Catalytic Combustion Of CO Research Articles

Flame made low Pt loading catalysts supported on different metal oxides for catalytic combustion of CO and CH4

Catalytic combustion is an effective approach to remove air pollutants from various emission sources. For this purpose, supported noble metal catalysts are preferred in commercial applications due to their outstanding catalytic activity for eliminating CO, hydrocarbon compounds and NOx. In this paper, we employ the flame spray pyrolysis method to prepare a series of Pt-based catalysts with four different supports (TiO2, ZrO2, MgO and ZnO) and variable low Pt loadings for catalytic combustion of CO and CH4. The performance of 0.5 Pt/TiO2 is the best in all samples, in which the T90 temperatures are 107 and 500 °C for 90% conversion of CO and CH4, respectively. To examine its thermal stability, a time-on-stream test at 700 °C for 420 min is carried out, resulting in a decrease of about 5% in the final conversion of CH4. The X-ray diffraction results show that TiO2 support is a mixed phase with a major amount of anatase and a small amount of rutile other than a pure phase of ZrO2, MgO and ZnO. Furthermore, X-ray photoelectron spectroscopy analysis and high-angle annular dark-field scanning transmission electron microscopy observation show that when the Pt loading is low, the Pt species exist as highly dispersed single atoms on the surface of the TiO2 support. As the Pt loading gradually increases, the state of the Pt species transitions from single atoms to Pt clusters, resulting in a decrease in dispersion. Ultimately, the Pt can successfully accumulate on the surface of the TiO2 nanoparticles, providing abundant active sites for efficient catalytic combustion reactions.

Self-sustained catalytic combustion of CO enhanced by micro fluidized bed: stability operation, fluidization state and CFD simulation

Self-sustained catalytic combustion of CO enhanced by micro fluidized bed: stability operation, fluidization state and CFD simulation

Effects of Cu2O morphology on the performance of CO self-sustained catalytic combustion

Self-sustained catalytic combustion is a sustainable approach to deal with exhaust gas with high concentration CO, and revealing its reaction process is necessary and challenging. Herein, cube (Cu2O-C), octahedron (Cu2O-O) and dodecahedron (Cu2O-D) exposing different crystal planes were used to explore the catalytic combustion mechanism. The catalytic combustion can be self-sustained on the Cu2O surface and the activities decrease in the order of Cu2O-O > Cu2O-D > Cu2O-C, contributing to the different exposing planes with (1 1 1), (1 1 0) and (1 0 0), respectively. In-situ DRIFTS results prove that the catalytic combustion of CO to CO2 on Cu2O is prone to follow the MvK mechanism. Comparing with Cu2O-D and Cu2O-C, the relatively open surface of Cu2O-O plane composed of unsaturated copper and oxygen atoms facilitates the CO adsorption on Cu (I) and the mobility of lattice oxygen, leading to the highest low temperature reducibility and catalytic activity.

Defect Engineering on CuMn2O4 Spinel Surface: A New Path to High-Performance Oxidation Catalysts.

Catalytic combustion is an efficient method to eliminate CO and volatile organic compound (VOC) pollutants. CuMn2O4 spinel is a high-performance non-noble metal oxide catalyst for catalytic combustion and has the potential to replace noble metal catalysts. In order to further improve the catalytic activity of CuMn2O4 spinel, we propose a simple and low-cost approach to introduce numerous oxygen and metal vacancies simultaneously in situ on the CuMn2O4 spinel surface for the catalytic combustion of CO and VOCs. Alkali treatment was used to generate oxygen vacancies (VO), copper vacancies (VCu), and novel active sites (VO combines with Mn2O3 at the interface between Mn2O3(222) and CuMn2O4(311)) on the CuMn2O4 spinel surface. In the catalytic combustion of CO and VOCs, the vacancies and new active sites showed high activity and stability. The oxidation rate of CO increased by 4.13 times at 160 °C, and that of toluene increased by 11.63 times at 250 °C. Oxygen is easier to adsorb and dissociate on VO and novel sites, and the dissociated oxygen also more easily participates in the oxidation reaction. Furthermore, the lattice oxygen at VCu more readily participates in the oxidation reaction. This strategy is beneficial for the development of defect engineering on spinel surfaces and provides a new idea for improving the catalytic combustion activity of CuMn2O4 spinel.

Enhancing catalytic performance of Ag-CeO2 catalysts for catalytic CO combustion: Ag-CeO2 interface interaction and Na-promoting action

Ag-CeO2 catalysts were prepared via urea- and activated carbon- assisted pyrolysis to study an improvement strategy for their catalytic performance in catalytic CO combustion. Different synthetic methods induced the change of Ag-CeO2 interface interaction by tuning the surface chemical state of Ag nanoparticles and CeO2 nanoparticles. However, it was completely different to arouse the change degree in the structure and performance of these Ag-CeO2 catalysts. Fabrication of Ag-CeO2 catalysts using a urea pyrolysis induced to create an Ag-CeO2 interface with more metallic Ag species, which improved the reductivity of CeO2 surface and enhanced the Ag-CeO2 catalyst performance. Fabrication of Ag-CeO2 catalysts using an activated carbon pyrolysis method induced to form an Ag-CeO2 interface with more positively charged Ag+ ions and required higher temperature of CO conversion. For the Ag-CeO2 catalysts with more positively charged Ag+ species, the participation of sodium salts could alleviate Ag nanoparticle oxidation and promoted the transformation of Ag-CeO2 interface with more positively charged Ag+ ions into Ag-CeO2 interface with more metallic Ag species, which caused the formation of more Ce3+ cations and the production of more reducible surface oxygen and enhanced the catalyst performance in catalytic CO combustion.

Self-Sustained Catalytic Combustion of Co Enhanced by Micro Fluidized Bed: Stability Operation, Fluidization State and Cfd Simulation

Self-Sustained Catalytic Combustion of Co Enhanced by Micro Fluidized Bed: Stability Operation, Fluidization State and Cfd Simulation

Investigation on the catalytic combustion of CO over LaMn1‐xCuxO3 promoted by acid treatment

AbstractThere are large amounts of CO pollutants in the off‐gas of the iron and steel industry, which cause serious harm to the environment and human health. To control the emission of CO more effectively, in this paper, LaMn1‐xCuxO3 (x = 0, 0.25) perovskite catalysts were prepared and then modified by dilute nitric acid. And the physicochemical properties and the catalytic activity of perovskite were investigated and analyzed. The activity results indicate that the Cu2+ substitution and acid treatment could obviously promote the catalytic activity of catalysts for CO oxidation. Among the prepared samples, LaMn0.75Cu0.25O3‐H exhibits the highest activity with 90% CO conversion at 176.5°C, and the self‐sustained combustion of CO is successfully achieved. And the long‐time stability test shows that LaMn0.75Cu0.25O3‐H can keep 100% CO conversion, and the activity remains almost unchanged. Combined with the x‐ray photoelectron spectroscopy (XPS) and H2 temperature‐programmed reduction (H2‐TPR) results, the increased activity of LaMn0.75Cu0.25O3‐H catalyst is mainly ascribed to the high concentration of Mn4+ and abundant oxygen vacancies. On the other hand, the morphology of perovskite catalysts was remolded by acid etching, and the formation of the porous structure significantly increases the specific surface area. The above results show that the substitution of Cu and acid treatment for perovskite catalysts is a feasible strategy to improve CO catalytic combustion activity.

Deep Insight into the Mechanism of Catalytic Combustion of CO and CH4 over SrTi1-xBxO3 (B = Co, Fe, Mn, Ni, and Cu) Perovskite via Flame Spray Pyrolysis.

Perovskites have been recognized as affordable substitutes for noble-metal catalysts for their tunable catalytic activity and thermal stability. Nevertheless, the highly demanding synthesis procedure still hinders the application of perovskites in catalytic combustion. In this work, a series of nanostructured SiTiO3 perovskites with B-site partial substitution by Co, Fe, Mn, Ni, and Cu are synthesized via flame spray pyrolysis in one step. The comprehensive characterizations on textural properties of nanostructured perovskites reveal that the flame-made perovskite nanoparticles all exhibit high crystal purity and large specific surface area (∼40 m2/g). Furthermore, the highest catalytic activity is achieved by SrTi0.5Co0.5O3 due to the formation of favorable oxygen vacancies, outstanding reducibility, and oxygen desorption capability. Additionally, the presence of 10 vol % water vapor during long-term testing indicates remarkable durability and water resistance. Finally, the CO oxidation and CH4 dehydrogenation on SrTiO3 incorporating Co atoms are more thermodynamically and kinetically favorable than those on other doped surfaces.

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.

Mechanisms and energetics of CO oxidation on MnO2-supported Pt13 clusters

The interface formed by metal clusters supported on (reducible) transition metal oxides (TMOs) is usually responsible for the excellent activity of the redox reaction in the heterogeneously catalytic field. In this work, the catalytic combustion of CO was selected as a typical probe reaction to theoretically reveal the features of Pt13/β-MnO2 (1 1 0) catalyst, which possesses four active sites i.e., interface, β-MnO2 (1 1 0) facet, metallicity (Pt0) and partial oxidized Pt (Ptx+). All active sites were carefully investigated by the characteristics of CO oxidation. For Pt0 and Ptx+ sites, the adsorption energies of CO are larger than those of O2, which might block O2 active sites and cause CO poison. Meanwhile, CO oxidation by the dissociated O atom has the relatively high reaction energy barrier. Thus, Pt0 and Ptx+ are not good active sites for CO oxidation. For β-MnO2 (1 1 0) facet, O2 dissociation is not easy with a high barrier for vacancies healing. In contrast, the most favorable mechanism of CO oxidation is the catalytic cycle at the interface, with low reaction energy barriers in the entire pathway. We hope this comprehensive work can provide a meaningful reference towards the design of heterogeneous catalysts.

Study on activity, stability limit and reaction mechanism of CO self-sustained combustion over the LaMnO3, La0.9Ce0.1MnO3 and La0.9Sr0.1MnO3 perovskite catalysts using sugar agent

The LaMnO3, La0.9Ce0.1MnO3 and La0.9Sr0.1MnO3 catalysts are synthesized using sugar agent, and the CO self-sustained combustion is investigated, where the catalytic performance is decided by temperature with CO conversions of 10% (T10), 50% (T50), and 90% (T90). The results show that self-sustaining combustion is successfully realized on the catalyst, and the order of activity decrease is as follows: La0.9Ce0.1MnO3 (with sugar) > La0.9Sr0.1MnO3 (with sugar) > LaMnO3 (with sugar) > LaMnO3 (without sugar) > La0.9Sr0.1MnO3 (without sugar) > La0.9Ce0.1MnO3 (without sugar). Combined with the results of XPS, H2-TPR, O2-TPD and CO-TPD techniques, the excellent activity of La0.9Ce0.1MnO3 (with sugar) can be attributed to the high content of Mn4+ ions and reactive oxygen vacancies enriched on the catalyst surface, sound low-temperature reduction, and uniform dispersion. Besides, in situ IR spectroscopy results indicate that the catalytic combustion of CO over manganese-based perovskite catalysts follows the L-H mechanism: the chemisorption of CO and O2 takes place to produce monodentate carbonates and bicarbonate species, which then decompose to yield CO2 release. The high-temperature stability test provides evidence that the La0.9Ce0.1MnO3 (with sugar) gives 100% CO conversion and that the activities remain almost unchanged after reaction for 12 h, where the temperature of catalyst bed reaches about 717 °C. The results obtained are helpful to accept this technology on efficient and clean energy utilization in iron and steel industry.

Catalytic combustion of CO over Cu-doped iron oxides: CO2 effects on activity

This study reports the catalytic combustion application of FeCuOx thin films synthesized through a doping strategy with different Fe/Cu molar ratios via one-step synthesis route. Structure analysis of the as-prepared thin film reveals the formation of single-phase delafossite structure. A smooth hollows film surface with agglomerated grains was observed. With the introduction of Cu content, Cu+ was successfully embedded in Fe2O3 lattice to form substituted structure, whereas the ratio of OLatt/OAds tended to increase. The perceived behavior was ascribed to the progressive incorporation of Cu, which brought structural changes favoring the formation of anionic vacancies and the mobility of oxygen. The catalytic activity was investigated through the complete catalytic combustion of CO with a high GHSV of 184,500 mL·g−1·h−1, which is closer to actual engineering for the commercial application of the catalytic combustion. The addition of higher quantity of Cu transferred the conversion curvature toward lower temperatures, due to active Cu, Fe and surface oxygen species. Moreover, the effects of CO2 interaction on the reaction mixture was analyzed in order to assess the performance of thin film catalysts under realistic conditions of reaction. Although the principal inhibitor effect was associated with the CO2, the progressive introduction of CO2 in the reaction, gave rise to a decrease of the CO conversion. Furthermore, theoretical calculations based on DFT method of CO with CO2 oxidation over CuFeO2 delafossite film surface catalyst demonstrated that the existence of CO2 acted as an inhibitor in the CO adsorption process which led the reaction to higher temperature.

Gas sensing technologies in combustion: A comprehensive review

Irrespective of the change in kind of energy to renewables there are many processes in which combustion of conventional fuels and biofuel are necessary. For cement and glass production, paper fabrication and air traffic it is absolutely essential to control the combustion processes by intelligent sensors in order to maximize the efficiency and to minimize the emission of harmful substances such as NOx and CO. Mainly oxygen sensors based on solid electrolytes and calorimetric sensors using the heat formation by catalytic combustion of CO and hydrocarbons with two resistance temperature detectors (RTD) are utilized. Recently, tunable diode laser spectroscopy (TDLS) became attractive in chemical plants. Several analytical companies are offering in-situ or extractive laser analyzers for combustion gases.

Facile synthesis of a CuMnOx catalyst based on a mechanochemical redox process for efficient and stable CO oxidation

Low-temperature catalytic combustion of CO is a desirable route for CO removal. We reported the sythesis of highly active CuMnOx catalyst by a mechanochemical redox process.

Self-sustained catalytic combustion of carbon monoxide ignited by dielectric barrier discharge

This paper presents the results of a study of self-sustained catalytic combustion of CO ignited by dielectric barrier discharge (DBD) using Ce0.5Zr0.5Oy/TiO2 (CeZr/Ti), CuZr0.25Oy/TiO2 (CuZr/Ti), and CuCe0.75Zr0.25Oy/TiO2 (CuCeZr/Ti) catalysts. DBD excites and dissociates some of the reactant molecules in the gas phase. These are more easily adsorbed on the catalyst surface than are ground-state species, therefore induction begins at a lower background temperature than in thermal catalysis. CO is adsorbed on copper sites, therefore CeZr/Ti is inactive in CO ignition, but CuZr/Ti and CuCeZr/Ti achieve DBD ignition at 34 and 44s, respectively, at a specific energy density (SED) of 1500J/L. CO catalytic ignition by DBD involves two steps. The induction process is dominated by plasma catalysis. At the same SEDs, induction with CuCeZr/Ti begins earlier than those with CuZr/Ti, in good agreement with the reducibilities and oxygen-transfer properties of these catalysts. The ignition process is governed by thermal catalysis because the enhancement of external diffusion induced by increasing the temperature improves the reaction rate. CuZr/Ti provided more CO adsorption sites than did CuCeZr/Ti, contributing to shortening of the ignition delay.

Nanocrystalline Ce1−xRuxO2 – Microstructure, stability and activity in CO and soot oxidation

Nanocrystalline (4–5nm) Ce1−xRuxO2 mixed oxides (x=0.03–0.16) were synthesized using water in oil microemulsion method. Morphology, microstructure and a phase composition of the samples subjected to heat treatment in oxidizing and reducing atmosphere were investigated by TEM, SEM-EDS-EBSD, XRD and XPS. Oxide with x=0.11 was structurally stable in oxidizing atmosphere up to 550°C but above this temperature it decomposed into Ru deficient, nanosized Ce1−xRuxO2 and large (few μm) RuO2 crystals. No phase separation was observed for Ce0.97Ru0.03O2 even after heating at 800°C. Doping with Ru decreases the size of ceria particles and strongly hinders their sintering at high temperatures. In hydrogen atmosphere a segregation of small (∼1nm) Ru crystallites occurred at the surface of the Ce0.89Ru0.11O2 mixed oxide. Only small increase of the mean crystallite size of Ru (to 2nm) occurred after reduction at 1000°C. The unique resistance of Ru to sintering is assigned to a special epitaxial orientation Ru (002)∥CeO2 (111), which persisted up to the highest temperature of reduction, due to very strong surface bonding. Contrary to a situation in oxidizing atmosphere, doping with Ru had no significant effect on the sintering of ceria in hydrogen. Partial substitution of Ru for Ce strongly enhances the reducibility of ceria at low temperatures and its activity in catalytic combustion of CO and soot.

Catalytic performance of LaCo0.5M0.5O3 (M = Mn, Cr, Fe, Ni, Cu) perovskite-type oxides and LaCo0.5Mn0.5O3 supported on cordierite for CO oxidation

Catalytic combustion of CO over perovskite-type oxides LaCo0.5M0.5O3 (M=Mn, Cr, Fe, Ni, Cu) and LaCo0.5Mn0.5O3 supported on cordierite were investigated. The catalysts were synthesized by impregnation method with citrate and characterized by XRD, SEM and TPR. The LaCo0.5Mn0.5O3 catalyst showed much higher activity in CO oxidation compared with LaCo0.5M0.5O3 (M=Cr, Fe, Ni, Cu) due to different kinds of valence state and lattice oxygen content. When LaCo0.5Mn0.5O3 was supported on cordierite, the activity was improved significantly. However, calcining temperature and the presence of water vapor affected the catalytic activity due to sintering and competition of H2O with CO for adsorption, respectively.

Deactivation Behavior of Cu<sub>X</sub>Ce<sub>1-X</sub>O<sub>2-X</sub>/SBA-15/Cordierite Monolithic Catalysts for Catalytic Combustion of CO

A series of CuxCe1-xO2-x/SBA-15/cordierite (x = 0-1) catalysts were prepared. The activity of the catalysts for CO combustion was evaluated. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). Deactivation behavior of the catalysts for the catalytic combustion of CO was investigated. The results show that all of the catalysts retained the SBA-15 mesoporous structure. It is proposed that deactivation of the catalysts is associated with the increase of the Cu+ and the decrease of the Cu2+ in the catalysts.

CeO 2-Y 2O 3 Washcoat and Supported Pd Catalysts for the Combustion of Volatile Organic Compounds (VOCs)

A novel CeO 2-Y 2O 3 (denoted as CeY) washcoat adhered to the cordierite honeycomb was prepared. The preparation technique, using nano-sized CeO 2 and yttrium citrate as precursors, was friendly to environment because no deleterious products were formed during the operation. The CeY washcoat support and Pd/CeY catalysts were characterized using scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF) spectrometer, and Raman spectroscopy. The results showed that the washcoat had sufficient adhesion and high adsorption efficiency for active species and was suitable for supporting Pd catalysts. For the catalysts, most of Y 2O 3 entered into the channel of the cordierite honeycomb, whereas CeO 2 and Pd enriched on the surface. Furthermore, model reactions for the catalytic combustion of CO, toluene, and ethyl acetate were carried out to evaluate the performance of the Pd/CeY catalyst. It exhibited fairly good catalytic activity and thermal stability. For those catalysts calcined at 500 °C, the T 99 (the lowest reaction temperature when the conversion is 99%) of CO, toluene, and ethyl acetate was 150, 220, and 310 °C, respectively, whereas for those catalysts calcined at 1050 °C, the T 99 of CO, toluene, and ethyl acetate was 180, 250, and 330 °C, respectively. Catalysts calcined at higher temperature, the crystallite size of active species (PdO) increases, which possibly results in a decline in the catalytic activity.

Size and composition dependence in CO oxidation reaction on small free gold, silver, and binary silver–gold cluster anions

Gas phase kinetics experiments with mass-selected gold, silver, and binary silver–gold cluster ions in a radio frequency (rf)-ion trap reactor are presented. For the catalytic CO combustion reaction, the adsorption of molecular oxygen onto the free clusters is identified as the first reaction step. A comparison of the measured O 2 adsorption reaction rate constants for the investigated Ag n Au m − ( n + m = 1, 2, 3) clusters reveals a pronounced size and composition dependence. Favorable activation of the oxygen molecular bond is only expected in the case of Au 2 −. In the reaction of the gold dimer with O 2 and CO, a coadsorption complex is identified at cryogenic temperatures as decisive reaction intermediate in the observed CO oxidation reaction. Through detailed reaction kinetics measurements in combination with first-principles calculations, a comprehensive understanding of the molecular details of the catalytic reaction cycle emerges. The obtained data also permit the determination of the CO 2 formation rate and the catalytic turn-over-frequency in the rf-ion trap reactor. In contrast to gold, odd size silver cluster anions are found to adsorb two oxygen molecules. These Ag n O 4 − complexes are proposed to be key intermediates in oxidation reactions with silver clusters involved, and first experimental indications for catalytic activity of selected cluster sizes are presented.