Mechanisms and kinetics for sorption of CO2 on bicontinuous mesoporous silica modified with n-propylamine

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.     

ToF-SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay

The sorption behavior of Ba(2+) and Co(2+) ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-A steps was performed up to a 70-A matrix depth of the clay prior to and following sorption. The results showed that Co(2+) is sorbed in slightly larger quantities than Ba(2+), with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K(+), Mg(2+), and Ca(2+) from the clay lattice was observed to accompany enrichment with Co(2+) and Ba(2+) ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba(2+) and Co(2+) ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (+/-S.D.) of Ba and Co on kaolinite surface were 0.49 +/- 0.11 and 0.61 +/- 0.19 , respectively, indicating a limited uptake capacity of natural kaolinite for both ions.     

KOH改性对TiO2结构及其负载金催化剂CO氧化反应活性的影响

以不同浓度KOH处理钛酸丁酯水解产物得到KOH改性TiO2载体.使用N2吸附、热重-差热分析-示差扫描量热、X射线粉末衍射、紫外可见漫反射光谱、透射电镜及X射线光电子能谱研究了KOH对TiO2结构、形貌的影响.结果表明,较低浓度的KOH对TiO2有较显著的改性效果,改变了TiO2的电子结构.对KOH-TiO2负载的金催...     

Tuning of gate opening of an elastic layered structure MOF in CO2 sorption with a trace of alcohol molecules

It is important to tune the sorption behavior of metal-organic framework (MOF) materials. Ethanol treatment on the hydrated form of [Cu(bpy)(2)(BF(4))(2)], which is a representative flexible MOF showing the fascinating gate phenomenon on CO(2) sorption, induces an easier dehydration and a significant decrease in the CO(2) gate pressure. The results of IR, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements indicated that water molecules in the lattice of the hydrated form can be removed even at room temperature after the ethanol treatment and the basic 2D layered structure remains with a slight interlayer expansion. The results of thermogravimetric (TG) and gas chromatograph/mass spectrometry (GC/MS) analyses and of CO(2) sorptions indicated that the change of the gate phenomenon was caused by a trace of residual ethanol molecules included in the structure. Similar phenomena were observed on alcohols with different polarity and molecular size.     

Na 掺杂对硅酸锂吸收CO2性能的影响

通过高温固相反应法, 在添加不同比例Na2CO3的条件下, 合成出一系列可在高温500～750 ℃之间直接吸收CO2的硅酸锂材料. 利用扫描电子显微镜、X射线粉末衍射仪分别观察和评价了合成材料的表面形貌与结构特征, 用热重分析仪测量了硅酸锂材料的CO2吸收性能. 实验结果表明, 通过适量Na元素的掺杂, 能够提高硅酸锂材料吸收CO2的性能, 当Na2CO3的添加量x=0.02时, 合成的硅酸锂材料在CO2气氛下, 于700 ℃恒温保持约15 min即可达到吸收平衡, 材料的吸收量为(46±0.6)%(w), 与未经掺杂的材料相比, 吸收容量有所提高. 此外, 气氛中CO2的浓度对材料吸收CO2的速率有较大影响.     

Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite

New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 400 and 520 degrees C were measured on a sample of potassium-carbonate-promoted hydrotalcite, which was a reversible chemisorbent for CO(2). The equilibrium chemisorption isotherms were Langmuirian in the low-pressure region (p(CO(2)) < 0.2 atm) with a large gas-solid interaction parameter. The isotherms deviated from Langmuirian behavior in the higher pressure region. A new analytical model that simultaneously accounted for Langmuirian chemisorption of CO(2) on the adsorbent surface and additional reaction between the gaseous and sorbed CO(2) molecules was proposed to describe the measured equilibrium data. The model was also capable of describing the unique loading dependence of the isosteric heat of chemisorption of CO(2) reported in the literature. The column breakthrough curves for CO(2) sorption from inert N(2) on the chemisorbent could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The CO(2) mass-transfer coefficients were (i) independent of feed gas CO(2) concentration in the range of the data at a given temperature and (ii) a weak function of temperature. The ratio of the mass-transfer zone length to the column length was very low due to highly favorable CO(2) sorption equilibrium.     

CO_2 residual concentration of potassium-promoted hydrotalcite for deep CO/CO_2 purification in H_2-rich gas

Elevated-temperature pressure swing adsorption is a promising technique for producing high purity hydrogen and controlling greenhouse gas emissions. Thermodynamic analysis indicated that the CO in H_2-rich gas could be controlled to trace levels of below 10 ppm by in situ reduction of the CO_2 concentration to less than 100 ppm via the aforementioned process. The CO_2 adsorption capacity of potassiumpromoted hydrotalcite at elevated temperatures under different adsorption(mole fraction, working pressure) and desorption(flow rate, desorption time, steam effects) conditions was systematically investigated using a fixed bed reactor. It was found that the CO_2 residual concentration before the breakthrough of CO_2 mainly depended on the total amount of purge gas and the CO_2 mole fraction in the inlet syngas.The residual CO_2 concentration and uptake achieved for the inlet gas comprising CO_2(9.7 mL/min) and He(277.6 mL/min) at a working pressure of 3 MPa after 1 h of Ar purging at 300 mL/min were 12.3 ppm and0.341 mmol/g, respectively. Steam purge could greatly improve the cyclic adsorption working capacity, but had no obvious benefit for the recovery of the residual CO_2 concentration compared to purging with an inert gas. The residual CO_2 concentration obtained with the adsorbent could be reduced to 3.2 ppm after 12 h of temperature swing at 450 °C. A new concept based on an adsorption/desorption process, comprising adsorption, steam rinse, depressurization, steam purge, pressurization, and high-temperature steam purge, was proposed for reducing the steam consumption during CO/CO_2 purification.     

Sorption equilibria of CO2/CH4 mixture on activated carbon in presence of water

The sorption isotherms of CO2 + CH4 mixtures on an activated carbon were collected in the presence of water at a temperature suitable for hydrate formation. The equilibrium composition of both phases was determined. The initial concentration of CO2 in mixtures was set at 33, 38 and 42%, and the total pressure was up to 10 MPa. CO2 hydrates were firstly formed following the increase of total pressure, and CO2 dominates the sorbed phase composition. CO2 concentration in the sorbed phase begins to decrease when the partial pressure of methane allows for the formation of methane hydrates. Competition for hydrate cavities was observed between CO2 and CH4 as reflected in the isotherm shape and phase composition at equilibrium. The formation pressure of hydrates is lower for mixtures than for pure gases, and the highest sorption capacity of each gas decreased in the mixture sorption either.     

AAS, XRPD, SEM/EDS, and FTIR characterization of Zn2+ retention by calcite, calcite-kaolinite, and calcite-clinoptilolite minerals

In this study, the sorption behavior of Zn2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the sorption capacity was enhanced with increasing amount of calcite in both types of mixtures. Under neutral-alkaline pH conditions and high loadings, the order of Zn2+ retention was observed as calcite>clinoptilolite>kaolinite. The experiments on the retention of Zn2+ by pure calcite under conditions of oversaturation showed that the uptake process proceeds via an initial adsorption mechanism (possibly ion-exchange type) followed by a slower mechanism that leads to the overgrowth of the hydrozincite phase, Zn5(OH)6(CO3)2.     

Methanation of CO over nickel: Mechanism and kinetics at high H2/CO ratios

The CO methanation reaction over nickel was studied at low CO concentrations and at hydrogen pressures slightly above ambient pressure. The kinetics of this reaction is well described by a first-order expression with CO dissociation at the nickel surface as the rate-determining step. At very low CO concentrations, adsorption of CO molecules and H atoms compete for the sites at the surface, whereas the coverage of CO is close to unity at higher CO pressures. The ratio of the equilibrium constants for CO and H atom adsorption, K(CO)/K(H), was obtained from the rate of CO methanation at various CO concentrations. K(H) was determined independently from temperature programmed adsorption/desorption of hydrogen to be K(H) = 7.7 x 10(-4) (bar(-0.5)) exp[43 (kJ/mol)/RT] and hence the equilibrium constants for adsorption of CO molecules may be calculated to be K(CO) = 3 x 10(-7) (bar(-1)) exp[122 (kJ/mol)/RT]. Furthermore, the rate of dissociation of CO at the catalyst surface was determined to be 5 x 10(9) (s(-1)) exp[-96.7 (kJ/mol)/RT] assuming that 5% of the surface nickel atoms are active for CO dissociation. The results are compared to equilibrium and rate constants reported in the literature.     

Environmentally friendly one-pot synthesis of alpha-alkylated nitriles using hydrotalcite-supported metal species as multifunctional solid catalysts

A ruthenium-grafted hydrotalcite (Ru/HT) and hydrotalcite-supported palladium nanoparticles (Pd(nano)/HT) are easily prepared by treating basic layered double hydroxide, hydrotalcite (HT, Mg(6)Al(2)(OH)(16)CO(3)) with aqueous RuCl(3)n H(2)O and K(2)[PdCl(4)] solutions, respectively, using surface impregnation methods. Analysis by means of X-ray diffraction, and energy-dispersive X-ray, electron paramagnetic resonance, and X-ray absorption fine structure spectroscopies proves that a monomeric Ru(IV) species is grafted onto the surface of the HT. Meanwhile, after reduction of a surface-isolated Pd(II) species, highly dispersed Pd nanoclusters with a mean diameter of about 70 A is observed on the Pd(nano)/HT surface by transmission electron microscopy analysis. These hydrotalcite-supported metal catalysts can effectively promote alpha-alkylation reactions of various nitriles with primary alcohols or carbonyl compounds through tandem reactions consisting of metal-catalyzed oxidation and reduction, and an aldol reaction promoted by the base sites of the HT. In these catalytic alpha-alkylations, homogeneous bases are unnecessary and the only by-product is water. Additionally, these catalyst systems are applicable to one-pot syntheses of glutaronitrile derivatives.     

Reactivity of Mg–Al hydrotalcites in solid and delaminated forms in ammonium carbonate solutions

Treatment of Mg–Al hydrotalcites (LDHs, layered double hydroxides) in aqueous (NH₄)₂CO₃ at 298 K leads to composites of dawsonite, hydrotalcite, and magnesium ammonium carbonate. The mechanism and kinetics of this transformation, ultimately determining the relative amounts of these components in the composite, depend on the treatment time (from 1 h to 9 days), the Mg/Al ratio in the hydrotalcite (2-4), and on the starting layered double hydroxide (solid or delaminated form). The materials at various stages of the treatment were characterized by inductive coupled plasma-optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetry, and nitrogen adsorption at 77 K. The progressive transformation of hydrotalcite towards crystalline dawsonite and magnesium ammonium carbonate phases follows a dissolution–precipitation mechanism. A gradual decrease of the Mg/Al ratio in the resulting solids was observed in time due to magnesium leaching in the reacting medium. Dawsonite–hydrotalcite composite formation is favored at high aluminum contents in the starting hydrotalcite, while the formation of magnesium ammonium carbonate is favored at high Mg/Al ratios. The synthetic strategy comprising hydrotalcite delamination in formamide prior to aqueous (NH₄)₂CO₃ treatment is more reactive towards composite formation than starting from the bulk solid hydrotalcite.     

Co2C上CO的程序升温脱附和程序升温表面反应研究

采用CO与金属Co在473K反应400h以上合成了Co₂C样品,采用X射线衍射、透射电镜和CO程序升温还原对样品进行了表征,并采用CO程序升温脱附和CO程序升温表面反应研究了Co₂C对CO的吸附及其加氢活化行为. 结果表明,Co₂C微观结构由体相和表面钝化层两部分组成. 表面钝化层可被CO于477K左右去除. CO在Co₂C上有2个脱附峰,其中低温脱附峰可能源于Co₂C上吸附的CO,而高温脱附峰可能对应于残留于Co₂C晶格内的CO. Co₂C上吸附的CO可与H₂反应生成醇.     

CO2 hydrogenation on a metal hydride surface

The catalytic hydrogenation of CO(2) at the surface of a metal hydride and the corresponding surface segregation were investigated. The surface processes on Mg(2)NiH(4) were analyzed by in situ X-ray photoelectron spectroscopy (XPS) combined with thermal desorption spectroscopy (TDS) and mass spectrometry (MS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). CO(2) hydrogenation on the hydride surface during hydrogen desorption was analyzed by catalytic activity measurement with a flow reactor, a gas chromatograph (GC) and MS. We conclude that for the CO(2) methanation reaction, the dissociation of H(2) molecules at the surface is not the rate controlling step but the dissociative adsorption of CO(2) molecules on the hydride surface.     

Methane reforming With CO2 to syngas over CeO2-promoted Ni/Al2O3-ZrO2 catalysts Prepared Via a direct sol-gel process

CeO2-promoted Ni/Al2O3-ZrO2 (Ni/Al2O3-ZrO2-CeO2) catalysts were prepared by a direct sol-gel process with citric acid as gelling agent. The catalysts used for the methane reforming with CO2 was studied by infrared spectroscopy (IR), thermal gravimetric analysis (TGA), microscopic analysis, X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The catalytic performance for CO2 reforming of methane to synthesis gas was investigated in a continuous-flow micro-reactor under atmospheric pressure. TGA, IR, XRD and microscopic analysis show that the catalysts prepared by the direct sol-gel process consist of Ni particles with a nanostructure of around 5 nm and an amorphous-phase composite oxide support. There exists a chemical interaction between metallic Ni particles and supports, which makes metallic Ni well dispersed, highly active and stable. The addition of CeO2 effectively improves the dispersion and the stability of Ni particles of the prepared catalysts, and enhances the adsorption of CO2 on the surface of catalysts. The catalytic tests for methane reforming with CO2 to synthesis gas show that the Ni/Al2O3-ZrO2-CeO2 catalysts show excellent activity and stability compared with the Ni/Al2O3 catalyst. The excellent catalytic activity and stability of the Ni/Al2O3-ZrO2-CeO2 are attributed to the highly, uniformly and stably dispersed small metallic Ni particles, the high reducibility of the Ni oxides and the interaction between metallic Ni particles and the composite oxide supports.     

Synthesis and characterization of single-crystal Ce(OH)CO3 and CeO2 triangular microplates

Single-crystal cerium hydroxide carbonate (Ce(OH)CO3) triangular microplates with the hexagonal phase have been successfully synthesized by a hydrothermal method at 150 degrees C using cerium nitrate (Ce(NO3)3.6H2O) as the cerium source, aqueous carbamide as both an alkaline and carbon source, and cetyltrimethylammonium bromide (CTAB) as a surfactant. Single-crystal ceria (CeO2) triangular microplates have been fabricated by a thermal decomposition-oxidation process at 650 degrees C for 7 h using single-crystal Ce(OH)CO3 microplates as the precursor. The shape of the Ce(OH)CO3 microplate was sustained after thermal decomposition-oxidation to CeO2. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TG).     

Mg-MOF-74对CO2/H2O的吸附性能

以Mg(NO₃)₂·6H₂O和2,5-二羟基对苯二甲酸为原料, 采用溶剂热法制备了金属有机骨架材料Mg-MOF-74. 利用X射线衍射(XRD)、 红外光谱(FTIR)和扫描电子显微镜(SEM)等测试手段对其结构、 形貌和性能进行了分析, 并利用自制穿透实验装置研究了产物吸附CO₂/H₂O的性能. 结果表明: 合成的样品纯度高, 结构完整, 形貌规则有序, 具有较高的CO₂吸附量. 双组分CO₂/H₂O穿透实验结果证实, 在水蒸气存在情况下, 与沸石13X相比, Mg-MOF-74仍具有较高的CO₂吸附能力, 可用于分离高湿烟道气中的CO₂.     

Electrode Potentials of Cells with an Electrolyte Based on Zirconium Dioxide in Gas Mixtures N2+ O2+ CO2+ CO: A Platinum Electrode

Steady-state potentials of various platinum electrodes are measured in cells containing electrolyte ZrO₂+ Y₂O₃(10 mol %) in the temperature range 673–773 K in binary equilibrium gas mixtures N₂+ O₂and CO + CO₂, as well as in four-component nonequilibrium gas mixtures N₂+ O₂+ CO₂+ CO containing 0–3 vol % CO and 0–10 vol % O₂. Adding CO to a gas mixture makes the electrode potential deviate from equilibrium, which is explained by chemisorption of CO on the electrode. The oxygen, which is adsorbed on platinum, interacts with CO; as a result, CO₂undergoes desorption and the surface concentration of CO drops.     

Novel Janus Cu2(OH)2CO3/CuS microspheres prepared via a Pickering emulsion route

Janus Cu2(OH)2CO3/CuS microspheres were prepared via a Pickering emulsion route for the first time. By treating the Janus Cu2(OH)2CO3/CuS microspheres with dilute hydrochloric acid, ringent Cu2(OH)2CO3/CuS core/shell microspheres and ringent CuS shells were obtained. The hatch size of the ringent CuS shells increased with the increase of the hydrophobicity of the precursor Cu2(OH)2CO3 microspheres. Scanning electron microscopy, X-ray diffraction, energy dispersion spectra, and particle size analysis were used to characterize the products thus formed.     

H2, N2, CO, and CO2 sorption properties of a series of robust sodalite-type microporous coordination polymers

H2, N2, CO, and CO2 are readily incorporated in the porous, 3D sodalitic frameworks of coordination polymers of the [ML2]n type, with M = Pd(II) or Cu(II) and HL = 2-hydroxypyrimidine or 4-hydroxypyrimidine. The metal ion and ligand functionalization modulate their sorption properties, making these materials suitable for gas storage and separation purposes.