Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO₂ from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO₂. Alternative catalyst-supporters including γ-Al₂O₃, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO₂, Cr₂O₃, Fe₂O₃, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al₂O₃ doped with MnO₂ can be considered as removal-effective sorbent for adsorption and oxidation of SO₂. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO₂/Al₂O₃ catalyst-sorbents. Results show that γ-Al₂O₃ combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO₂. Extra NO in flue gas can slightly enhance the capture efficiency of SO₂.     

TiO2 Supported Nano-Au Catalysts Prepared Via Solvated Metal Atom Impregnation for Low–Temperature CO Oxidation

The Ce _x Ti_1?x O₂ mixed oxides at different mole ratios (x=0.1–1.0) were prepared by co-precipitation of TiCl₄ and Ce(NO₃)₃. The structural and reductive properties of the Ce _x Ti_{1? x} O₂ were affected by calcination temperature. At x=0.1–0.3, CeTi₂O₆ phase was formed and mainly as amorphous after calcination at 650°C. At x=0.3, only CeTi₂O₆ was formed after calcination at 750°C and CeTi₂O₆ crystallized completely after calcination at 800°C. TPR analyses showed that the amount of H₂ consumption by Ce _x Ti_1?xO₂ (650°C) (except x=0.1) was greater than that by single CeO₂, and the valence of CeO₂was the lowest (+3.18) at x=0.3. CuO/Ce_0.3Ti_0.7O₂ was prepared by the impregnation method and catalytic properties were examined by means of a GC micro-reactor NO+CO reaction system, BET, TPR, XRD, XPS and NO-TPD. It was found that CuO/Ce_0.3Ti_0.7O₂ calcined at 650°C had the highest activity in NO+CO reaction with 100% NO conversion at reaction temperature of 300°C, and at 650°C Ce_0.3Ti_0.7O₂just began to crystallize. The catalytic activities were largely affected by the pre-treatment conditions. At low reduction temperature (100°C), CuO species was difficult to reduce. When high degree of reductions took place, both CuO species and Ce_0.3Ti_0.7O₂ reduced and thus a part of CuO species on the support surface would be covered. The XPS and NO-TPD analyses showed that CuO/Ce_0.3Ti_0.7O₂ had four NO absorption centers (Cu⁺, Cu²⁺(I), Cu²⁺(II) and Ce³⁺). The CuO species involving in NO+CO reaction included Cu²⁺(I) and Cu⁺, and CeO₂ species (Ce³⁺ and Ce⁴⁺).     

Reactions of iron sulphides in simulated stack gases

The rates of production and consumption of SO₂ by the reactions of O₂, SO₂, and mixtures of O₂ and SO₂ in simulated stack gases with fixed and fluidised beds of FeS prepared from pyrite were determined over the temperature range 800 to 950 °C. The rates of production of SO₂ by reaction of Fe₂O₃ with FeS in different gas systems were also determined. The rate controlling factors were derived for each reaction.     

Ordered Crystalline Mesoporous Oxides as Catalysts for CO Oxidation

Crystalline mesoporous metal oxides have attracted considerable attention recently, but their catalytic applications have rarely been studied. In this work, a series of crystalline three-dimensional mesoporous metal oxides (i.e., CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, β-MnO₂, Mn₂O₃, Mn₃O₄, NiO, and NiCoMnO₄) were prepared using the mesoporous silica KIT-6 as a hard template. These ordered mesoporous metal oxides with highly crystalline walls were characterized by PXRD, TEM, N₂ adsorption and evaluated as CO oxidation catalysts. These mesoporous materials, except for mesoporous Fe₂O₃, exhibit much higher catalytic activities than their bulk counterparts. In particular, mesoporous Co₃O₄, β-MnO₂, and NiO show appreciable CO oxidation activity below 0 °C, and the catalytic activities of mesoporous β-MnO₂, and NiO are even higher than those of their nanoparticulate counterparts with large surface areas. β-MnO₂ is particularly interesting because it combines low cost and low toxicity with high activity (T ₅₀ = 39 °C).     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).     

Direct conversion of methane to synthesis gas using lattice oxygen of CeO2–Fe2O3 complex oxides

Three kinds of complex oxides oxygen carriers (CeO₂–Fe₂O₃, CeO₂–ZrO₂ and ZrO₂–Fe₂O₃) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H₂-TPR and Raman. The XRD measurement shows that Fe₂O₃ particles well disperse on ZrO₂ surface and Ce–Zr solid solution forms in CeO₂–ZrO₂ sample. For CeO₂–Fe₂O₃ sample, only a small part of Fe³⁺ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO₂–Fe₂O₃ and CeO₂–ZrO₂ samples, respectively by H₂-TPR experiments. On the other hand, CeO₂–Fe₂O₃ shows a rather high reduction peak ascribed to the consuming of H₂ by bulk CeO₂, indicating high lattice oxygen content in CeO₂–Fe₂O₃ complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO₂–Fe₂O₃ sample shows evident methane combustion during the reducing of Fe₂O₃, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO₂–ZrO₂ complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H₂/CO ratio of 2) can be obtained over CeO₂–Fe₂O₃ oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe₂O₃ and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO₂–Fe₂O₃ complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO₂–Fe₂O₃ oxygen carrier, and that may be responsible for its favorable successive redox cycles performance.     

Preparation and characterizations of Ni-alumina,Ni-ceria and Ni-alumina/ceria catalysts and their performance in biomass pyrolysis

The catalytic activity of Ni/Al₂O₃, Ni/CeO₂, and Ni/Al₂O₃-CeO₂ catalysts of different compositions were investigated over biomass pyrolysis process. Catalysts were prepared using co-precipitation method with various compositions of nickel and support materials. Surface characterizations of the materials were evaluated using XRD, SEM, and BET surface area analysis with N₂ adsorption isotherm. XRD analysis reveals the presence of Al₂O₃, CeO₂, NiO, and NiAl₂O₄ phases in the catalysts. Paper samples used for daily writing purposes were chosen as biomass source in pyrolysis. TGA experiment was performed on biomass with and without presence of catalysts, which resulted in the decrease of initial degradation temperature of paper biomass with the influence of catalysts. In a fixed-bed reactor, untreated and catalyst mixed biomasses were pyrolyzed up to 800 °C, with a residence time of 15 min. The non-condensable gases were collected through gas bags every after 100 °C and also at 5, 10, and 15 min residence time at 800 °C, which were analyzed using TCD-GC equipment. Comparative distributions of solid, liquid and gaseous components were made. Results indicated diminished amount of tar production in presence of catalysts. 30 wt% Ni/CeO₂ catalyst yielded least amount of tar product. The least amount of CO was produced over the same catalyst. According to gas analysis result, 30 wt% Ni doped alumina sample produced maximum amount of H₂ production with 43.5 vol% at 800 °C (15 min residence time).     

Sintering of Ce,Sm, and Pr Oxide Nanorods

Synthesis of CeO₂, Pr₂O₃, and Sm₂O₃ nanorods and their sintering have been investigated. In a strongly alkaline medium, nanorods of CeO₂, Pr₂O₃, and Sm₂O₃ were prepared from trivalent salts of rare earths (Ce, Pr, Sm) via precipitation synthesis. Nanorods were formed by nanocrystallites of fibrous structure, which were produced by the mechanism of self‐arrangement of hexagonal particles of Re(III) hydroxides. The subsequent transformation of hydroxide into oxide proceeded via self‐preservation of the rod‐like structure. In CeO₂, the fibrous structure was noncohesive during thermal treatment at temperature of 500°C and higher. Regardless of the shape of the CeO₂ particles (spherical versus rod‐like), sintered ceramic was formed by equiaxial grains. The cohesion of the fibrous structure of Pr and Sm oxides was higher than in CeO₂. The rod‐like shape of the particles of Pr and Sm oxides was (partially) preserved during sintering.     

Some surface and kinetic effects of trace additions of selected metal oxides and halides on the thermodehydration of silica xerogel spheroids

A kinetic study of the sintering of silica xerogel has been carried out by following the rate of dehydration of xerogel spheroids, 2000 - 841 μ, on a thermal balance in the presence of small additions, usually 5 g. ion percent of selected metal oxides and halides. First order rate constants calculated from the classical kinetic expression were in excellent agreement with those obtained from the Avrami-Erofeev equation for nucleation and growth in the case of a monomolecular reaction. The surface areas and mercury densities of samples cooled from 900°, 850°, 800° and 500°C have been measured and X-ray powder diffraction patterns obtained for most samples in an attempt to identify phases formed by solid-solid interaction between the gel and the additives. The activation energies of the dehydration for the oxide additives, (CuO, NiO, Cr₂O₃, BeO, ZnO and Al₂O₃), did not show substantial enough differences to allow any decisive analysis to be made on the basis of established properties of the oxides. CdO was the most active oxide in xerogel dehydration and it is shown that this oxide takes part readily in solid-solid reactions with the xerogel in the vicinity of the Tamman temperature of silica. In the presence of the transition metal halides, (NiCl₂, CrCl₃, CuCl₂ and CoCl₂), hydrogen chloride was evolved from the matrix and xerogel dehydration may be accentuated by reaction of this gas with accessible surface hydroxyl groups. The addition of sodium halides showed no significant differences in dehydration rates whereas with lithium salts, the rate and amount of dehydration varied with the melting point of the additive.     

Removal of elemental mercury from simulated flue gas by cerium oxide modified attapulgite

A novel catalyst CeO₂/ATP was developed to remove Hg⁰ from coal fired gas. This is new way to use the facile, cheap and larger BET specific surface area catalyst attapulgite (ATP) as support to remove Hg⁰ from coal fired gas. The Hg⁰ removal and oxidation efficiency of CeO₂/ATP (1: 1) is up to 97.75% and 92.23% at 200 °C, respectively. We also found that ATP plays an important role in improving the catalyst activity of CeO₂/ATP, which can make CeO₂/ATP have more stable catalyst activity at broader temperature range and obtain lower optimum activity temperature. Other influencing factors, such as temperature and flue gas environment (SO₂, Cl₂, NO), are also investigated in order to get a clear understanding of the experiment. The formation mechanisms are also proposed.     

Hydrogen production via methanol steam reforming over Au/CuO,Au/CeO2, and Au/CuO–CeO2 catalysts prepared by deposition–precipitation

The production of hydrogen (H₂) with a low concentration of carbon monoxide (CO) via steam reforming of methanol (SRM) over Au/CuO, Au/CeO₂, (50:50)CuO–CeO₂, Au/(50:50)CuO–CeO₂, and commercial MegaMax 700 catalysts were investigated over reaction temperatures between 200 °C and 300 °C at atmospheric pressure. Au loading in the catalysts was maintained at 5 wt%. Supports were prepared by co-precipitation (CP) whilst all prepared catalysts were synthesized by deposition–precipitation (DP). The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM). Au/(50:50)CuO–CeO₂ catalysts expressed a higher methanol conversion with negligible amount of CO than the others due to the integration of CuO particles into the CeO₂ lattice, as evidenced by XRD, and a interaction of Au and CuO species, as evidenced by TPR. A 50:50 Cu:Ce atomic ratio was optimal for Au supported on CuO–CeO₂ catalysts which can then promote SRM. Increasing the reaction time, by reducing the liquid feed rate from 3 to 1.5 cm³ h^?1, resulted in a catalytic activity with complete (100%) methanol conversion, and a H₂ and CO selectivity of ～82% and ～1.3%, respectively. From stability testing, Au/(50:50)CuO–CeO₂ catalysts were still active for 540 min use even though the CuO was reduced to metallic Cu, as evidenced by XRD. Therefore, it can be concluded that metallic Cu is one of active components of the catalysts for SRM.     

Simultaneous desulfurization and denitrification of flue gas by pre-ozonation combined with ammonia absorption

A process of simultaneous desulfurization and denitrification of flue gas was conducted in this study. The flue gas containing 200 mg·m⁻³ NO, 1000–4000 mg·m⁻³ SO₂, 3%–9% O₂, and 10%–20% CO₂ was first oxidized by O₃ and then absorbed by ammonia in a bubbling reactor. Increasing the ammonia concentration or the SO₂ content in flue gas can promote the absorption of NO_X and extend the effective absorption time. On the contrary, both increasing the absorbent temperature or the O₂ content shorten the effective absorption time of NO_X. The change of solution pH had substantial influence on NO_X absorption. In the presence of CO₂, the NO_X removal efficiency reached 89.2% when the absorbent temperature was raised to 60 °C, and the effective absorption time can be maintained for 8 h, which attribute to the buffering effect in the absorbent. Besides, both the addition of Na₂S₂O₃ and urea can promote the NO_X removal efficiency when the absorbent temperature is 25 °C, and the addition of Na₂S₂O₃ had achieved better results. The advantage of adding Na₂S₂O₃ became less evident at higher absorbent temperature and coexistence of CO₂. In all experiments, SO₂ removal efficiency was always above 99%, and it was basically not affected by the above factors.     

Role of CeO2–ZrO2 in diesel soot oxidation and thermal stability of potassium catalyst

Potassium nitrate catalysts supported on different oxides (CeO₂, Ce_0.5Zr_0.5O₂ and ZrO₂) were prepared for diesel soot combustion. The ageing treatment was performed at 800 °C for 24 h and the catalytic activity was evaluated by a temperature-programmed oxidation technique. The results demonstrated that, compared with CeO₂ and ZrO₂, Ce_0.5Zr_0.5O₂ presented good redox properties, a high surface area and available potassium-holding capacity at an elevated temperature. For aged K/Ce_0.5Zr_0.5O₂, the combustion temperature of soot particle was 359 °C under tight contact conditions and 455 °C under loose contact conditions. Thus, ceria–zirconia mixed oxides were considered as good candidate supports for diesel soot oxidation catalysis.     

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.     

Film Formation in Binary Sol-Gel Systems

The film-forming capacity of binary systems containing Sb₂O₃, SnO₂, CeO₂, Y₂O₃, Nd₂O₃, Bi₂O₃, V₂O₅, ZnO, CuO, CdO, and Al₂O₃ are investigated. The best film-formers are Sb₂O₃ and SnO₂, whereas ZnO, CuO, CdO, and Al₂O₃ cannot produce films of optical quality. The rest of considered oxides do not impair the clarity of coatings when their molding content is 20 – 50%. A proportional dependence is established between the refractive index and the reflection coefficient of a film and the refractive indexes of oxides making parts of this film, as well as between the concentration of deposited FFS, the film-forming capacity of oxides, and the film thickness.     

Influence of Ethanol Washing in Precursor on CuO–CeO2 Catalysts in Preferential Oxidation of CO in Excess Hydrogen

In this study, influence of ethanol washing in precursor on CuO–CeO₂ catalysts in preferential oxidation of CO in excess hydrogen (PROX) was investigated. BET, FTIR and TPR techniques were used. The results showed that ethanol washing was beneficial to improve the catalytic performance of CuO–CeO₂ catalysts in the PROX. The CO conversion over CuO–CeO₂ catalysts without ethanol washing was only 85% at 190 °C, while the highest CO conversion over CuO–CeO₂ catalysts with 200 mL ethanol washing was beyond 99% at 120 °C. XRD and TPR results showed that ethanol washing depressed the growth of CuO–CeO₂ catalysts and improved the reducibility of CuO–CeO₂ catalysts. The FTIR measurement proved that the absorption water was decreased by the way of ethanol washing, indicating that the amount of the H–O–H bridge between adsorption water and precursor of CuO–CeO₂ catalysts was decreased and depressed the growth of CuO–CeO₂ catalysts.     

Phase and microstructure evolution of Sc2O3–CeO2 –ZrO2ceramics in Na2SO4 + V2O5 molten salts

In this study, the destabilization resistance of Sc₂O₃ and CeO₂ co-stabilized ZrO₂ (SCZ) ceramics was tested in Na₂SO₄ + V₂O₅ molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V₂O₅ to produce m-ZrO₂ and CeVO₄, and little ScVO₄ was detected in the Sc₂O₃-rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO₂ and m-ZrO₂ due to the mineralization effect. The Sc₂O₃-rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr⁴⁺ and Sc³⁺. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed.     

Effect of metallic oxides on thermal stability of ethylene–propylene terpolymer

Thermal stability of ethylene–propylene terpolymer (EPDM) loaded with various metallic oxides (PbO, CuO, NiO, Fe₂O₃, Cr₂O₃, TiO₂, ZrO₂) was assessed by the oxygen uptake method. The effects of 5 phr oxide of thermal aging of elastomer were investigated under isothermal (180°C) and isobaric (air at normal pressure) conditions. The influence of this was pointed out. Some mechanistic considerations on the oxidative degradation of EPDM are presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2155–2158, 2001     

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.     

Vapor Phase Ketonization of Acetic Acid on Ceria Based Metal Oxides

The activities of CeO₂, Mn₂O₃–CeO₂ and ZrO₂–CeO₂ were measured for acetic acid ketonization under reaction conditions relevant to pyrolysis vapor upgrading. We show that the catalyst ranking changed depending on the reaction conditions. Mn₂O₃–CeO₂ was the most active catalyst at 350 °C, while ZrO₂–CeO₂ was the most active catalyst at 450 °C. Under high CO₂ and steam concentration in the reactants, Mn₂O₃–CeO₂ was the most active catalyst at 350 and 450 °C. The binding energies of steam and CO₂ with the active phase were calculated to provide the insight into the tolerance of Mn₂O₃–CeO₂ to steam and CO₂.