Complete Oxidation Of CO Research Articles

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation.

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity-stability trade-off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas-catalyst-support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25 - 500 °C under dry conditions and 200 - 800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation

AbstractSupported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity‐stability trade‐off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas‐catalyst‐support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25‐500 °C under dry conditions and 200‐800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Mesoporous La0.8Sr0.2CoO3/H-COK-12 catalyst synthesized by template method: Highly active for the complete oxidation of CO

Using cheap sodium silicate as a silica source and surfactant P123 as a soft template, an environment-friendly mesoporous material, COK-12, was prepared in a near-neutral environment. COK-12 was modified with n-hexane to obtain an H-COK-12 template with a compact and ordered pore structure. In this study, the modified mesoporous material H-COK-12 was used as the template for the first time, and the mesoporous La0.8Sr0.2CoO3 (LSC) catalyst was prepared by nano-casting method combined with sol–gel method. The results showed that the LSC-650 catalyst synthesized at 650 °C for 2 h possessed a large specific surface area (103.46 m2/g) and the highest surface Co4+/Co3+ and Oads/Olat molar ratio. In addition, the CO conversion with the LSC-T (T = 550, 600, 650, 700 °C) samples indicated that the LSC-650 sample had the best catalytic activity (T50 = 145 °C, T90 = 149 °C) and stability.

SnO2-modified CuMnOx catalysts for humid CO oxidation at low temperature

Low-temperature CO oxidation has been widely applied in environmental pollution control, but challenges remain in CO purification in high-humidity environments. In this study, the CuMnSn8 catalyst exhibited excellent low-temperature CO oxidation performance, achieving complete CO oxidation at temperatures below 55 °C in 85 % relative humidity. A series of characterizations indicated that an appropriate amount of SnO2 doping could promote the formation of more amorphous oxides, increase the oxygen species content, and facilitate the dispersion of Cu and Mn elements. The catalytic active sites for CO oxidation and the influence of SnO2 doping on the CO oxidation mechanism were investigated through in-situ DRIFTS experiments. The results indicated that Sn enhanced the synergistic effect between Cu and Mn, altered the pathway of CO oxidation reaction, generated more easily decomposable bidentate carbonate intermediates. This work provides insight into the design of CO oxidation catalysts with high activity in high humidity.

Catalytic CO Oxidation on the Cu+-Ov-Ce3+ Interface Constructed by an Electrospinning Method for Enhanced CO Adsorption at Low Temperature.

It is crucial to eliminate CO emissions using non-noble catalysts. Cu-based catalysts have been widely applied in CO oxidation, but their activity and stability at low temperatures are still challenging. This study reports the preparation and application of an efficient copper-doped ceria electrospun fiber catalyst prepared by a facile electrospinning method. The obtained 10Cu-Ce fiber catalyst achieved complete CO oxidation at a temperature as low as 90 °C. However, a reference 10Cu/Ce catalyst prepared by the impregnation method needed 110 °C to achieve complete CO oxidation under identical reaction conditions. Asymmetric oxygen vacancies (ASOV) at the interface between copper and cerium were constructed, to effectively absorb gas molecules involved in the reaction, leading to the enhanced oxidation of CO. The exceptional ability of the 10Cu-Ce catalyst to adsorb CO is attributed to its unique structure and surface interaction phase Cu+-Ov-Ce3+, as demonstrated by a series of characterizations and DFT calculations. This novel approach of using electrospinning offers a promising technique for developing low-temperature and non-noble metal-based catalysts.

PdCu Alloy Catalyst for Inhibition‐free, Low‐temperature CO Oxidation

AbstractDesigning robust catalysts for low‐temperature oxidation is pertinent to the development of advanced combustion engines to meet increasingly stringent emissions limitations. Oxidation of CO, hydrocarbon, and NO pollutants over platinum‐group catalysts suffer from strong inhibition due to their competitive adsorption, while coinage metals are generally slow at activating O2. Through computational screening, we discovered a PdCu alloy catalyst that completely oxidizes CO below 150 °C without inhibition by NO, propylene or water. This is attributed primarily to geometric effects and the presence of CO bound to Pd sites within the Cu‐rich surface of the PdCu alloy. We demonstrate that the novel PdCu catalyst can be used in tandem with a PtPd catalyst to achieve sequential, inhibition‐free, complete oxidation of CO in a two‐bed system, while also achieving 50 % NO conversion below 120 °C. Moreover, neither water nor propylene adversely affect the low temperature CO oxidation activity.

Highly Efficient RGO-Supported Pd Catalyst for Low Temperature Hydrocarbon Oxidation

The work presents Pd-containing catalysts for practical application with enhanced low-temperature activity in the complete oxidation of volatile organic compounds (VOCs) using innovative combinations of reduced graphene oxide (RGO) and alumina. The catalysts were characterized by XRD, SEM, TEM, XPS, low-temperature N2-adsorption, and CO chemisorption. The tests on complete catalytic oxidation of different VOC (propane, butane, hexane, dimethyl ether, toluene, propylene) and CO were carried out. The reaction kinetics and the mechanism of the reaction of complete oxidation of toluene are being investigated in detail. The results show that the new catalyst design makes it able to completely oxidize the studied VOCs and CO at low temperatures (100–350 °C) with long-term stability. Using a variety of instrumental methods, it was established that for high activity and long-term stability, the optimal ratio Pd/PdO should be close to 1:1. The most probable mechanism of complete toluene oxidation is the mechanism of Langmuir–Hinshelwood. The high activity and the weak effect of water on the catalyst performance leads to further perspectives for the application of the currently developed approach for the preparation of large-scale monolithic catalytic systems for air pollution control.

Promotion of oxygen vacancies and metal-support interaction over 3DOM Au/CeO2 catalyst for CO oxidation

CO oxidation is the primary approach for eliminating CO from incomplete combustion, and the catalytic performance is dependent on the structure of catalysts. Herein, to explore the structure promotion in the CO oxidation reaction, polymethyl methacrylate was synthesized as the hard template to fabricate the three-dimensional ordered microporous (3DOM) Au/CeO2 and compared the catalytic performance with the Au/CeO2 rod catalyst. The 3DOM Au/CeO2 catalyst could realize complete CO oxidation at 90 °C while 110 °C for Au/CeO2 rod catalyst. The 3DOM Au/CeO2 catalyst also showed outstanding stability for 60 h reaction. The achieved high performance could be attributed to the pore structures and the better metal-support interaction that facilitates abundant oxygen vacancies. Additionally, the Au distribution and oxygen vacancies promoted by the macropores structures were discovered using a series of characterizations. This work highlights the promotion of oxygen vacancies and metal-support interaction by 3DOM structure in CO oxidation reaction.

Tailored synthesized Pt/ZSM-5 catalysts with excellent water vapor stability for low temperature oxidation of CO and C3H6

Pt supported on ZSM-5 catalysts are important for the catalytic oxidation of CO and volatile organic compounds (VOCs) due to their extraordinary performance at low temperatures and economic purposes. However, achieving complete oxidation at low temperatures and stability under water vapor remains challenging. Herein, we report the synthesis of several loading of Pt on a ZSM-5 catalyst via a flame synthesis technique. The Pt/ZSM-5 exhibited good activity towards complete CO and C3H6 oxidation at low temperatures due to the interaction between the Pt and ZSM-5. The combined effect of the PtOx (Pt2++Pt4+) and lattice oxygen from Pt (OPtOx) as the active centers in Pt/ZSM-5 favors the complete oxidation with high reaction rates, TOFs, and low activation energies (Ea), which is well consistent with the increasing concentration of the (Pt2++Pt4+)/Pt0. Pt/ZSM-5 presents a long-time tolerance to water vapor deactivation even at temperatures below 80 °C. The distributed Pt favor the reaction occurring through the Langmuir-Hinshelwood (L-H) route. The excellent catalytic results indicate an attractive approach for designing supported Pt on ZSM-5 catalysts for automobiles and industry exhausts.

Zn Modification of Pd/TiO2/Ti Catalyst for CO Oxidation.

The main goal of this study was to modify the activity of Pd/TiO2/Ti catalyst in the reaction of CO oxidation by the addition of Zn. Plasma electrolytic oxidation (PEO) of Ti wire was conducted to produce a uniform porous layer of TiO2. A mixture of Pd and Zn was then introduced by means of adsorption. After reduction treatment, the activity of the samples was examined by oxidation of 5% CO in a temperature range from 80-350 °C. Model catalysts with sufficient amounts of the metals for physico-chemical investigation were prepared to further investigate the reaction between Pd and Zn during CO oxidation. The structures and compositions of the samples were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), inductively coupled plasma mass spectrometry (ICP-MS), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). Modification of Pd/TiO2/Ti catalyst by Zn with a Pd:Zn atomic ratio of 2:1 decreased the temperature of complete CO oxidation from 220 °C for Pd/TiO2/Ti to 180 °C for Pd-Zn/TiO2/Ti. The temperature of 50% CO conversion on Pd-Zn(2:1)/TiO2/Ti was around 55 °C lower than in the reaction on monometallic Pd catalyst. The addition of Zn to the Pd catalyst lowered the binding energy of CO on the surface and improved the dissociative adsorption of oxygen, facilitating the oxidation of CO. FTIR showed that the bridging form of adsorbed CO is preferred on bimetallic systems. Analysis of the surface compositions of the samples (SEM-EDS, TOF-SIMS) showed higher amounts of oxygen on the bimetallic systems.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

A review of catalytic oxidation of carbon monoxide over different catalysts with an emphasis on hopcalite catalysts

Hopcalite catalysts are reviewed showing highly active catalysts for low-temperature, low-cost and complete oxidation of CO.

Metal-oxide interactions modulating the activity of active oxygen species on atomically dispersed silver catalysts.

The activity of active oxygen species on supported Ag atoms can be effectively modulated by metal-support interactions using different oxide supports. The strong interaction between Ag and Al2O3 with more electrons transferred from Ag to Al2O3 leads to the formation of more Ag-O2- (superoxide) species, responsible for the selective oxidation of ethylene to ethylene oxide. The relatively weak interaction between Ag and SiO2 induces the generation of Ag-O (atomic oxygen) and Ag-O22- (peroxide) species, which are more active for complete oxidation of CO and ethylene to CO2. This work is of significance for deep understanding of active surface species in atomically dispersed metal catalysts.

Exploring Synthesis Approaches of Co-based Catalysts for the Efficient Oxidation of CH4 and CO

AbstractCo-based catalysts were synthesized and studied as novel oxidation catalysts, exploring and optimizing the effect of synthesis method on the redox behavior, the oxygen storage ability and thus the catalytic performance of the derived Co3O4 materials in the complete CH4 and/or CO oxidation reactions. Thus, a series of Co-based catalysts were synthesized applying either the precipitation and/or the hydrothermal method, using different precipitating agents (Na2CO3, NH3, urea or NaOH), Co precursor salt (nitrate or acetate) and finally varying the Co/Na ratio. In addition, the reaction time (6 or 24 h aging) was also investigated for the hydrothermally prepared Co3O4. The best catalysts for the CH4 oxidation are the precipitated Co3O4, using cobalt acetate as precursor salt and NaOH as precipitating agent, presenting the highest surface areas and the lowest Co3O4 particle sizes. On the other side, hydrothermally prepared cobalt oxides reveal higher performance for CO oxidation, with Co3O4 prepared with cobalt acetate, NaOH and low aging time shown as the optimum materials. The best catalysts were further promoted with incorporation of Pd (0.5wt.%) and explored for both reactions. The addition of Pd enhanced the activity of Co3O4 for CH4 oxidation, while Pd did not improve any further the catalyst performance for CO oxidation, presenting thus the same activity with pure cobalt oxides.

Robust Joule-heating ceramic reactors for catalytic CO oxidation

Joule-heating reactors have the higher energy efficiency and product selectivity compared with the reactors based on radiative heating. Current Joule-heating reactors are constructed with electrically-conductive metals or carbon materials, and therefore suffer from stability issue due to the presence of corrosive or oxidizing gases during high-temperature reactions. In this study, chemically-stable and electrically-conductive (La0.80Sr0.20)0.95FeO3 (LSF)/Gd0.1Ce0.9O2 (GDC) ceramics have been used to construct Joule-heating reactors for the first time. Taking the advantage of the resistance decrease of the ceramic reactors with temperature increase, the ceramic reactors heated under current control mode achieved the automatic adjustment of heating to stabilize reactor temperatures. In addition, the electrical resistance of LSF/GDC reactors can be tuned by the content of the high-conductive LSF in composite ceramics and ceramic density via sintering temperature, which offers flexibility to control reactor temperatures. The ceramic reactors with dendritic channels (less than 100 urn in diameter) showed the catalytic activity for CO oxidation, which was further improved by coating efficient MnO2 nanocatalyst on reactor channel wall. The Joule-heating ceramic reactors achieved complete CO oxidation at a low temperature of 165 °C. Therefore, robust ceramic reactors have successfully demonstrated effective Joule heating for CO oxidation, which are potentially applied in other high-temperature catalytic reactions.

Complete oxidation of CO and propene as model component of diesel exhaust and VOC using manganese oxide supported on octahedral (AlO63−)-Ce3+

The complete oxidation of CO and propene as a model components of diesel engine exhaust and VOC have been investigated on a series of Ce doped MnOx/Al2O3 catalysts. The optimized MnOx/Al2O3 doped with 0.05 mol Ce showed higher CO and propene oxidation activity at 200 °C and 215 °C, respectively. The physicochemical properties of catalysts were analyzed by using XRD, RAMAN, NMR, H2-TPR, HRTEM and XPS techniques. The formation of Mn3O4 and Mn4+ species were observed on the catalyst surface. 27Al solid-state NMR showed the formation of octahedral [AlO63−]-Ce3+ species. These species were responsible for the donation of oxygen required for CO and propene oxidation. The adsorbed oxygen and oxygen vacancies were formed on the catalyst surface due to the synergistic interaction between Mn, Ce, and Al. The HRTEM results showed formation of well dispersed Mn over Ce-O-Al, and facilitated the proton abstraction required to activate the hydrocarbon. The mechanistic and kinetic aspects of CO and propene oxidation on catalyst surfaces have been reported in detail.

A low cost bimetallic AuCu3 tetramer on Ti2CO2 MXene as an efficient catalyst for CO oxidation: a theoretical prediction.

Abatement of CO, due to its poisonous nature, is an extensively researched topic. Oxidation to CO2 is one of the strategies deployed and finds application in automobiles and fuel cells. Gold nanoparticles on an oxide support is a pioneering catalyst in this field, but need improvement in cost, stability, and O2 activation. Doping with Cu can open up avenues for improvement in these attributes. In the present investigation, we have explored the possibility of using bimetallic AunCum (n + m = 4) clusters supported on Ti2CO2 MXene. We find that AuCu3 is the most stable cluster on the support. The complete CO oxidation cycle on this supported cluster proceeds through a mix of Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Our calculations predict that the first cycle is expected to proceed only via the LH mechanism due to kinetic and thermodynamic limitations ascribed to ER and Mars van Krevelen (MvK) mechanisms, respectively. The second cycle, however, prefers ER over the LH mechanism. Overall, with the highest barrier of 0.56 eV, this low cost novel catalyst performs better in terms of stability and/or activity in comparison with many of the catalysts reported in the literature.

CuO Quantum Dots Supported by SrTiO3 Perovskite Using the Flame Spray Pyrolysis Method: Enhanced Activity and Excellent Thermal Resistance for Catalytic Combustion of CO and CH4.

As a non-noble-metal catalyst, CuO has great potential in the catalytic combustion of CO and CH4. In this work, the influence of loading active copper components onto perovskites and essential operating parameters in flame aerosol synthesis has been experimentally and theoretically investigated to optimize the catalytic efficiency for the complete oxidation of lean CO and CH4. Herein, the CuO-SrTiO3 nanocatalysts are one-step-synthesized by flame spray pyrolysis with varied copper loadings and precursor feeding rates. The sample under the precursor flow rate of 3 mL/min and the CuO loading of 15 mol % demonstrates optimal catalytic performance. It is primarily attributed to the excellent low-temperature reducibility and improved activity of copper species originated by CuO quantum dots and metal-support interaction. Besides, SrTiO3 perovskite as a support can effectively inhibit the sintering of CuO quantum dots at high temperatures, which is responsible for the excellent sintering and water deactivation resistances.

Complete CO Oxidation by O2 and H2O over Pt–CeO2−δ/MgO Following Langmuir–Hinshelwood and Mars–van Krevelen Mechanisms, Respectively

Complete CO Oxidation by O₂ and H₂O over Pt–CeO_2−δ/MgO Following Langmuir–Hinshelwood and Mars–van Krevelen Mechanisms, Respectively

HC-SCR system combining Ag/Al2O3 and Pd/Al2O3 catalysts with resistance to hydrothermal aging for simultaneous removal of NO, HC, and CO

A combined Ag/Al2O3 and Pd/Al2O3 catalyst was investigated for the selective catalytic reduction (SCR) of NOx by H2-assisted C3H6 in the presence of excessive O2. The coexistent H2 significantly lowered the active temperature window of the de-NOx reaction because of the enhanced partial oxidation of C3H6 and NO oxidation to NO2. A low Ag loading of 1 wt% exhibited better de-NOx performance than that attained using 2 wt% Ag. Although Ag/Al2O3 exhibited a high resistance to hydrothermal aging, a high reaction temperature (>500 °C) was required to oxidize CO and C3H6 completely. In contrast to Ag/Al2O3, Pd/Al2O3 suppressed C3H6 and CO slip at relatively low temperatures, and a complete oxidation of C3H6 and CO was achieved at 195–275 °C and 240–275 °C, respectively, under varying SCR conditions and Pd contents (0.5–1.5 wt%); however, 30% de-NOx performance in a narrow temperature window of 210–240 °C was attained. The best configuration was found to be a sequential arrangement of 1Ag/Al2O3 followed by 1Pd/Al2O3, which enabled the reduction of NOx, C3H6, CO, and H2 over wide reaction temperatures, unlike the stand-alone configuration. In this configuration, the reacted NOx was reduced to N2 with negligible formation of by-products, even after hydrothermal aging.