Influence of the support on CO2 methanation over Ru catalysts: an FT-IR study

The hydrogenation of CO₂ to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO₂. Ru/ZSM-5 was more selective to methane than Ru/SiO₂. On the basis of FT-IR spectra of CO and CO₂ adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the methanation of carbon dioxide over a supported Ni-La2O3 catalyst

The kinetics of the methanation of carbon dioxide was investigated using an alumina supported Ni-La₂O₂ catalyst in a differential and integral reactor. In the differential reactor the molar ratio of H₂ to CO₂ was varied from 0.6 to 30. In the integral reactor the rates were measured with up to 90% conversion. Both reactor tests were carried out at temperatures between 513 and 593 K. The experimental results were described by a Langmuir-Hinshelwood type equation. The kinetics can be explained by assuming equilibrium of dissociative carbon dioxide and hydrogen adsorption, and assuming hydrogenation of surface carbon as the rate determining step.     

Rhodium-catalyzed partial oxidation of methane to CO and H2. In situ DRIFTS studies on surface intermediates

Reaction steps in the oxidation of CH₄ to CO and H₂ over a Rh(1 wt%)/-Al₂O₃ catalyst were studied using in situ DRIFTS at 973 K and 0.1 MPa. Product distribution and the resulting absorption band intensities of the respective adsorbates were strongly influenced by oxygen coverage and carbon deposits on the surface. CH₄ is dehydrogenated to carbon deposits and H₂ and is simultaneously oxidized to CO₂ and H₂O. OH surface groups in the support are involved in the CH_x conversion to CO via reforming reaction. The reaction of surface carbon with CO₂ was assumed to contribute to CO formation. Formate is a by-product of the reaction.     

Chemical reactivity of CO and CO2 at a Cu(110)-Cs surface

Carbon dioxide and carbon monoxide undergo reactive chemisorption with cesium modified Cu(110) and Cu(110)-O surfaces and via the anionic intermediate CO ₂ ^– (a) form a surface carbonate. The CO ₂ ^– (a) species was characterised by VEELS and XPS at low temperature (80 K) and the surface carbonate at 295 K. For cesium modified Cu(110) surfaces chemisorption of carbon monoxide gives rise to electron energy loss peaks (v _co) as low as 1450 cm^–1 at 295 K.     

Ni-Fe/BaTiO3-γ-Al2O3催化剂在低温条件下CO2和CH4重整中的应用

采用等体积浸渍法制备了一系列不同Ni和Fe添加量的Ni-Fe/BaTiO3/γ-Al2O3双金属催化剂,并在固定床反应装置上考察了在873～1 073 K温度范围内催化剂对CO2和CH4重整反应的催化活性。实验结果表明:Ni、Fe负载质量分数均为5.0%的Ni-Fe/BaTiO3/γ-Al2O3催化剂活性最好。通过TPR、TPD和TPO表征并与单金属催化剂Ni/BaTiO3/γ-Al2O3相比,Ni-Fe/BaTiO3/γ-Al2O3催化剂具有更高的催化活性、脱附和抗积炭性能。     

Modeling and Experimental Study of CO2 Removal by Alkanolamines in a Packed Bed

Absorption of CO₂ by monoethanolamine, diethanolamine, and triethanolamine solutions in a lab–scale packed bed tower was investigated. A model for analyzing the heat and mass transfer mechanism in the presence of reaction was developed and validated using the measured data for MEA and TEA solutions and the results were compared with the others' experimental data. The well-known correlations for determining Henry's constant, as a critical parameter in the presented model, were evaluated and it was shown that the available correlations are often limited to a narrow range of operating conditions which could limit the applicability of the available models.     

N2O Decomposition and Formation of NO x Species on Fe–ferrierite. Effect of NO and CO Addition on the Decomposition and the Role of Surface Species

The adsorption of CO and CO₂ on Pt supported on ZrO₂ and Ce/La-promoted ZrO₂ was studied using DRIFTS. The presence of both La and Ce resulted in a decrease in the adsorption of CO at room temperature after reduction at 350 °C. The reduction in the CO adsorption is ascribed to an increase in the support reducibility when La and Ce are both present. Reduction at 350 °C leads to the formation of oxygen defects in the dual promoted support which have been probed using DRIFTS to monitor CO₂ dissociation. Hydrogen assisted dissociation is demonstrated on the ZrO₂, CeZrO₂, and LaZrO₂ supports. In the absence of hydrogen, the presence of oxygen vacancies is shown to be necessary for CO₂ dissociation.     

CO2 plasma modification of high-modulus carbon fibers and their adhesion to epoxy resins

Interfacial bond strength is often a performance-limiting factor of carbon-fiber-reinforced composites. This limitation is most prevalent when higher-modulus fibers or relatively unreactive matrix resins, such as engineering thermoplastics or high-temperature thermoset resin systems, are used. Radio-frequency (RF) glow discharge plasmas are an effective means of modifying carbon-fiber surface chemical characteristics to promote adhesion. It has been previously shown that oxidizing plasmas are especially effective compared with electro-oxidative treatments for treating carbon fiber surfaces as revealed by titrations, electron spectroscopy, wetting, and inverse gas chromatography measurements. This study evaluated the effectiveness of CO₂ plasmas on two experimental high-modulus carbon/graphite fibers and correlated the plasma surface modification with interfacial adhesion in an epoxy matrix composite system. The results show that CO₂ plasma treatment increased the surface oxygen content by nearly a factor of 2 over typical electro-oxidation treatments. The increased oxygen is mainly in the form of hydroxyl, ketone, and carboxyl-like moieties. Unidirectional composites were prepared from as-received and plasma-modified versions of each type of experimental fiber. The composites containing plasma-modified filaments exhibited 1.5-3.0 times the strength of composites fabricated with untreated or electro-oxidized filaments in transverse-flexural tests. Short-beam shear strength increased by two times over those with as-produced filaments and is equivalent to that of composites containing electro-oxidized filaments.     

Calculation for the cathode surface concentrations in the electrochemical reduction of CO2 in KHCO3 solutions

This article presents a mathematical model that predicts the chemical conditions at the electrode surface during the electrochemical reduction of CO₂. Such electrochemical reduction of CO₂ to valuable products is an area of interest for the purpose of reducing green house gas emissions. In the reactions involved, CO₂ acts as both a reactant and a buffer, consequently the estimation of local concentrations at the electrode surface is not trivial and a numerical approach is required. The necessary partial differential equations (PDEs) have been set-up and solved using MATLAB. The results show the local concentrations at the electrode surface to be significantly different from the bulk concentrations under typical reported experimental conditions. The importance of buffer strength and a careful quantification of the degree of mixing produced in the experimental apparatus is demonstrated. The model has also been used to re-examine previously published data, showing that the Tafel slopes in CO₂ reduction are consistent with those reported for the simpler CO reduction system. Further, the effect of pulsed electroreduction was also modeled, showing that pulsing causes corresponding swings in local pH and CO₂ concentrations.     

A Study of the Activated Decomposition of CO2 on the Cu Component of a Cu/ZnO/Al2O3 Catalyst

The decomposition of CO₂ over the Cu component of two ZnO/Al₂O₃ supported Cu catalysts, having different Cu areas, has been studied over the temperature range 393–513 K. The time dependence of the evolution of CO from a CO₂/He stream (10% CO₂, 101 kPa) which was dosed continuously over the catalyst showed two peak maxima, the first of which moved to shorter times on raising the temperature. The activation energy for the decomposition of CO₂ on the ZnO/Al₂O₃ supported polycrystalline copper was obtained from a plot of the logarithm of the time to the peak maximum of the first peak against the reciprocal of the dosing temperature. The value so obtained was 83±10 kJ mol^-1 (catalyst A) and 86±10 kJ mol^-1 (catalyst B) for fresh catalysts reduced in H₂ at 513 K. This value fell to 49 ±4 kJ mol^-1 (catalyst A) and 55±5 kJ mol^-1 (catalyst B) after CO reduction at 473 K of the Cu which had been oxidised by the decomposition of the CO₂. This lowering of the activation energy for the second CO₂ decomposition is considered to be due to the original morphology of the Cu not being restored by reduction in CO after the oxygen-driven reconstruction of the Cu deriving from the decomposition of the CO₂.     

Do plant and soil systems contribute to global carbon cycling as a sink of CO2?

Major conclusions from our two projects focussing on carbon cycling in terrestrial ecosystems are as follows: 1) A rural system or a farmland system tends to be a source of carbon dioxide. However, it was possible to increase carbon dioxide sequestration in soil by changing soil or paddy/upland-field management systems. 2) A model simulation showed that a carbon budget in a natural forest was balanced before cutting but the large minus (source) was observed just after cutting. But the balance changed from minus to plus (sink) in 10 years after cutting. Nearly the same amounts of carbon as that stocked in the timbers before harvesting accumulated in 70-80 years after the cutting. 3) These results indicate the possibility of soils in terrestrial ecosystems as the major sink of atmospheric carbon dioxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

The reaction of CO2 with CH4 to synthesize H2 and CO over nickel-loaded Y-zeolites

Nickel metal introduced into Y-zeolite exhibited a high catalytic activity in the dehydro-genation of methane and in the hydrogenation of carbon dioxide with methane to obtain hydrogen and CO at about 850 K. The activity strongly depended on the nickel amount in NaY, and the catalytic properties were influenced by the kind of cations in the Y-zeolite. The higher CO₂ conversion was obtained over Ni supported on non-acidic zeolites.     

Primary reaction steps and active surface sites in the rhodium-catalyzed partial oxidation of methane to CO and H2

The nature of surface sites responsible for methane activation and CO_x formation on Rh catalysts for the partial oxidation of methane to syngas was investigated. The interaction of H₄ with Rh-black after oxidative and reductive pretreatments was studied applying (a) pulse experiments at reduced total pressure (10^–4 Pa) and 1013 K in the temporal-analysis-of-product (TAP) reactor and (b) in situ DRIFTS at 973 K. The saturation of the metal surface sites with oxygen was found to inhibit methane dissociation. Direct methane oxidation to CO₂ on the oxidized surface sites proposed earlier was excluded. Methane is first dissociated on reduced surface sites; the carbon species formed, then, react with surface oxygen to CO₂. Rh sites responsible for methane activation are neither related to the formation of the Rh₂O₃ nor Rh⁰. Probably the partially oxidized species (Rh⁺) or highly dispersed Rh³⁺ entities act as active surface centers for the dissociation of methane. For supported catalyst, such sites are stabilized by the support, which on the other side acts as a source of active oxygen involved in the oxidation of surface carbon and hydrogen.     

Effect of the CaO sintering on the calcination rate of CaCO3 under atmospheres containing CO2

For the calcination of CaCO₃ under CO₂‐containing atmospheres, a mathematical model taking into account the CO₂‐catalyzed sintering of the CaO product layer is developed. In this model, a modified shrinking core model is coupled with a population balance‐based sintering model. By comparing model predictions with experimental data, it is found that CO₂ strongly affects the overall calcination rate both at high temperature and CO₂ partial pressure, since under these conditions CaO densification considerably reduces the effective diffusivity of CO₂ within product layer. It is observed that for large particles, the CO₂‐catalyzed sintering of CaO can produce the “die off” phenomenon, which takes place when the reaction stops due to the blockage of pores within product layer. Finally, it was determined that limestone impurities do not significantly affect the calcination reaction under atmospheres containing CO₂, because CO₂ causes a much greater increase of the CaO sintering rate than limestone impurities do. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3638–3648, 2018     

Nanostructured ceria-based catalysts for oxydehydrogenation of ethane with CO2

Nanostructured cerium oxides, pure or doped with CaO, prepared from amorphous acetate precursors obtained by the freeze drying method, exhibit high surface areas and are active and selective catalysts for the oxydehydrogenation of ethane (ODE) using CO₂as an oxidant. The incorporation of Ca into a solid solution in the ceria framework reduces the activity but improves markedly the selectivity to ethene and the efficiency of CO₂. Under reaction conditions, the pure ceria was stable even at 1023 K, while the surface area of the Ca-containing sample decreased markedly. This change was accompanied by a drastic increase in the selectivity to ethene, allowing to obtain yields of ethene up to 22% with 91% selectivity.     

Continuous electroreduction of CO2 to formate using Sn gas diffusion electrodes

Electrochemical valorization may be a strategy for mitigating climate change, as the process allows for CO₂ to be converted into industrially useful chemicals. The aim of this work is to study the influence of key variables on the performance of an experimental system for continuous electroreduction of CO₂ to formate with a gas diffusion electrode (GDE) loaded with Sn. A 2³ factorial design of experiments at different levels of current density (j), electrolyte flow rate/electrode area ratio (Q/A ratio) and GDE Sn load was followed. Higher rates and concentrations (i.e., 1.4·10^?3 mol m^?2 s^?1 and 1348 mg L^?1 with efficiencies of approximately 70%) were obtained with GDEs than with plate electrodes. The statistical design of experiments demonstrated that the Sn load had the most significant effect on rate and efficiency. However, despite these promising results, further research is required to optimize the process. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3557–3564, 2014     

MDEA吸收CO2稳态模型的数值求解方法

The shooting method and the difference method are used for numerical simulation of CO2 absorptionwith aqueous solution of methyldiethanolamine (MDEA). It is demonstrated that these methods are available forthe steady-state model, which may be expressed as a set of differential algebraic equations (DAEs) with two-pointboundary values. This method makes it possible not only to obtain the concentration profiles for MDEA system, butalso to reveal the effect of CO2 interfacial concentration on the enhancement factor. With this numerical simulation,the mass transfer process with multicomponent diffusion and reactions can be better understood.     

Adsorption of CO2 on Zeolite 13X and Activated Carbon with Higher Surface Area

In this work, adsorption isotherms and adsorption kinetics of CO₂ on zeolite 13X and activated carbon with high surface area (AC-h) were studied. The adsorption isotherms and kinetic curves of CO₂ on the adsorbents were separately measured at 328 K, 318 K, 308 K, and 298 K and with a pressure range of 0–30 bar by means of the gravimetric adsorption method. The mass transfer constants and adsorption activation energy E_a of CO₂ on the adsorbents were estimated separately. Results showed that at very low pressure the amounts adsorbed of CO₂ on the zeolite 13X was higher than that on the AC-h, while at higher pressure, the amounts adsorbed of CO₂ on the AC-h was higher than that on the zeolite 13X since the AC-h has a larger surface area and a larger total pore volume compared to the zeolite 13X. The adsorption kinetics of CO₂ can be well described by the linear driving force (LDF) model. With the increase of temperature, the mass transfer constants of CO₂ adsorption on both samples increased. The adsorption activation energy E_a for CO₂ on the two adsorbents decreased with the increase of pressure. Furthermore, at low pressure the E_a for CO₂ adsorption on the zeolite 13X was slightly lower than that on the AC-h, while at higher pressure the E_a for CO₂ adsorption on the zeolite 13X was higher than that on the AC-h.     

Modeling of drug solubility in supercritical carbon dioxide using equation of state based on hole theory with molecular surface charge density

Equation of state based on hole theory with molecular surface charge density was developed for the modeling of drug solubility in supercritical carbon dioxide. In the hole theory, the density change of supercritical carbon dioxide can be represented by the number of holes in the system. The molecular interaction energy parameter was estimated using the interactions of segments on the molecular surface given by a quantum calculation using conductor-like screening model. The only one parameter, coordination number around a molecule was fitted to the experimental data of the drug solubility in supercritical carbon dioxide. The solubilities of the eighteen drugs in supercritical carbon dioxide were modeled by the equation of state with the molecular surface charge density. The effect of the molecular pair for the coordination number on the correlated results was investigated. It is found that the results using the fitted parameter of the solute–solute pair coordination number result in the modeling performance better than those of carbon dioxide–solute coordination number. The results of the modeling of drug solubility in supercritical carbon dioxide are compared with the experimental data. The average absolute relative deviation between the experimental and calculated results of the solubility for the drug composed of C, H and O atoms acetylsalicylic acid, benzoic acid, ferulic acid, (S)-naproxen, p-benzoquinone, propyl gallate, salicylic acid and vanillic acid is 0.38 smaller than those for compounds including N, F, I and S atoms, amical-48, benzocaine, caffeine, carbamazepine, (±)-flurbiprofen, methimazole, phenazopyridine, theobromine, theophylline and uracil, 0.59.     

Effect of Pd on Cu-Zn Catalysts for the Hydrogenation of CO2 to Methanol: Stabilization of Cu Metal Against CO2 Oxidation

A palladium–copper–zinc catalyst (PdO:CuO:ZnO=2:28:70), prepared by sequential precipitation of the respective cations, was tested in the hydrogenation of CO₂ at high pressure (conditions: 60 bar, CO₂:H₂=1:3 (molar), W/F=0.0675 kg h/m³, 453-513 K). The methanol yield was improved on using this Pd-containing catalyst at all temperatures with respect to the reference copper–zinc catalyst (CuO:ZnO=30:70). This improvement was not due to an additional effect in which palladium was acting as an independent catalytic site but was caused by a synergetic effect of Pd on the active Cu sites. This effect was explained in terms of hydrogen spillover and an increased stability against CO₂ oxidation of the surface copper. Therefore, the present contribution not only supports previous literature findings concerning the hydrogen spillover mechanism but also resulted in a complementary view regarding the role of palladium in Pd-modified CuO-ZnO-based catalysts.