Effects of potassium on the chemisorption of CO2 and CO on the Mo2C/Mo(100) surface

The interaction of CO₂ with K-promoted Mo₂C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO₂ on the Mo₂C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO₂ and it induces the dissociation of CO₂ through the formation of negatively charged CO₂. Potassium adatoms also promote the dissociation of adsorbed CO over Mo₂C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Recent Advances in Poly (Amide-B-Ethylene) Based Membranes for Carbon Dioxide (CO2) Capture: A Review

Polyamide-b-ethylene (Pebax) is a promising material for membrane-based gas separation application with excellent CO₂ capturing potential. Pebax is a rubbery elastomer which offers good mechanical support with its hard crystalline phase and excellent gas transport through its amorphous polyether phase. This review article includes recent advances in Pebax based membrane synthesis, solvent selection for membrane synthesis, compatible fillers with Pebax matrix and the improved gas separation performance of the prepared membranes. The literature review shows that Pebax based membranes are a good candidate for separation of CO₂ from flue gases and can be used for commercial applications.     

EFFICIENT DESULFURIZATION IN O2/CO2 COMBUSTION: DEPENDENCE ON COMBUSTION CONDITIONS AND SORBENT PROPERTIES

Based on experiments on desulfurization, CaSO₄ decomposition, and a system approach using theoretical analysis, efficient in-furnace desulfurization in O₂/CO₂ combustion was investigated. The influence of combustion conditions and sorbent properties on system desulfurization efficiency was clarified. The global desulfurization efficiency was found to increase with O₂ purity. The global desulfurization efficiency in a dry recycle was higher than that in a wet recycle. The global efficiency of in-furnace desulfurization decreased with initial O₂ concentration. As the temperature increased, the global desulfurization efficiency increased first and then decreased due to the decomposition of CaSO₄. In the temperature range investigated, the global desulfurization efficiency in O₂/CO₂ coal combustion was much higher than that of conventional coal combustion in air. The global desulfurization efficiency decreased with sorbent size. When the particle radius decreased to one quarter, the global desulfurization efficiency doubled, becoming as high as 80%. The global desulfurization efficiency was very different among the three sorbents investigated, whether in O₂/CO₂ combustion or in conventional air combustion. The global desulfurization efficiency increased in the order of Ca(OH)₂, scallop, and limestone in O₂/CO₂ combustion, but in the order of scallop, Ca(OH)₂, and limestone in conventional air combustion. Nevertheless, all three sorbents demonstrated much higher desulfurization efficiency in O₂/CO₂ combustion than in conventional air combustion.     

Complexes in the Photocatalytic Reaction of CO(2) and H(2)O: Theoretical Studies

Complexes (H(2)O/CO(2), e-(H(2)O/CO(2)) and h(+)-(H(2)O/CO(2))) in the reaction system of CO(2) photoreduction with H(2)O were researched by B3LYP and MP2 methods along with natural bond orbital (NBO) analysis. Geometries of these complexes were optimized and frequencies analysis performed. H(2)O/CO(2) captured photo-induced electron and hole produced e-(H(2)O/CO(2)) and h(+)-(H(2)O/CO(2)), respectively. The results revealed that CO(2) and H(2)O molecules could be activated by the photo-induced electrons and holes, and each of these complexes possessed two isomers. Due to the effect of photo-induced electrons, the bond length of C=O and H-O were lengthened, while H-O bonds were shortened, influenced by holes. The infrared (IR) adsorption frequencies of these complexes were different from that of CO(2) and H(2)O, which might be attributed to the synergistic effect and which could not be captured experimentally.     

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.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

FTIR studies on the CO,CO2 and H2 co-adsorption over Ru-RuO x /TiO2 catalyst

FTIR spectra of a Ru-RuO_x/TiO₂ catalyst obtained on co-adsorption of CO, CO₂ and H₂ in the temperature range of 300–500 K were found to be the sum total of corresponding spectra observed during methanation of individual oxides. The two oxides compete for metal sites and at each temperature they reacted simultaneously to form distinct transient Ru(CO)_n type species even though the nature, the stability and the reactivity of these species were different in the two cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H₂ were bonded more strongly than those formed during CO₂ + H₂ reaction.     

Pressure swing adsorption separation of H2S/CO2/CH4 gas mixtures with molecular sieves 4A, 5A,and 13X

Pressure swing adsorption experiments were carried out for the separation of equimolar mixtures of carbon dioxide and methane containing small amounts of hydrogen sulfide, utilizing 4A, 5A, and 13X molecular sieves. High-purity methane of zero or nearly zero hydrogen sulfide concentration was produced in the adsorption stage with 13X and 5A sieves, at high product recovery rates; high-purity carbon dioxide was obtained with the same sieves in the desorption stage. Zeolite 4A was found capable of raising considerably the hydrogen sulfide concentration in the accumulated desorption product (vs. the adsorption feed) at high recovery rates too. Adsorption selectivity values derived from the experimental results for all three gas pairs were in line with some theoretical predictions and experimental data of the literature.     

Hydrogen Spillover in Ga2O3–Pd/SiO2 Catalysts for Methanol Synthesis from CO2/H2

The hydrogenation of CO₂ was investigated on Ga₂O₃-promoted Pd/SiO₂ catalyts and mechanical mixtures of Ga₂O₃/SiO₂ and Pd/SiO₂ catalysts (H₂/CO₂ = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H_s, can be generated by Pd⁰ far from Ga₂O₃, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga₂O₃-Pd/SiO₂ catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga₂O₃ surface patches boost the activity, owing to a minimized effort in the H_s supply to the latter.     

Impact of SO2 concentration on the corrosion rate of X70 steel and iron in water-saturated supercritical CO2 mixed with SO2

The corrosion behavior of X70 steel and iron in water-saturated supercritical CO₂ mixed with SO₂ was investigated using weight-loss measurements. As a comparison, the instantaneous corrosion rate in the early stages for iron in the same corrosion environment was measured by resistance relaxation method. Surface analyzes using SEM/EDS, XRD and XPS were applied to study the morphology and chemical composition of the corroded sample surface. Weight-loss method results showed that the corrosion rate of X70 steel samples increased with SO₂ concentration, while the corrosion rate increased before decreasing with SO₂ concentration for iron sample. Comparing resistance relaxation method results with weight-loss method results, it is found that the instantaneous corrosion rate of iron is much higher than the uniform corrosion rate of the iron tablet specimens which are covered with thick corrosion product films after a long period of corrosion. The corrosion product films were mainly composed of FeSO₄ and FeSO₃ hydrates. The possible reaction mechanism under such environment was also analyzed, and the electrochemical reaction between the dissolved SO₂ in the condensed water film with iron is the critical reaction step.     

Mesoporous Silica Sorbents Impregnated with Blends of Tetraethylenepentamine and Alkanolamine for CO2 Separation

Mesocellular silica foam (MSU-F) supports were functionalized via wet impregnation with various amine and alcohol compounds for use as high-capacity adsorbents for CO₂ separation. The effect of the amino, hydroxyl, and ether functional groups in the impregnating mixture on the CO₂ adsorption capacity was investigated. Chemical adsorption was controlled by the composition of the compounds, and the blending effect on the adsorption performance was dependent on the temperature. MSU-F (30 wt.%) impregnated with a mixture of tetraethylenepentamine (40 wt.%) and aminoethylethanolamine (30 wt.%) showed a high adsorption capacity of 5.4 mmol/g at 333 K for 15 kPa CO₂.     

Poly(ethylene terephthalate) nanofibers prepared by CO2 laser supersonic drawing

Poly(ethylene terephthalate) (PET) nanofibers were prepared by irradiating a PET fiber with radiation from a carbon dioxide (CO₂) laser while drawing it at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The flow velocity from the orifice was estimated by computer simulation; the fastest flow velocity was calculated to be 401 m s⁻¹ at a chamber pressure of 6 kPa. A nanofiber obtained using a laser power of 8 W and a chamber pressure of 6 kPa had an average diameter of 193 nm and a draw ratio of about 900,000. This technique is a novel method for producing nanofibers.     

A rate equation for Ca(OH)2 and CO2 reaction in a spouted bed reactor at low gas concentrations

In the present study, the carbonation reaction of hydrated lime in semi-dry condition is investigated experimentally in a laboratory-scale spouted bed reactor. Results show that for operating conditions where the concentration of CO₂ is low, the capture efficiency is raised by increasing the inlet CO₂ concentration. Additionally, because of the inconsistency between the experimental reaction rate and the calculated values based on the previous proposed equations, a new rate equation is introduced that considers the dependency of CO₂ concentration too. To validate the proposed equation, its predictions were compared with another set of experimental data.     

Modification of polycarbonate membrane by polyethylene glycol for CO2/CH4 separation

In this study, permeation of carbon dioxide (CO₂) and methane (CH₄) through the polycarbonate/polyethylene glycol (PC/PEG) blend membrane was investigated. The effect of PEG content (0–5 wt%) on the permeability and selectivity was studied. Permeability measurements were carried out at pressures of 1–7 bar and at room temperature. The membranes were characterized by Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and density measurement. The results revealed that the PC/PEG blends are miscible/partially miscible without considerable micro-phase separation. The effect of PEG content and gas pressure on the diffusion and solubility of coefficients were also investigated and analyzed. It was concluded that the most influential parameter for the permeation is the diffusion coefficient of the gases. The permeability and selectivity decrease as the operating pressure and PEG content are increased. Furthermore, the results showed that the addition of 5 wt% of PEG into PC increases the CO₂/CH₄ selectivity from 26.6 ± 0.99 to 40.9 ± 2.14 (more than 53%) at 1 bar.     

The AEROPILs Generation: Novel Poly(Ionic Liquid)-Based Aerogels for CO2 Capture

CO₂ levels in the atmosphere are increasing exponentially. The current climate change effects motivate an urgent need for new and sustainable materials to capture CO₂. Porous materials are particularly interesting for processes that take place near atmospheric pressure. However, materials design should not only consider the morphology, but also the chemical identity of the CO₂ sorbent to enhance the affinity towards CO₂. Poly(ionic liquid)s (PILs) can enhance CO₂ sorption capacity, but tailoring the porosity is still a challenge. Aerogel’s properties grant production strategies that ensure a porosity control. In this work, we joined both worlds, PILs and aerogels, to produce a sustainable CO₂ sorbent. PIL-chitosan aerogels (AEROPILs) in the form of beads were successfully obtained with high porosity (94.6–97.0%) and surface areas (270–744 m²/g). AEROPILs were applied for the first time as CO₂ sorbents. The combination of PILs with chitosan aerogels generally increased the CO₂ sorption capability of these materials, being the maximum CO₂ capture capacity obtained (0.70 mmol g⁻¹, at 25 °C and 1 bar) for the CHT:P[DADMA]Cl_30% AEROPIL.     

Grafting of polypropylene with N-cyclohexylmaleimide and styrene simultaneously using supercritical CO2

Monomer mixture of styrene (St) and N-cyclohexylmaleimide (ChMI) and initiator benzoyl peroxide (BPO) were first impregnated into isotactic polypropylene (iPP) films simultaneously using supercritical carbon dioxide (SC CO₂) as a solvent and swelling agent at 35.0 °C. The composites were obtained after the monomers were grafted onto the iPP matrix at 70 °C. The effects of various conditions, such as pressure, monomer concentration, and the molar ratio of the two monomers in the soaking process, on the composition of the composites were determined. The molar ratios of St to ChMI in the composites were estimated by Fourier transform infrared spectroscopy. The thermal properties, the morphology, and the mechanical properties of the composites were characterized by different techniques. The results demonstrated that the phase size of the grafted St-ChMI was very small and the phase boundary was very ambiguous. The composites had better thermal stability than the original iPP film. The Young's modulus and tensile strength of the film increased continuously with increasing grafting percentage. The two grafted monomers in the composites had good synergetic effect.     

Enzymatic Reactions in Near Critical CO2: The Effect of Pressure on Phenol Removal by Tyrosinase

The use of enzymes in supercritical CO₂ (SCCO₂) has received extensive attention in recent years. Biocatalysts have the advantage of substrate specificity and SCCO₂ offers several advantages over liquid solvents. This work deals with the utilization of SCCO₂ as a medium for the enzymatic removal of phenol from aqueous solutions using tyrosinase. Since the presence of oxygen is crucial for the enzyme-catalyzed oxidation, the substantial solvating power of SCCO₂ makes it a promising medium for such reactions. The conversion of phenol was higher at 10 MPa. Under near critical conditions (7 MPa, 35 °C), the addition of air at 5 × 10⁵ Pa of pressure improved phenol removal.     

CO Adsorbed Infrared Spectroscopy Study of Ni/Al2O3 Catalyst for CO2 Reforming of Methane

CO adsorbed infrared spectroscopy study was conducted in this work in order to better understand the significantly improved anti-coke performance of Ni/Al₂O₃ catalyst obtained via argon glow discharge plasma treatment. The present study revealed a significant decrease of linear to bridge (L/B) adsorbed CO for glow discharge plasma treated Ni/Al₂O₃, compared to that for untreated Ni/Al₂O₃, indicating an enhancement of close packed plane concentration. This structure change leads to lower methane turnover frequency (TOF) and better balance of carbon formation-gasification, resulting in better anti-coke property of Ni/Al₂O₃ for CO₂ reforming of methane.     

Adsorption of binary CO2/CH4 mixtures using carbon nanotubes: Effects of confinement and surface functionalization

Effect of confinement and surface functionalization in carbon nanotubes (CNTs) on the competitive adsorption of a binary CO₂/CH₄ mixture has been investigated by grand canonical Monte Carlo simulations. Adsorption using CNTs with different functionalization arrangements, different diameters, different functionalization degrees, and different functional groups, such as –COOH, –CO, –OH, –CH₃, is investigated. Effects of (a) the pore textural properties, such as pore size and accessible surface area, and (b) the gas–adsorbent interaction, especially the electrostatic interaction, are discussed. From these results, we discuss the impact that variables such as confinement and surface functionalization have on the performance for CO₂ separation.