as catalysts for carbon monoxide (CO) oxidation. These materials were prepared through solution combustion in order to obtain highly active and stable catalytic nanomaterials. This method allows Pt2+ and Cu2+ ions to dissolve into the ZrO2 lattice and thus creates oxygen vacancies due to lattice distortion and charge imbalance. High-resolution transmission electron microscopy (HRTEM) results showed Cu/Pt co-doped ZrO2 nanoparticles with a size of ca. 10 nm. X-ray diffraction (XRD) and Raman spectra confirmed cubic structure and larger oxygen vacancies. The nanoparticles showed excellent activity for CO oxidation. The temperature T50 (the temperature at which 50% of CO are converted) was lowered by 175 °C in comparison to bare ZrO2. Further, they exhibited very high stability for CO reaction (time-on-stream ≈ 70 h). This is due to combined effect of smaller particle size, large oxygen vacancies, high specific surface area and better thermal stability of the Cu/Pt co-doped ZrO2 nanoparticles. The apparent activation energy for CO oxidation is found to be 45.6 kJ·mol−1. The CO conversion decreases with increase in gas hourly space velocity (GHSV) and initial CO concentration.

Parametric Studies of Titania-Supported Gold-Catalyzed Oxidation of Carbon Monoxide.

This paper remarks the general correlations of the shape and crystallinity of titanium dioxide (TiO2) support on gold deposition and carbon monoxide (CO) oxidation. It was found that due to the larger rutile TiO2 particles and thus the pore volume, the deposited gold particles tended to agglomerate, resulting in smaller catalyst surface area and limited gold loading, whilst anatase TiO2 enabled better gold deposition. Those properties directly related to gold particle size and thus the number of low coordinated atoms play dominant roles in enhancing CO oxidation activity. Gold deposited on anatase spheroidal TiO2 at photo-deposition wavelength of 410 nm for 5 min resulted in the highest CO oxidation activity of 0.0617 mmol CO/s.gAu (89.5% conversion) due to the comparatively highest catalyst surface area (114.4 m2/g), smallest gold particle size (2.8 nm), highest gold loading (7.2%), and highest Au0 content (68 mg/g catalyst). CO oxidation activity was also found to be directly proportional to the Au0 content. Based on diffuse reflectance infrared Fourier transform spectroscopy, we postulate that anatase TiO2-supported Au undergoes rapid direct oxidation whilst CO oxidation on rutile TiO2-supported Au could be inhibited by co-adsorption of oxygen.

Kinetics of catalytic oxidation of carbon monoxide over CuMnAgOx catalyst

The CuMnAgOx catalyst was prepared by the deposition-precipitation method and followed by calcination at 300°C, which showed excellent activity and stability for carbon monoxide (CO) oxidation at low temperature. This paper describes the kinetics of catalytic air oxidation of CO over the CuMnAgOx catalyst and their kinetics data were collected in a plug flow tubular reactor. The data were collected under the following reaction conditions: 100mg catalyst, 2.5% CO in air, total flow rate maintained 60ml/min and temperature range 25–30°C. The CO oxidation followed in a different reaction mechanism at a broad range of experimental temperature. A better tool for measuring the performance of CuMnAgOx catalyst for CO oxidation is the activation energy for the process and it’s used for the modeling and design of the catalytic converter. The data were fitted into the power law rate equation. The frequency factor and activation energy were found to be 2.7790×105 (gmol)/(gcath) and 16.977kJ/gmol, respectively.