The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

The kinetics of CO2 hydrogenation on a Rh foil promoted by titania overlayers

Submonolayer deposits of titania on a Rh foil have been found to increase the rate of CO₂ hydrogenation. The primary product, methane, exhibits a maximum rate at a TiO _x coverage of 0.5 ML which is a factor of 15 higher than that over the clean Rh surface. The rate of ethane formation displays a maximum which is 70 times that over the unpromoted Rh foil; however, the selectivity for methane remains in excess of 99%. The apparent activation energy for methane formation and the dependence of the rate on H₂ and CO₂ partial pressure have been determined both for the bare Rh surface and the titania-promoted surface. These rate parameters show very small variations as titania is added to the Rh catalyst. The methanation of CO₂ is proposed to start with the dissociation of CO₂ into CO_(a) and O_(a), and then proceed through steps which are identical to those for the hydrogenation of CO. The increase in the rate of CO₂ hydrogenation in the presence of titania is attributed to an interaction between the adsorbed CO, released by CO₂ dissociation, and Ti³⁺ ions located at the edge of TiO _x islands covering the surface. Differences in the effects of titania promotion on the methanation of CO₂ and CO are discussed in terms of the mechanisms that have been proposed for these two reactions.     

Solubility of CO2 in solid-state PET measured by pressure-decay method

The solubility of CO₂ in solid-state PET was measured using a pressure-decay method. In order to calculate the solubility of CO₂ in the amorphous region of PET, the crystallinity of solid state PET dissolved in CO₂ at different pressures and temperatures was measured by differential scanning calorimetry (DSC). The solubility increases with increasing pressure and it follows a linear relationship and obeys Henry’s law when the pressure is below 8 MPa. The effect of temperature on solubility is weak and the solubilities at different temperatures are almost the same under low pressures. At higher pressure, the solubility decreases with an increase in temperature. The solubility of CO₂ in the amorphous region of PET at 373.15 K, 398.15 K and 423.15 K was correlated with the Sanchez-Lacombe equation of state with a maximal correlation error of 6.69%. __________ Translated from Journal of East China University of Technology (Natural Science Edition), 2007, 33(4): 445–449 [译自: 华东理工大学学报(自然科学版)]     

Comparative CO2 Adsorption Analysis in Pure and Amine-Modified Composite Membranes

In this study, the CO₂ adsorption analysis in cellulose acetate–TiO₂- and cellulose acetate–3-aminopropyl-trimethoxysilane TiO₂-blended membranes was performed. The membranes were also characterized using scanning electron microscopy and Fourier transform infrared analysis techniques. The adsorption results indicated that 120 and 90°C were considered as optimized temperatures for regeneration of cellulose acetate–TiO₂ and cellulose acetate–3-aminopropyl-trimethoxysilane-modified TiO₂ membranes. The testing results revealed that adsorption capacity reached maximum at 3.0 bars. Validation of experimental results was performed by pseudo-first-order, second-order and intraparticle diffusion models. The correlation factor R² represented that the second-order model was fitted well with the experimental data. The intraparticle diffusion model represented that adsorption is not a single-step process.     

A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe

20%SrO-20%La₂O₃/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH₄ conversion and 80% C₂-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH₄O₂ molar ratio=91 and total flow rate of 100 ml/min. Addition of SrO onto La₂O₃/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH₄ conversion and C₂-selectivity. Meanwhile, the reaction temperature required to obtain the highest C₂-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO₂ added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO₂ will suppress the formation of CO₂ produced via the OCM reaction, therefore, improves the C₂-selectivity. The FT-IR spectra of CO₂ adspecies recorded at different temperatures show that CO₂ interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO₂ adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca²⁺ cations at room temperature. If the temperature is higher than 473 K, it will form on La³⁺ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca²⁺ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr²⁺ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO₂-TPD. The role of the surface basicity of the SLC catalyst is also discussed.     

Isolation of a new highly CO2 tolerant fresh water MicroalgaChlorella sp. KR-1

A fresh water microalga, which has tolerance to high concentrations of CO₂, was isolated. The KR-1 strain was identified as a genusChlorella. ThoughChlorella KR-1 showed maximum growth at 10 % (v/v) CO₂, the strain showed a good growth rate up to 50 % (v/v) CO₂. The results indicated the feasibility of the KR-1 strain for massive cultivation using condensed stack gases.     

CO2 Hydrogenation on Rh/TiO2 Previously Reduced at Different Temperatures

Hydrogenation of CO₂ was studied on 1% Rh/TiO₂ reduced at different temperatures. The interaction of CO₂ with the catalyst and that of the CO₂+H₂ mixture was also studied. FTIR and TPD measurements revealed that CO₂ dissociation depends on the reduction temperature of the catalyst. In the surface reaction, besides Rh carbonyl hydride, formate groups and different carbonates and surface formyl species were also formed. The surface concentration of the formyl group depended on the reduction temperature. The initial rate of CO₂ hydrogenation significantly increased with increasing reduction temperature but after some time it drastically decreased. The promotion effect of the reduction temperature was explained by the formation of oxygen vacancies on the perimeter of the Rh/TiO₂ interface, which can be re-oxidized by the adsorption of CO₂ and H₂O.     

Role of support in reforming of CH4 with CO2 over Rh catalysts

The reforming of CH₄ with CO₂ over supported Rh catalysts has been studied over a range of temperatures (550–1000 K). A significant effect of the support on the catalytic activity was observed, where the order was Rh/Al₂O₃>Rh/TiO₂>Rh/SiO₂. The catalytic activity of Rh/SiO₂ was promoted markedly by physical mixing of Rh/SiO₂ with metal oxides such as Al₂O₃, TiO₂, and MgO, indicating a synergetic effect. The role of the metal oxides used as the support and the physical mixture may be ascribed to the promotion in dissociation of CO₂ on the surface of Rh, since the CH₄ + CO₂ reaction is first order in the pressure of CO₂, suggesting that CO₂ dissociation is the rate-determining step. The possible model of the synergetic effect was proposed.     

A Fourier-transform infrared study of CO2 and CO2/H2 interactions with caesium-doped copper catalysts

FTIR spectra are reported of CO₂ and CO₂/H₂ on a silica-supported caesium-doped copper catalyst. Adsorption of CO₂ on a “caesium”/silica surface resulted in the formation of CO₂ ⁻ and complexed CO species. Exposure of CO₂ to a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving bands at 1550, 1510, 1365 and 1345 cm⁻¹. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and H₂, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial sites appeared to exhibit unusual adsorption properties.     

Preparation and characterization of gel polymer electrolyte based on PVA-K2CO3

ABSTRACT

In this study, electrolyte materials were synthesized by mixing a highly conducting salt (K₂CO₃) with the poly(vinyl alcohol) (PVA) in different proportions (from 10 to 50 wt.%). The synthesized electrolyte was characterized using Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) for their functional groups, morphology, thermal stability, glass transition temperature (T_g ), ionic conductivity, and potential window, respectively. Characterization results show that the complex formation between PVA and K₂CO₃ salt has been established by FTIR spectroscopic study, which indicates the detailed interaction between PVA and the salts in PVA-K₂CO₃ composites while the amorphous nature of the electrolyte after incorporation of the salts has been confirmed by FESEM analysis. Similarly, TGA and DSC analysis revealed that both decomposition temperature and T_g of the synthesized electrolytes decrease with the addition of K₂CO₃ due to the strong plasticizing effect of the salt. The results confirm that the electrolytes have sufficient thermal stability for supercapacitor operation, as well as an amorphous phase to effectively deliver high ionic conductivity. The highest ionic conductivity of 4.53 × 10^?3 S cm^?1 at 373 K and potential window of 2.7 V was exhibited by PK30 (30 wt.% K₂CO₃), which can be considered as high value for solid-state electrolytes which are superior to those electrolytes from PVA salts earlier reported. The results similarly show that the prepared electrolyte is temperature-dependent as conductivity increase with increase in temperature. Based on these properties, it can be imply that the PVA-K₂CO₃ gel polymer electrolyte (GPE) could be a promising electrolyte candidate for EDLC applications. The results indicate that the PVA-K₂CO₃ as a new electrolyte material has great potential in practical applications of portable energy-storage devices.     

Preferential CO oxidation over Pt–SnO2/Al2O3 in hydrogen rich streams containing CO2 and H2O (CO removal from H2 with PROX)

The effects of reaction gases including CO₂ and H₂O and temperature on the selective low-temperature oxidation of CO were studied in hydrogen rich streams using a flow micro-reactor packed with a Pt–SnO₂/Al₂O₃ sol–gel catalyst that was initially designed and optimized for operation in the absence of CO₂ and H₂O. 100% CO conversion was achieved over the 1 wt% Pt–3 wt% SnO₂/Al₂O₃ catalyst at 110 °C using a feed composition of 1.0% CO, 1.5% O₂, 25% CO₂, 10% H₂O, 58% H₂ and He as balance at a space velocity of 24,000 cm³/(g h). CO₂ in the feed was found to decrease CO conversion significantly while the presence of H₂O in the feed increased CO conversion, balancing the effect of CO₂.     

A La2NiO4-Zeolite Membrane Reactor for the CO2 Reforming of Methane to Syngas

The La₂NiO₄-zeolite membrane was prepared by means of in situ hydrothermal synthesis. Techniques such as XRD, SEM-EDX, and BET were used to acquire information as related to the structure, morphology and the pore size distribution of the membrane. At room temperature, we observed a H₂/CH₄ separation factor of 9.2, considerably higher than the Knudsen diffusion value. With the simultaneous separation of CO and H₂ in the membrane reactor, both CO₂ and CH₄ conversions were enhanced in the CH₄/CO₂ reforming reaction.     

Hydrotalcites for adsorption of CO2 at high temperature

Adsorption of carbon dioxide by hydrotalcites was investigated by using a gravimetric method at 450 ‡C. Hydrotalcites possessed higher adsorption capacity of CO₂ than other basic materials such as MgO and Al₂O₃. Two different preparation methods of hydrotalcite with varying Mg/Al ratio were employed to determine their effects on the adsorption capacity of CO₂. In addition, varying amounts of K₂CO₃ were impregnated on the hydrotalcite to further increase its adsorption capacity of CO₂. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 showed the most favorable adsorption-desorption pattern with high adsorption capacity of CO₂. K₂CO₃ impregnation on the hydrotalcite increased the adsorption capacity of CO₂ because it changed both the chemical and the physical properties of the hydrotalcite. The optimum amount of K₂CO₃ impregnation was 20 wt%. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 and 20 wt% K₂CO₃ impregnation has the highest adsorption capacity of CO₂ with 0.77 mmol CO₂/g at 450 ‡C and 800 mmHg.     

Kinetic modeling of storage and reduction with different reducing agents (CO, H2, and C2 H4) on a Pt–Ba/-Al2O3 catalyst in the presence of CO2 and H2O

In this paper a global reaction kinetic model is used to understand and describe the NO_x storage/reduction process in the presence of CO₂ and H₂O. Experiments have been performed in a packed bed reactor with a Pt–Ba/γ-Al₂O₃ powder catalyst (1 wt% Pt and 30 wt% Ba) with different lean/rich cycle timings at different temperatures (200, 250, and ) and using different reductants (H₂, CO, and C₂H₄). Model simulations and experimental results are compared. H₂O inhibits the NO oxidation capability of the catalyst and no NO₂ formation is observed. The rate of NO storage increases with temperature. The reduction of stored NO with H₂ is complete for all investigated temperatures. At temperatures above , the water gas shift (WGS) reaction takes place and H₂ acts as reductant instead of CO. At , CO and C₂H₄ are not able to completely regenerate the catalyst. At the higher temperatures, C₂H₄ is capable of reducing all the stored NO, although C₂H₄ poisons the Pt sites by carbon decomposition at . The model adequately describes the NO breakthrough profile during 100 min lean exposure as well as the subsequent release and reduction of the stored NO. Further, the model is capable of simulating transient reactor experiments with 240 s lean and 60 s rich cycle timings.     

CO2, N2 gas sorption and permeation behavior of chitosan membrane

The sorption equilibria for CO₂ and N₂ in dry chitosan membrane at 20 and 30 ‡C were measured by a pressure decay method. The steady-state permeation rates for CO₂ and N₂ in dry and wet (swollen with water vapor) chitosan membranes at 20 and 30 ‡C were measured by a variable volume method. The sorption equilibrium for N₂ obeyed Henry’s law, whereas that for CO₂ was described apparently by a dual-mode sorption model. This non-linear sorption equilibrium for CO₂ could be interpreted by the interaction of sorbed CO₂ with the chitosan matrix expressed as a reversible reaction. The logarithm of the mean permeability coefficient for CO₂ in dry chitosan membrane increased linearly with upstream gas pressure. A linear increase of the logarithmic mean permeability coefficient for CO₂ with the pressure could be interpreted in terms of a modified free-volume model. The mean per-meability coefficient for N₂ in dry chitosan membrane only slightly increased with upstream gas pressure. The per-meabilities for CO₂ and N₂ in wet chitosan membrane increased by 15 to 17 times and 11 to 15 times, respectively, as compared to those in the dry membrane.     

N-containing activated carbons for CO2 capture

A series of SK-activated carbons were prepared by carbonising soya beans in the presence of KOH as activation agent. Different activation temperatures were applied to study the influence of preparation conditions on the surface properties of the carbons and their CO₂ adsorption capacity. It was found that the CO₂ adsorption capacity is directly related to the nature of surface basic N-containing groups and that the highest CO₂ adsorption capacity value was 4.24 mmol/g under 25°C and 1 atm.     

A CO2-switchable amidine monomer: synthesis and characterization

Smart system employed CO₂ gas as new trigger has been attracting enormous attention in recent years, but few monomers that are capable of switching their hydrophobicity/hydrophility upon CO₂ stimulation have been reported. A novel CO₂ responsive monomer, 4-vinylbenzyl amidine, is designed and synthesized in this work with N,N-dimethylacetamide dimethyl acetal and 4-vinylbenzyl amine that is prepared through the Gabriel reaction. In bi-phase solvent of n-hexane and water, the monomer dissolves in n-hexane first and then transforms into water upon the CO₂ treatment, indicating a hydrophobic to hydrophilic transition. This transformation is demonstrated as reversible by monitoring the conductivity variation of its wet dimethyl formamide solution during alternate bubbling/removing CO₂. The protonation of 4-vinylbenzyl amidine upon CO₂ treatment is demonstrated by ¹H NMR which also accounts for the dissolubility change. The reversible addition-fragmentation chain-transfer polymerization of this monomer is also performed, finding the reaction only occurs in glacial acetic acid. The reason can be ascribed to the different radical structure produced in different solvent.     

CO2 Capture/Separation Control by SiO2 Nanoparticles and Surfactants

In this study, the performance enhancement of CO₂ capture and separation by the SiO₂ nanoparticles and surfactants is evaluated. The main objectives are to test the dispersion stability of nanofluids (DI water with nanoparticles and surfactants), to quantify the effect of the nanoparticles and surfactants on the CO₂ capture and separation performance, and to find the optimum conditions of the nanoparticles and surfactants. It is found that the CO₂ capture and separation performances are enhanced up to 13.1% and 7.8% at the nanoparticle concentration of 0.01 vol%, respectively. It is concluded that nanoparticles enhance both CO₂ capture and separation rates, while the surfactants enhance the CO₂ capture rate but they interrupt the CO₂ separation rate.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

CO2 reforming and partial oxidation of methane

CO₂ reforming and partial oxidation of CH₄ were investigated on different supported noble metal and Ni catalysts. A detailed thermodynamic analysis was performed for both reactions. The observed reaction behaviour can be predicted by thermodynamics. Product selectivity is catalyst independent, the role of the catalyst is to bring the reactants to approach equilibrium. The partial oxidation is a two-stage process, total oxidation of CH₄ is followed by CO₂ and H₂O reforming of the remaining CH₄. A staged addition of O₂ to the reactor is tested and recommended. TPSR show that the catalyst surface for CO₂ reforming was highly covered with carbonaceous species of four different types; two were identified as reactive intermediates.