Effect of MgF2 and Al2O3 supports on the structure and catalytic activity of copper–manganese oxide catalysts

Structure and catalytic activity of double copper–manganese oxide catalysts supported on MgF₂ and Al₂O₃ have been studied. All samples were calcined at 400 °C and those supported on Al₂O₃ also at 550 and 950 °C. The properties of surface species have been characterized by low temperature adsorption of nitrogen, XRD and TPR-H₂. The catalytic activities have been tested in low-temperature CO oxidation and in NO reduction by propene. The supported oxides react with each other during calcination to form CuMn₂O₄ spinel. The spinel seems to be responsible for the catalytic activity of the double copper–manganese catalysts. The temperature of calcination changes the strength of interaction between the active phase and the supports influencing the catalytic activity.     

Low-temperature Oxidation of Carbon Monoxide on Co/ZrO2

A 10%Co/ZrO₂ catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO₂ in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO₂ oxidation reaction was calculated as E_a = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co₃O₄ is present on monoclinic ZrO₂ after the calcination of the catalyst.     

COMPARATIVE STUDY OF Ag2O/CO3O4 CATALYSTS PREPARED BY THE SOL-GEL AND CO-PRECIPITATION TECHNIQUES: CHARACTERIZATION AND CO ACTIVITY STUDIES

In this study effects of the preparation method on the characteristic properties and CO oxidation activities of Ag₂O/Co₃O₄ catalysts were investigated. Catalysts were prepared by two different methods: sol gel and co-precipitation. N₂ physisorption measurements, X-ray diffraction, and scanning electron microscopy measurements were used to characterize the catalysts. CO oxidation activity tests were carried out under 1% CO, 21% O₂, and the remainder He feed condition between 20° and 200°C. According to the N₂ physisorption measurements, catalysts prepared by the co-precipitation method have a higher surface area than the catalysts prepared by the sol-gel method. Co₃O₄ and AgCoO₂ phases were obtained from catalysts prepared by both techniques. In addition to these phases, metallic silver peaks were obtained by increasing calcination temperature. SEM micrographs of the catalysts showed that catalysts have uniform particles. Increasing the calcination temperature caused the formation of different-sized agglomerates and an increase in the gaps between agglomerates. The best activity was obtained from the Ag₂ O/Co₃ O₄ catalyst calcined at 200°C and prepared by the co-precipitation method. This catalyst gave 50% CO conversion at 106°C. The other two catalysts gave 100% CO conversion at a higher temperature of 200°C.     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.     

Comparison of CuO/Ce0.8Zr0.2O2 and CuO/CeO2 Catalysts for Low-temperature CO Oxidation

CuO/Ce_0.8Zr_0.2O₂ and CuO/CeO₂ catalysts were prepared via a impregnation method characterized by using FT-Raman, XRD, XPS and H₂-TPR technologies. The catalytic activity of the samples for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The influence of the calcination temperature and different supports on the catalytic activity was studied.     

Conversions of Methane to Synthesis Gas over Co/γ-Al2O3 by CO2 and/or O2

The goal of the paper was to investigate the effect of the catalyst precursor on the catalytic activity. For this reason, the structure, the reducibility and the reaction behavior of -Al₂O₃-supported Co (24 wt%) catalysts as a function of calcination temperature (T _c) were investigated using X-ray diffraction, temperature-programmed reduction, CO chemisorption, pulse reaction with pure CH₄, and the catalytic reactions of methane conversion to synthesis gas. Depending on T _c, one, two, or three of the following Co-containing compounds, Co₃O₄, Co₂AlO₄, and CoAl₂O₄, were identified. Their reducibility decreased in the sequence: Co₃O₄>Co₂AlO₄>CoAl₂O₄. Co₃O₄ was generated as a major phase at a T _c of 500°C and Co₂AlO₄ and CoAl₂O₄ at a T _c of 1000°C. The reduced Co/-Al₂O₃ catalysts, obtained via the reduction of the 500 and 1000°C calcined catalysts, provided high and stable activities for the partial oxidation of methane and the combined partial oxidation and CO₂ reforming of methane. They deactivated, however, rapidly in the CO₂ reforming of methane. Possible explanations for the stability are provided.     

Catalytic Oxidation of CO Over Synthesized Nickel Ferrite Nanoparticles from Fly Ash

Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe₂O₄, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 ≤ T ≤ 800 °C, impure low crystalline NiFe₂O₄ phase formed. The main impurities are FeO (OH) and Fe₂O₃ · H₂O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 °C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe₂O₄ powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe₂O₄ powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2–8.5 nm), the higher surface area (25–55 m²/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.     

Effect of CeO2 Doping on Structure and Catalytic Performance of Co3O4 Catalyst for Low-Temperature CO Oxidation

The effect of CeO₂ doping on structure and catalytic performance of Co₃O₄ catalyst was studied for low-temperature CO oxidation. The Co₃O₄ catalyst was prepared by a precipitation method and the CeO₂/Co₃O₄ catalyst was prepared by an impregnation method. Their catalytic performance had been studied with a continuous flowing micro-reactor. The results reveal that the CeO₂/Co₃O₄ catalyst exhibits much better resistance to water vapor poisoning than the Co₃O₄ catalyst for CO oxidation. The CeO₂/Co₃O₄ catalyst can maintain CO complete conversion at least 8,400 min at 110 °C with 0.6% water vapor in the feed gas, while the Co₃O₄ catalyst can maintain at 100% for only 100 min. Characterizations with XRD, TEM and TPR suggest that the CeO₂/Co₃O₄ catalyst possesses higher dispersion degree, smaller particles and larger S_BET, due to the doping of Ceria, and exists the interaction between CeO₂ and Co₃O₄, which may contribute to the excellent water resistance for low-temperature CO oxidation. Furthermore, the H₂ detected in the reactor outlet gas seems to indicate that the water–gas shift reaction is the more direct reason.     

Preparation of Co3O4/ZrO2(Y2O3) Catalyst and its Enhanced Catalytic Oxidation of CO

Yttria-stabilized zirconia powders were prepared by the sol–gel method coupled with supercritical CO₂ fluid-drying technology, using ZrOCl₂·8H₂O as the precursor, urea as the precipitant, and yttria as the stabilizer. The particles were characterized by X-ray diffraction, TEM and BET. The Co₃O₄/ZrO₂(Y₂O₃) catalysts were prepared by the impregnation method. The content of cobalt was varied from 5 to 12 wt%. The prepared catalysts were calcined at 200–500 °C and the pretreating temperature was varied from 200–400 °C. The performance of CO catalytic oxidation was tested and the catalyst with 8% Co loading, calcined at 200 °C, and with a pretreating temperature of 300 °C, showed the highest catalytic activity. The temperature for 95% CO conversion was as low as 113 °C; and, the catalyst showed both good cycling stability and excellent long-term stability.     

Phase transformation in CeO2–Co3O4 binary oxide under reduction and calcination pretreatments

The CeO₂–Co₃O₄ binary oxide was prepared by impregnation of the high surface area Co₃O₄ support (S.A. = 100m² g⁻¹) with cerium nitrate (20 wt% cerium loading on Co₃O₄). Pretreatment of CeO₂–Co₃O₄ binary oxide was divided both methods: reduction (under 200 and 400 °C, assigned as CeO₂–Co₃O₄–R200 and CeO₂–Co₃O₄–R400 and calcination (under 350 and 550 °C, assigned as CeO₂–Co₃O₄–C350 and CeO₂–Co₃O₄–C550). The binary oxides were investigated by means of X-ray diffraction (XRD), nitrogen adsorption at −196 °C, infrared (IR), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and temperature programmed reduction (TPR). The results showed that the binary oxides pretreatment under low-temperatures possessed larger surface area. The cobalt phase of binary oxides also was transferred upon the treating temperature, i.e., the CeO₂–Co₃O₄–R200 binary oxide exhibited higher surface area (S.A. = 109m² g⁻¹) and the main phase was CeO₂,Co₃O₄ and CoO. While, the CeO₂–Co₃O₄–R400 binary oxide exhibited lower surface area (S.A. = 40m² g⁻¹) and the main phase was CeO₂, CoO and Co. Apparently, the optimized pretreatment of CeO₂–Co₃O₄ binary oxide can control both the phases and surface area.     

Design of active NiCo2O4‐δ spinel catalyst for abatement of CO‐CH4 emissions from CNG fueled vehicles

Increasing number of CNG vehicles on road emits considerable amount of CO, a poisonous gas and CH₄, a greenhouse‐gas. Highly active and oxygen‐deficient NiCo₂O_4‐δ spinel and its individual metal‐oxides were synthesized by calcination of precipitated/co‐precipitated basic‐carbonates followed by calcination under different strategies of stagnant air(s), flowing air(f) and reactive calcination(RC) for total oxidation of CO‐CH₄ mixture. The catalysts were characterized by XRD, XPS, BET surface‐area, SEM‐EDX and TEM. The performance order of the catalysts for the oxidation of CO‐CH₄ mixture was as follows: NiCo_RC>NiCo_f>NiCo_s>Co_RC>Co_f>Co_s>Ni_RC> Ni_f>Ni_s. The pairing of Ni and Co in spinel‐structure together with RC produced catalyst was oxygen‐deficient highly active for total oxidation of the mixture at the lowest temperature of 350°C. The NiCo_RC was found stable under reaction‐conditions for 50h at 350°C and after four successive heating (350°C)‐cooling (35°C) cycles besides accelerated‐aging tests up to 600°C. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2632–2646, 2018     

Influence of Co3O4, Fe2O3 and SiC on microstructure and properties of glass foam from waste cathode ray tube display panel (CRT)

Abstract

In the present study, the effect of temperature and oxidising agents such as Fe₂O₃ and Co₃O₄ on physical and mechanical properties of glass foam is investigated. The glass foam is made of panel glass from dismantled cathode ray tubes and SiC as a foaming agent. In the process, powdered waste glass (mean particle size below 63 μm) in addition to 4 wt-% SiC powder (mean particle size below 45 μm) are combined with Fe₂O₃ and Co₃O₄ (0·4, 0·8 and 1·2 wt-%) have been sintered at 950 and 1050°C. The glass foamed containing 1·2 wt-% Co₃O₄ has good physical properties, with porosity more than 80% and bending strength more than 1·57±0·12 MPa. However, by adding different amounts of Fe₂O₃ in comparison with samples without iron oxide, little changes in porosity and strength are obtained.     

Morphology effects of Co3O4 on the catalytic activity of Au/Co3O4 catalysts for complete oxidation of trace ethylene

Au/Co₃O₄ catalysts with different morphologies (nanorods, nanopolyhedra and nanocubes) were successfully synthesized and evaluated for ethylene complete oxidation. We found that support morphology has a significant effect on catalytic activity, which is related to the exposed planes of different morphological Co₃O₄. HRTEM revealed the Co₃O₄-nanorods predominantly exposes {110} planes, while the dominant exposed planes of Co₃O₄-nanopolyhedra and -nanocubes are {011} and {001} planes, respectively. Compared with {011} and {001} planes, {110} planes exhibit the maximum amount of oxygen vacancies, which play a major role in ethylene oxidation. Therefore, Au/Co₃O₄-nanorods exhibits extraordinary catalytic activity, yielding 93.7% ethylene conversion at 0 °C.     

Readily processed multifunctional SiC catalytic filter for industrial emissions control

One step fabrication of SiC catalytic filter is currently limited by the mismatched calcination temperature between SiC filter (>1700°C) and the catalysts (<800°C), and the difficulty in the chemical immobilization of catalysts. Here, a SrTi_1−xCo_xO₃-SiC (STC-SiC) catalytic filter was directly fabricated from raw SiC grains and STC precursor oxides (SrCO₃, TiO₂, and Co₃O₄) via a single-step reactive thermal processing (SRTP) approach, which significantly reduced energy consumption and sintering time over 50%. Acid etching enables the active TiO₂ and Co₃O₄ nanoparticles spontaneously formed on STC catalysts in STC-SiC catalytic filter (STC-SiC-A), which induces the generation of oxygen vacancies and facilitates the adsorption and activation of O₂ and NO. The STC-SiC-A catalytic filter exhibits highly competitive NO oxidation of 60% and complete dust interception (100%) at 360°C. This work demonstrates an efficient and rapid processing technique of SiC based catalytic filters, which can also be implemented on other ceramic-based catalytic filters.     

Carbon dioxide reforming of methane to synthesis gas over hexaaluminate ANiAl11O19-delta (A = Ca, Sr, Ba and La) catalysts

A series of A‐modified hexaaluminates, ANiAl₁₁O_19-δ (A = Ca, Sr, Ba and La) as new catalysts for carbon dioxide reforming of methane to synthesis gas, were prepared by decomposition of nitrates and calcination at high temperature. Nickel ions as active component were inlayed in the hexaaluminate lattices to substitute part of Al ions. The structure and properties of these samples were characterized using XRD, XPS, TPR and TGA techniques. The series of hexaaluminates exhibited significantly catalytic activity and stability at high temperature, for instance at 780°C for 18 h, the conversion of CH₄ and CO₂ was kept over 91.0 and 93.7%, respectively, meanwhile no Ni sintering, phase transformation and catalyst deactivation due to carbon deposition were found. Besides, the modifier A in the mirror plane layer of the lattices showed different effects on reducibility and catalytic activity of transition metal Ni in the hexaaluminate lattices. This revised version was published online in July 2006 with corrections to the Cover Date.     

La(1−x)SrxCo1−yFeyO3 perovskites prepared by sol–gel method: Characterization and relationships with catalytic properties for total oxidation of toluene

La_(1−x)Sr_xCo_(1−y)Fe_yO₃ samples have been prepared by sol–gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co₃O₄ that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 °C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La³⁺ by Sr²⁺ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La_0.7Sr_0.3Co_0.8Fe_0.2O₃. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mössbauer spectroscopy. Cobalt oxidation states and the amount of O⁻ electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La³⁺ by Sr²⁺. The strong lowering of the temperature at conversion 20% for the La_0.7Sr_0.3Co_(1−y)Fe_yO₃ samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O⁻ electrophilic species for the La_0.7Sr_0.3Co_(1−y)Fe_yO₃ samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O⁻ species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn–Teller effect and Mössbauer spectroscopy evidenced the presence of Fe⁴⁺ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La_0.7Sr_0.3Co_0.8Fe_0.2O₃ sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co₃O₄ particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co₃O₄.     

Electrochemical properties of cathode materials LiNi1−y Co y O2 synthesized using various starting materials

LiNi_1−y Co _y O₂ samples were synthesized at 800 °C and 850 °C, by the solid-state reaction method, using the starting materials LiOH·H₂O, Li₂CO₃, NiO, NiCO₃, Co₃O₄ and CoCO₃. The LiNi_1−y Co _y O₂ synthesized using Li₂CO₃, NiO and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group ). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of the Co ion is smaller than that of the Ni ion. The increase in c/a shows that a two-dimensional structure develops better as the Co content increases. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C using LiOH · H₂O, NiO and Co₃O₄ exhibited a larger first discharge capacity of 162 mAh g⁻¹ than the other samples. The cycling performances of the samples with the first discharge capacity larger than 150 mAh g⁻¹ were investigated. LiNi_0.9Co_0.1O₂ synthesized at 850 °C using Li₂CO₃, NiO and Co₃O₄ showed excellent cycling performance. Samples with larger first discharge capacity will have a greater tendency for lattice destruction due to expansion and contraction during intercalation and deintercalation, than samples with smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.     

Pd/Co3O4 catalyst for CH4 emissions abatement: study of SO2 poisoning effect

A catalyst with 0.7 wt% Pd load supported over Co₃O₄ oxide was investigated in the methane oxidation by operating under CH₄/O₂ stoichiometric conditions. The effect of the noble metal addition on the activity of bare Co₃O₄ was evaluated. Samples were characterized by BET, XRD, TPR and XPS analyses. The SO₂ poisoning of Pd catalyst and Co₃O₄ was studied by performing CH₄ oxidation tests under stoichiometric conditions in SO₂ (1 ppm or 10 ppm)_. Experiments evidenced that in our conditions the low amount of SO₂ doesn’t influence the Pd behaviour, whereas in presence of 10 ppm of SO₂ some deactivation occurs that becomes more evident above 450 °C at which the catalyst doesn’t reach 100% of methane conversion. Catalytic tests performed over Co₃O₄ and the Pd supported catalyst, after a treatment at 350 °C for 15 h in 10 ppm SO₂/He, suggest that Co₃O₄ is a sulphating support, as confirmed by XPS analysis. Therefore, an important role in lowering the sulphur poisoning of Pd may be played by Co₃O₄.     

Mesoporous Co-Al oxide nanosheets as highly efficient catalysts for CO oxidation

We report mesoporous Co-Al oxide nanosheets (Co_xAl-Ns, where x denotes the Co/Al ratio in the samples) prepared by calcination of CoAl-hydrotalcite and subsequent alkaline treatment. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements show that the prepared Co-Al oxide nanosheets (Co_xAl-Ns) are very thin (10–15 nm) and exhibit high mesoporosity (3–5 nm). Catalytic CO oxidation tests reveal that the Co_xAl-Ns exhibit excellent catalytic performances at relatively low temperatures: for example, the Co_2.5Al-Ns catalyst could achieve 99% CO conversion at −98°C. Kinetic studies and experimental investigations indicate that the high activity of the Co_2.5Al-Ns sample is strongly related to the abundance of active sites associated with the large Brunauer–Emmett–Teller surface area. The Co_2.5Al-Ns catalyst also achieves full conversion of CO in tests performed with a gas mixture simulating automobile exhaust gas at 200°C. After loading the Co_2.5Al-Ns on a porous ceramic substrate, the obtained Co_2.5Al-Ns/PC shows high activity and stability in CO oxidation process. These features are potentially important for future industrial applications of these catalysts.