Complete Oxidation Of CO Research Articles

Ternary composite oxide catalysts CuO/Co3O4–CeO2 with wide temperature-window for the preferential oxidation of CO in H2-rich stream

A series of ternary composite oxide catalysts CuO/Co3O4–CeO2 with variable Ce/(Co+Ce) atomic ratios were prepared and employed for the preferential oxidation of CO (CO PROX). Many techniques such as N2-sorption, XRD, H2-TPR, O2-TPO, CO-TPD, O2-TPD, Cu K-edge XAFS (including EXAFS and XANES) and in situ DRIFTS were used for catalyst characterization. The catalyst CuO/Co3O4–CeO2 with Ce/(Ce+Co) ratio of 0.1 exhibits the best performance, showing not only the lowest temperature for the complete oxidation of CO (98°C), but also the broadest operating temperature window for full CO conversion (98–173°C). The results of N2-sorption and temperature-programmed characterizations including H2-TPR, O2-TPO, CO-TPD and O2-TPD show that the CuCoCe10 catalyst possesses the highest BET surface area, the best reducibility/oxidizability and the best performance for CO and O2 adsorption. Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cu species including Cu0, Cu+ and Cu2+ species co-exist in the spent catalyst CuCoCe10. Stable Cu+ carbonyl species are identified as the main active reaction intermediates as revealed by in situ DRIFTS. High temperature (>120°C) can lead to the reduction of Cu+ to Cu0, enhancing H2 oxidation; as a result, the selectivity of O2 towards CO2 is decreased. Based upon in situ DRIFTS results, a potential CO PROX mechanism over CuO/Co3O4–CeO2 catalysts is proposed.

Nanosized Au supported on three-dimensionally ordered mesoporous β-MnO2: Highly active catalysts for the low-temperature oxidation of carbon monoxide, benzene, and toluene

Three-dimensionally (3D) ordered mesoporous β-MnO2-supported Au nanocatalysts (Au/β-MnO2(urea), Au/β-MnO2(NaOH), and Au/β-MnO2(Na2CO3)) with an Au loading of 5wt.% were prepared by the deposition–precipitation method using urea, NaOH and Na2CO3 as precipitating agent, respectively. The physicochemical properties of the materials were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the complete oxidation of CO, benzene, and toluene. It is shown that the nature of precipitating agent had an important influence on the physicochemical properties of the β-MnO2 support, Au nanoparticles, and Au/β-MnO2 catalysts. Among the three Au/β-MnO2 samples, the Au/β-MnO2(NaOH) showed the highest surface atomic ratios of Mn3+/Mn4+, Oads/Olatt, and Au3+/Au0. The loading of gold could greatly modify the reducibility of Au/β-MnO2 via the strong interaction between the gold and the β-MnO2 support, and the Au/β-MnO2(NaOH) sample possessed the best low-temperature reducibility. Gold loading resulted in a significant enhancement in catalytic activity of β-MnO2. The three Au/β-MnO2 catalysts outperformed the Au-free β-MnO2 catalyst, among which the Au/β-MnO2(NaOH) one showed the best catalytic activity (T50% and T100%=48 and 70°C for CO oxidation, 200 and 250°C for benzene oxidation, and 170 and 220°C for toluene oxidation, respectively). It is concluded that factors, such as the better gold dispersion, higher surface Au3+ and oxygen adspecies concentrations, better low-temperature reducibility, stronger synergistic action between the gold and the support as well as the high-quality 3D ordered mesoporous structure of the support, might be responsible for the excellent catalytic performance of Au/β-MnO2(NaOH).

Oxidation of CO in the presence of SO2 using gold supported on La2O3/TiO2 nanofibers

Commercial catalysts currently available for catalytic incineration of sulfur compounds to SO2 in Claus tail gas do not engender complete oxidation of CO to CO2. This limitation thus prevents implementation of catalytic incineration in a growing number of jurisdictions which require complete CO oxidation. The aim of this study is therefore to develop a catalyst for CO oxidation which is effective in the presence of SO2 and water over a temperature range of 573–873K, which is the typical adiabatic temperature range for Claus tail gas incineration. In this research, two Au–La2O3–TiO2 nano-catalysts have been prepared using, in one case, deposition of Au and La2O3 on TiO2 nano-materials and, in a second case, by deposition of Au on a co-precipitated TiO2–La2O3 nano-material. The synthesized catalysts were characterized using electron microscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and infrared spectroscopy. The resulting materials showed very high CO conversion above 323K and remained active over prolonged periods in the presence of SO2 and other sulfur compounds. The very high catalytic activity of the co-precipitated catalyst was attributed to the presence of cationic Au and a low level of sulfate formation on the nano-fiber support.

Effect of periodic lean/rich switch on methane conversion over a Ce–Zr promoted Pd-Rh/Al2O3 catalyst in the exhausts of natural gas vehicles

The behavior of a commercial Ce–Zr promoted Pd-Rh/Al2O3 catalyst for the abatement of methane from the exhausts of natural gas vehicles (NGVs) is studied in presence of large amounts of water under both stationary conditions and by periodically switching from lean to rich feed. Under stationary conditions with both stoichiometric (λ=1.00) and lean (λ=1.02) feed catalyst deactivation is observed after prolonged exposure to the reaction mixture. Periodic rich pulses in a constant lean feed gas result in the stabilization of catalytic performances.A higher methane conversion than those obtained with stoichiometric and lean feed mixtures is observed under rich conditions, during an experiment carried out by performing lean pulses (λ=1.02) in a constant rich feed gas (λ=0.98). The analysis of reactants conversion and products distribution suggests that different chemistries are involved under lean and rich conditions. Only reactions of complete oxidation of H2, CO, CH4 and NO occur under excess of oxygen, whereas under rich conditions NO reduction, CH4 steam reforming and water gas shift also occur.The effect of symmetric oscillation of the exhausts composition around stoichiometry is also addressed by periodically switching from slightly rich to slightly lean composition with different oscillation amplitudes (Δλ=±0.01, ±0.02 and ±0.03). Higher and more stable methane conversion performances are obtained than those observed under constant λ operations. The presence of a more active PdO/Pd0 state is suggested to explain the enhancement of catalytic performances.

Fabrication of Ag–CeO2 core–shell nanospheres with enhanced catalytic performance due to strengthening of the interfacial interactions

Interfacial interactions are often found in human medical devices, hybrid solar cells, and catalysis. However, there is a lack of control of these interactions when tailoring the materials properties for many technological applications. As a case study, we reported on the synthesis of Ag–CeO2 core–shell nanospheres with the aim of strengthening the interfacial interactions to give enhanced catalytic performance. All core–shell nanospheres were synthesized by a surfactant-free method with a subsequent annealing redox reaction. Systematic sample characterizations indicate that metallic Ag cores with a diameter of 50–100 nm were wrapped by assembled nanoparticles of CeO2 with a shell thickness of 30–50 nm to form a nano-scale core–shell structure. The interfacial interactions between the Ag core and CeO2 shell were strengthened by annealing, surprisingly, as followed by generation of oxygen vacancies to provide abundant of absorption sites for oxygen species. As a consequence, the temperature for oxygen spilling was lowered to 79 °C, and the catalytic performance was abnormally enhanced, as indicated by complete CO oxidation at 120 °C with no sign of deactivation, even when the reaction time is beyond 100 h. The reaction products were desorbed quickly from the surfaces of the core–shell nanospheres, which accounts for their superior stability during catalytic reactions.

Selective CO oxidation in a hydrogen-rich stream over Ru/SiO2

We prepared various Ru catalysts supported on silicas with different surface areas by an incipient wetness impregnation method and applied them in selective CO oxidation in a H2-rich stream. For comparison, complete CO oxidation was also examined. The physical properties were probed with N2 physisorption. The Ru dispersion was measured with CO chemisorption and transmission electron microscopy (TEM). The interaction between the catalyst surface and a reactant was examined with O2 chemisorption, temperature-programmed oxidation (TPO), and temperature-programmed reduction (TPR). The BET surface area and total pore volume of the silica decreased with increasing calcination temperature. The average pore diameter of the silica increased with calcination temperature. The existence of micropores was not observed in the silica calcined in air at temperatures of 1103K and above. The amount of CO and O2 chemisorbed on Ru/SiO2 at 300K decreased with decreasing surface area of the silica. The particle size of Ru metal in Ru/SiO2 generally increased with decreasing surface area of the silica. Ru/SiO2 with a larger Ru particle size showed superior catalytic activities for the complete CO oxidation and the selective CO oxidation in a H2-rich stream, compared to Ru/SiO2 with a smaller Ru particle size, which might be due to the resistance to oxidation of Ru metal into RuOx species. The Ru particle size also affects the fraction of active surface oxygen. Selected Ru/SiO2 catalysts can reduce a high inlet CO concentration to less than 10ppm even in the presence of H2O and CO2.

Catalytic activity of Co-åkermanite and Co-pyroxene in oxidation reactions

Two calcium–cobalt silicates were synthesized in which cobalt occupies different structural positions. The crystal phases belong to two main structural silicate types. In the Co-åkermanite structure (Ca2CoSi2O7), cobalt cations take tetrahedral coordination toward oxygen atoms. In the Co-pyroxene structure of CaCoSi2O6, cobalt displays octahedral coordination. Ca2CoSi2O7was prepared by solid-phase synthesis and CaCoSi2O6was prepared by sol–gel method. The synthesis of the phases was confirmed by XRD, FTIR, and EPR data. On the basis of the XPS analysis, it can be concluded that Co2+cations exist in the studied silicates. Thus, it is possible to study the catalytic activity of two silicate phases containing Co2+cations in different coordinations: tetrahedral and octahedral. It was found that cobalt silicates with crystal structures corresponding to pyroxene and åkermanite possess catalytic activity in the reactions of complete oxidation of CO and toluene. Co-pyroxene exhibits higher catalytic activity than Co-åkermanite, but the higher cobalt content on the surface of Co-pyroxene should also be taken into account. Then, it turns out that catalytically active complexes with Со2+ions in tetrahedral coordination are more efficient than those with such ions in octahedral coordination when equal concentrations of cobalt were used on the surface of the catalysts.

The effects of Bi 2O 3 on the CO oxidation over Co 3O 4

The Co 3O 4 and Bi 2O 3–Co 3O 4 were prepared by precipitation and co-precipitation method. The samples were characterized by XRD, BET, H 2-TPR, Raman, XPS and EPR. The low-temperature CO oxidation on the catalysts was also investigated. The results showed the deposition of Bi 2O 3 enhanced the activity and stability of Co 3O 4 for CO oxidation. 20 wt.% Bi 2O 3–Co 3O 4 could completely convert CO as low as −89 °C, and maintain the complete oxidation of CO at −75 °C for 10 h. XRD and Raman results showed Bi 2O 3 could enter the lattice of Co 3O 4, and promote the formation of the lattice distortion and structural defect. H 2-TPR results showed that reduction of Co 3O 4 was promoted and the diffusion of oxygen was accelerated. XPS and EPR results showed the surface richness of Co 3+ and the increase of Co 2+ in 20 wt.% Bi 2O 3–Co 3O 4. The formation of more Co 2+ in 20 wt.% Bi 2O 3–Co 3O 4 could produce structure defects and lead to the formation of more oxygen vacancy, which was suggested to play the critical role in promoting the catalytic activity and stability of 20 wt.% Bi 2O 3–Co 3O 4.

Effect of Co-content on the structure and activity of Co–Al hydrotalcite-like materials as catalyst precursors for CO oxidation

The present investigation was undertaken in an endeavor to study the effect of the cobalt content on the structure and activity of Co–Al hydrotalcite-like materials as catalyst precursors for CO oxidation by varying the Co 2+/Al 3+ atomic ratio, thermal treatment of the samples and the reaction temperature. The samples (Co 2+/Al 3+ = 0.5, 1.5, 3.0) have been synthesized by the co-precipitation method. The unsupported Co 3O 4 has been prepared according to the same procedure as the reference compound in order to reveal the role of Al 3+ ions presence. The physicochemical characterization of the uncalcined, hydrothermally treated, calcined and tested samples has been accomplished appropriately by ICP-AES, N 2 adsorption, Powder X-ray diffraction technique and Diffuse Reflectance Spectroscopy and H 2-TPR measurements. The samples were examined by a number of heating–cooling cycles during the activity tests as a procedure to screen the most active catalyst precursor. It was established that the hydrotalcite-like structure of all uncalcined samples had been completely destroyed during the CO oxidation reaction. A concomitant phase transformation into poorly crystallized spinel-type Co 2+(Co 3+,Al 3+) 2O 4 mixed oxide occurred. This spinel-like mixed oxide phase is better organized in all samples after their calcination at 500 °C. The TPR examinations reveal concomitant presence of high-temperature reduced non-stoichiometric CoAl 2O 4. It was found out that the Co–Al mixed oxide, derived from the sample with the highest cobalt loading (Co 2+/Al 3+ = 3.0) preserves a complete and prolonged CO oxidation ability even after cooling down to ambient temperature. On the contrary, the samples with ratios Co 2+/Al 3+ = 0.5 and 1.5 as well as the Co 3O 4 oxide deactivate more rapidly during the cycles. A hypothetic scheme is proposed for activation/deactivation of the catalysts. It is related to the oxygen ion-radicals O 2 x– stabilization by Al 3+ cation association with the Co 2+/Co 3+ redox couple via anionic vacancy.

Carbon monoxide oxidation at room temperature on Pt/CeO2–ZrO2–Bi2O3 catalysts

A novel Pt/CeO(2)-ZrO(2)-Bi(2)O(3) catalyst was prepared to realize complete CO oxidation at room temperature or below even in the presence of moisture. Using this catalyst, a high CO oxidation activity and a high stability against moisture have been realized simultaneously.

Preparation of Au/Y 2O 3 and Au/NiO catalysts by co-precipitation and their oxidation activities

The objective of this work was to investigate the catalytic activity of gold catalysts supported on two metal oxides, yttrium oxide and nickel oxide, prepared by co-precipitation for CO and methanol oxidation reactions. The TGA and XRD results confirmed that yttrium hydroxide (Y(OH) 3) was formed at calcination temperature below 300 °C. When it was calcined at 400 °C, the Y(OH) 3 was transformed to yttrium oxide hydroxide (YOOH). Finally, when calcination temperature was raised to 600 °C, the YOOH was completely transformed to yttrium oxide (Y 2O 3). Interestingly, the gold loaded on YOOH calcined at 400 °C and gold loaded on Y 2O 3 calcined at 500 °C comparatively showed the highest catalytic activity for complete CO oxidation at a reaction temperature of 300 °C. The 0.12% Au/Y 2O 3 catalyst calcined at 500 °C was employed for both CO and methanol oxidation studies. For complete CO oxidation, the reaction temperatures of Au/Y 2O 3 and Au/NiO catalysts were 325 °C and 250 °C, respectively. The light-off temperatures of Au/Y 2O 3 and Au/NiO catalysts for methanol oxidation were 210 °C and 205 °C, respectively. Conclusively, the Au/Y 2O 3 clearly exhibited the same activity as that of Au/NiO for methanol oxidation while the Au/NiO gave higher activity for CO oxidation.

Reaction of ethanol on oxidized and metallic cobalt surfaces

The reaction of ethanol on metallic and oxidized cobalt surfaces was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) in order to determine the dependence of the reaction pathways on the cobalt oxidation state. The primary reaction for ethoxide species on metallic cobalt surfaces was decarbonylation producing CO, H 2 and carbon. This reaction was facile and occurred below 400 K. In contrast, CoO x surfaces which predominantly contained Co 2+ were selective for the dehydrogenation of ethoxide groups to produce acetaldehyde at 400 K. A fraction of the acetaldehyde molecules produced by this pathway were further oxidized to acetate which decomposed to produce CO 2 at 495 K. More highly oxidized Co surfaces that contained both CO 2+ and Co 3+ were active for the complete oxidation of ethanol producing CO, CO 2, and H 2O as the primary products. The insights that these results provide for understanding the mechanism of the steam reforming of ethanol on cobalt catalysts is discussed.

Enhanced performance of Ru nanoparticles confined in carbon nanotubes for CO preferential oxidation in a H 2-rich stream

5 wt.% Ru nanoparticles confined in the channels or dispersed on the outside surfaces of carbon nanotubes (CNTs) were prepared using ultrasonication-added capillarity action or deposition, affording two kinds of catalysts labeled as 5 wt.% Ru/CNTs-in and 5 wt.% Ru/CNTs-out. Characteristic studies by high-resolution transmission electron microscopy, X-ray powder diffraction and H 2-temperature programmed reduction revealed that the Ru nanoparticles existed in highly dispersion with a mean Ru particle size of 1.8 nm in the samples of 5 wt.% Ru/CNTs-in and 5 wt.% Ru/CNTs-out. The catalysts were evaluated for preferential oxidation of CO in hydrogen (CO-PROX). For a hydrogen-rich feed gas containing 1.0% CO and 1.0% O 2, the 5 wt.% Ru/CNTs-in catalyst showed the best activity with complete CO oxidation at the temperature window of 333–393 K. The CO-PROX performance at 373 K was stable for more than 100 h. However, lower CO conversion and narrower temperature window were obtained over the 5 wt.% Ru/CNTs-out catalyst and 5 wt.% Ru nanoparticles supported on other carriers under identical conditions. It is concluded that the nano-channels of CNTs can selectively increase the density of reactants and the encapsulation of Ru nanoparticles in the channels of CNTs can provide a micro-environment to reinforce the reactivity of catalytic sites.

The effect of the crystalline phase of alumina on the selective CO oxidation in a hydrogen-rich stream over Ru/Al2O3

We prepared Ru catalysts supported on various aluminum oxides with different crystalline phases, viz. α-Al2O3, κ-Al2O3, γ-Al2O3, η-Al2O3, δ-Al2O3 and θ-Al2O3, by the incipient wetness method and applied them to the selective CO oxidation in a hydrogen-rich stream. For comparison, the complete CO oxidation in the absence of H2 was also carried out over the same catalysts. Ru/α-Al2O3 showed the highest CO conversion among the tested catalysts, especially at low temperatures, irrespective of the presence of H2. For all of the catalysts, the catalytic activity for CO oxidation was much suppressed in the absence of H2 compared with that in the presence of H2. Several techniques: N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), CO chemisorption, temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO2 with mass spectroscopy and transmission electron microscopy (TEM) were employed to characterize the catalysts. The least amount of chemisorbed CO and CO2 was obtained at room temperature over Ru/α-Al2O3. The least amount of O2 was chemisorbed during TPO and the oxidized Ru species could be fully reduced in the presence of hydrogen at the lowest temperature over Ru/α-Al2O3 among the Ru/Al2O3 catalysts. Ru/α-Al2O3 can reduce a high inlet concentration of CO to less than 10ppm even in the presence of H2O and CO2 over a wide temperature range.

Production of intermetallic catalysts of deep CO and hydrocarbon oxidation

The possibility of producing (Ni, Co, Mn) Alx intermetallides using the technique of self-propagating high-temperature synthesis and their subsequent processing with the purpose of using them as catalysis in the process of complete oxidation of CO and hydrocarbons is considered. Phase composition, microstructure, and morphology of alloys and catalysts based on them are studied. Dependences of activity and stability on composition are determined. These catalysts are shown to possess high activity and their development is considered to be a promising direction in the catalysis of deep oxidation processes.

Sialon-supported catalysts for deep oxidation of carbon monoxide and hydrocarbons

Catalysts supported on a new class of supports—β-Sialons Si6 − zAlzOzN8 − z (z = 1, 3, 4) modified with transition-metal oxides—were synthesized and tested in the complete and partial oxidation of hydrocarbons and CO. These Sialons were prepared by self-propagating high-temperature synthesis (SHS). Catalytic activity in the test reactions appeared in systems that contain unary, binary, or ternary mixtures of metal oxides of the second half of the 3d row. Cobalt oxide-based catalysts showed the highest activity. Methods were proposed for activating Sialon supports with a considerable enhancement of the activity of a supported catalyst. More precise investigative tools are required for refining new data and understanding the nature and operation mechanism of Sialons. On account of their high thermal stability and wear resistance, Sialon-supported catalysts are proposed for use in deep oxidation processes in abrasive and acid solutions and at elevated temperatures.

Modeling of the catalytic removal of CO and NO in dry combustion gases

Catalytic removal of pollutants in dry combustion gases in a planar stagnation-point flow over a platinum foil is studied using both numerical and analytical tools. The governing equations have been numerically integrated with the Newton technique, and the response curve has been obtained as functions of temperature and the mixture concentrations. Using the appropriate stoichiometry, the additional oxygen needed to reduce the NO and to achieve complete oxidation of CO has been obtained. The asymptotic analysis leads to an algebraic equation for the surface coverage of empty sites as a function of two nondimensional parameters: the mass transfer number, relating the residence time to the chemical time (sort of Damkohler number), and a parameter, which relates the desorption rate to the adsorption rate of carbon monoxide and depends strongly on temperature. Critical conditions of ignition (light-off) and extinction are identified and closed form solutions are obtained for these phenomena. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Rh−Pt Bimetallic Catalysts: Synthesis, Characterization, and Catalysis of Core−Shell, Alloy, and Monometallic Nanoparticles

Rh@Pt core-shell, RhPt (1:1) alloy, and Rh + Pt monometallic nanoparticles (NPs) were prepared using standard polyol reduction chemistry in ethylene glycol (EG) with standard inorganic salts and polyvinylpyrrolidine (PVP(55000)) stabilizers. PVP-free colloids were also prepared but less stable than the PVP-protected NPs. Rh@Pt core-shell particles were prepared from 2.7, 3.3, and 3.9 nm Rh cores with varying shell thicknesses (approximately 1 and approximately 2 ML). The particles were characterized by a combination of TEM, single-particle EDS, EDS line scans, XRD analysis, Debye Function simulations, FT-IR, and micro-Raman CO-probe experiments. The three different architectures were evaluated for preferential oxidation of CO in hydrogen (PROX) using 1.0 wt % Pt loadings in Al(2)O(3) supports. For hydrogen feeds with 0.2% CO and 0.5% O(2) the Rh@Pt NP catalyst has the best activity with complete CO oxidation at 70 degrees C and very high PROX selectivity at 40 degrees C with 50% CO conversion.

Co3O4 + CeO2/SiO2 Catalysts for n-Hexane and CO Oxidation

Two-component Co–Ce samples deposited onto SiO2 have been prepared, characterized and tested in the reaction of complete n-hexane and CO oxidation. It was established that cerium enhanced the catalytic activity of cobalt in the reaction of n-hexane oxidation, although this depended on the sequence of cobalt and cerium introduction. Co-impregnation of Co and Ce resulted in a close interaction between Co3O4 and CeO2 leading to more surface oxygen species available and, therefore, a better reactivity.

An Extremely Active Pt/Carbon Nano-Tube Catalyst for Selective Oxidation of CO in H2 at Room Temperature

Pt catalyst supported on carbon nano-tube (CNT) was extremely active for the selective oxidation of CO in H2 at room temperature, which was remarked contrast to the Pt supported on an active carbon (Vulcan carbon) and a graphite powder. Complete oxidation of CO was attained on a 5 wt.% Pt/CNT catalyst (0.8 g) at ca. 40 °C when the O2/CO ratio in a flow of H2 (20 mL/min) + CO (3.0 mL/min) + O2 + N2 was adjusted to be larger than 0.75 at the total flow rate of 100 mL/min. Specific activity of the Pt/CNT catalyst was explained by efficient provision of reactant molecules diffusing on CNT surface to Pt particles.