Adsorption of phenol,cresol isomers and benzyl alcohol from aqueous solution on activated carbon at 278, 298 and 323 K

Adsorption of phenol, o-, m-, p-cresol and benzyl alcohol has been measured from their aqueous solutions on activated carbon at 278, 298 and 323 K in their complete solubility range. An anomalous temperature dependence of adsorption of these compounds has been observed. Desorption measurements at 278 K show that the adsorption is not reversible in the lower concentration range. This behaviour, as well as the anomalous temperature dependence, has been attributed to chemical transformations which the adsorbed species undergo on the activated carbon surface. © 1998 SCI.     

Adsorption of SO2 from flowing air by alkaline-oxide-containing activated carbons

Adsorption of SO₂ under dynamic conditions from an SO₂-air mixture at 298 and 573 K on alkaline-oxide-containing activated carbons has been studied. The adsorption capacity of these samples at 298 K was, in general, lower than that in the original activated carbons and mainly governed by their microporosity accessible to benzene. However, at 573 K, the alkaline-oxide-containing activated carbons adsorbed a greater amount of SO₂ than the original activated carbon, following the order Na ≥ K > Rb. At both adsorption temperatures, part of the SO₂ adsorbed formed H₂SO₄ and Me₂SO₄, where Me = Na, K or Rb. When the SO₂ adsorption was carried out at 573 K, this gas fixed additional oxygen complexes that evolved as CO₂ under heating up to 873 K in He flow, probably by reaction of SO₂ with carbon surface atoms of a basic nature that are not able to chemisorb oxygen from the air at the same conditions.     

Study of the reaction of NOx and soot on Fe2O3 catalyst in excess of O2

This study addresses the catalytic reaction of NO_x and soot into N₂ and CO₂ under O₂-rich conditions. To elucidate the mechanism of the soot/NO_x/O₂ reaction and particularly the role of the catalyst -Fe₂O₃ is used as model sample. Furthermore, a series of examinations is also made with pure soot for reference purposes. Temperature programmed oxidation and transient experiments in which the soot/O₂ and soot/NO reaction are temporally separated show that the NO reduction occurs on the soot surface without direct participation of the Fe₂O₃ catalyst. The first reaction step is the formation of CC(O) groups that is mainly associated with the attack of oxygen on the soot surface. The decomposition of these complexes leads to active carbon sites on which NO is adsorbed. Furthermore, the oxidation of soot by oxygen provides a specific configuration of active carbon sites with suitable atomic orbital orientation that enables the chemisorption and dissociation of NO as well as the recombination of two adjacent N atoms to evolve N₂. Moreover, carbothermal reaction, high resolution transmission electron microscopy and isotopic studies result in a mechanistic model that describes the role of the Fe₂O₃ catalyst. This model includes the dissociative adsorption of O₂ on the iron oxide, surface migration of the oxygen to the contact points of soot and catalyst and then final transfer of O to the soot. Moreover, our experimental data suggest that the contact between both solids is maintained up to high conversion levels thus resulting in continuous oxygen transfer from catalyst to soot. As no coordinative interaction of soot and Fe₂O₃ catalyst is evidenced by diffuse reflectance infrared Fourier transform spectroscopy a van der Waals type interaction is supposed.     

煤表面含P侧链基团对氧分子的物理吸附机理

应用量子化学密度泛函理论研究了煤表面带有含磷基团侧链与多氧分子物理吸附机理.煤表面中的含P基团与氧分子进行吸附组成的吸附态中,含P侧链中的P37原子和C14的电子向氧分子中的氧原子转移,P原子和C原子失去的电子主要被吸附在煤表面的氧得到,其中O23和O24得到较多电子,其他的氧原子得到的电子较少.由于吸附在煤表面上的氧分子都得到了电子,导致氧分子的O-O键被削弱,键长出现了不同程度的拉长.与自由氧分子相比,吸附在煤表面的氧分子O-O键的伸缩振动频率向低波数位移.计算得到氧分子与煤表面组成的吸附态的吸附能为606.09 kJ/mol,由此可知,煤表面含P侧链易与多个氧分子发生物理吸附.     

Water adsorption and energetic properties of spark discharge soot: Specific features of hydrophilicity

Water adsorption was studied for spark discharge soot which is often used as a surrogate for atmospheric soot. Analysis by adsorption gravimetry and calorimetry showed that spark discharge soot exhibits specific features of hydrophilicity. Analysis of the isotherms and heats of water adsorption revealed the peculiarities of the mechanism of surface wetting related to significant changes in the soot microstructure. The first water adsorption/desorption cycle led to irreversible water adsorption and a decrease of the surface area available for water adsorption. Repeated water adsorption/desorption cycles demonstrated swelling phenomena related to the increase of the nitrogen surface area due to interparticle microporosity. The maximum effect of the transformation was observed under exposure to saturated water vapor following the microstructure stabilization. With decreasing temperature the amount of adsorbed water also decreased. Once emitted into the atmosphere the spark discharge soot particles will exhibit irreversible changes in surface area, porosity and hygroscopicity as a result of numerous humidity fluctuations until approaching a stable state of their microstructure due to long exposure to saturated water vapor.     

The effect of oxygen on the chemisorption on polycrystalline silver surface

The adsorption of oxygen(O₂) and the effect of oxygen on the chemisorption of water(D₂O) and hydrogen(D₂) on polycrystalline silver surface have been studied using the technique of thermal desorption spectroscopy(TDS) under ultra-high vacuum(UHV) condition. Three different states of adsorbed oxygen are observed on the surface. The adsorptions and reactions of water and hydrogen on the oxygendosed surface are strongly affected by the pre-adsorbed oxygen. Water on the oxygen-dosed surface shows a maximum desorption at 430K. During the adsorption of hydrogen on the oxygen-dosed surface, hydrogen is rapidly oxidized by a stepwise reaction in which hydrogen reacts first with O(a) to yield hydroxyl intermediate[OD(a)] and then this intermediate reacts to form water. The rate-determining step in this reaction is desorption of water.     

Zirconia supported Ru–Co bimetallic catalysts for diesel soot oxidation

Various amounts of ruthenia–cobaltate bimetallic catalyst supported on zirconia have been prepared by co-impregnation method and their catalytic activity towards soot/carbon oxidation has been evaluated using TG technique under the loose contact condition. These catalysts show good activity for carbon/soot oxidation, which is observed to be a factor of ruthenia content. The thermal stability experiments confirmed the stability of catalytic materials in air at least up to 900 °C. In this way, ruthenia can be easily dispersed on zirconia possibly through the solid solution formation, while its thermal stability can be significantly improved by introducing a transition metal namely cobalt. Formation of Ru–Co bimetallic clusters over zirconia is probably responsible for its thermal stability, while dissociative adsorption of oxygen on catalyst surface appears to be responsible for their catalytic activity.     

Adsorption and reaction of NO on activated carbon in the presence of oxygen and water vapour

A study of the adsorption and reaction of NO in the presence of oxygen and water vapour on an activated carbon obtained from oil palm shells is presented. The study is based on the measurement of breakthrough curves, at temperatures between 100 and 150 °C, and on the subsequent thermal desorption in a fix bed reactor. The concentration of the gas components, NO, O₂ and H₂O, corresponds to a simulation of a flue gas in a coal fired power plant. The experimental results show that the reactions on this system include the simultaneously adsorption, reduction and catalytic oxidation of NO together with the adsorption of created NO₂. During desorption NO₂ reacts to NO through a reductive desorption process. An acceleration of the NO oxidation occurs when the saturation level of the adsorbed NO is reached, resulting in a maximum on the breakthrough curve. Different adsorbed NO species are formed during the process: one thermal unstable NO, and three thermal stable NO species, NO₂, NO and (NO)₂ dimers, respectively.     

Development of a transient kinetic model for the CO oxidation by O2 over a Pt/Rh/CeO2/γ-Al2O3 three-way catalyst

A transient kinetic model was developed for the CO oxidation by O₂ over a Pt/Rh/CeO₂/γ-Al₂O₃ three-way catalyst. The experiments which were modelled consisted of periodically switching between a feed stream containing 0.5 mol% CO in helium and a feed stream containing 0.5 mol% O₂ in helium, with a frequency from 0.1 to 0.25 Hz, in the temperature range 393–433 K. These temperatures are representative for cold start conditions. The transient experiments yield information about the reaction mechanism. A transient kinetic model based on elementary reaction steps was developed which describes the experimental data in the above mentioned range of experimental conditions adequately. The kinetic model consists of two monofunctional and one bifunctional contribution. The first monofunctional reaction path comprises competitive adsorption of CO and O₂ on the noble metal surface followed by a surface reaction. The second monofunctional reaction path consists of CO adsorption on an oxygen atom adsorbed on the noble metal surface, followed by a reaction to CO₂. The bifunctional reaction path involves a reaction between CO adsorbed on the noble metal surface and oxygen from ceria at the noble metal/ceria interface. Also, reversible adsorption of carbon dioxide on the support is taken into account. The kinetic parameters, i.e. preexponential factors and activation energies for the different elementary reaction steps, and the oxygen storage capacity were estimated using multi-response non-linear regression analysis of the oxygen, carbon monoxide and carbon dioxide outlet concentrations.     

Physisorption of hydrogen in single-walled carbon nanotubes

The interaction of hydrogen with single-walled carbon nanotubes (SWNTs) was analysed. A SWNT sample was exposed to D₂ or H₂ at a pressure of 2 MPa for 1 h at 298 or 873 K. The desorption spectra were measured by thermal desorption spectroscopy (TDS). A main reversible desorption site was observed throughout the range 77 to 320 K. The activation energy of this peak at about 90 K was calculated assuming first-order desorption. This corresponds to physisorption on the surface of the SWNTs (19.2±1.2 kJ/mol). A desorption peak was also found for multi-walled carbon nanotubes (MWNTs), and also for graphite samples. The hydrogen desorption spectrum showed other small shoulders, but only for the SWNT sample. They are assumed to originate from hydrogen physisorbed at sites on the internal surface of the tubes and on various other forms of carbon in the sample. The nanosized metallic particles (Co:Ni) used for nanotube growth did not play any role in the physisorption of molecular hydrogen on the SWNT sample. Therefore, it is concluded that the desorption of hydrogen from nanotubes is related to the specific surface area of the sample.     

Oxygen chemisorption on microporous carbons: An analysis of experimental data

Chemisorption of oxygen on Spherocarb has been performed to determine the surface oxide formation and the initial adsorption rate of Spherocarb, at the temperature range of 360 K to 851 K and oxygen pressure range of 0.05 to 1 atmosphere respectively. The maximum amount of oxygen adsorbed is estimated to occupy 91.8 m²/gC or 10% of the total surface area (TSA). The rate of chemisorption of oxygen on Spherocarb is very rapid in the beginning but it slows down with coverage. The initial oxygen chemisorption data can be linearized when plotted as amount adsorbed vs.ln (time). The data can be fitted to the integrated form of the Elovich equation, which is q= l/b*ln(l + abt) where q is the amount adsorbed and a and b are constants. This equation is applicable to the adsorption data for a wide variety of systems. A study of the variation of oxygen up-take with temperature during the first minutes of chemisorption for Spherocarb has suggested that chemisorption is the rate-controlling process initially while diffusion of oxygen and the desorption of oxidation products rapidly assume control of the oxidation rate. The experimental results show that oxygen chemisorption has an activation energy between 12 Kcal/mole and 25 Kcal/mole. It can be modeled using the Elovich equation and the initial amount chemisorbed increases in direct proportion to carbon conversion.     

SQD201树脂对钒的吸附-解吸行为及机理

通过静态吸附-解吸实验研究了SQD201树脂吸附-解吸钒的交换平衡和动力学特性,考察了pH值、温度和溶液浓度对离子交换过程的影响. 结果表明,在298 K、pH=2.0、溶液浓度为0.040 mol/L条件下,SQD201树脂的静态饱和吸附量为573.80 mg/g;钒在SQD201树脂上的吸附是吸热过程,符合Langmuir等温吸附方程. 吸附和解吸过程主要受颗粒扩散控制,吸附过程的表观活化能为20.41 kJ/mol,解吸表观活化能为22.21 J/mol. 吸附机理分析表明,SQD201树脂主要吸附的钒阴离子为H2V10O284-,H2V10O284-与树脂的理论摩尔比为1:4.     

Adsorption and Reactivity of CO2 on Potassium-Covered Re(001)

The interaction of CO₂ with potassium-covered Re(001) has been investigated. This system has been studied by means of work function (Δϕ), optical second harmonic generation (SHG), and temperature-programmed desorption (TPD) measurements. Strong electronic interaction between carbon dioxide and potassium is observed upon adsorption at 90 K. This is indicated by a rapid quenching of the SHG signal of K following postadsorption of CO₂, with a quenching cross section of 70 Ų. Work function change measurements are consistent with such interaction, evidenced by an undepolarization effect, namely, further decrease of the work function upon CO₂ adsorption, below the minimum obtained by pure potassium. In the presence of potassium, the dissociation probability of 0.5 ML adsorbed carbon dioxide increases from 0.5 on the clean metal surface to 0.85 on 1 ML potassium-covered Re(001), information obtained from TPD measurements following heating to 1250 K. It is concluded that a K–CO₂ surface compound is formed upon adsorption at 95 K on the potassium-covered surface.     

Water-induced effects on the adsorption on polycrystalline platinum (II. Interaction of carbon monoxide and water)

The adsorption and desorption of carbon monoxide and water as well as interaction between them on polycrystalline platinum has been studied using the technique of thermal desorption spectroscopy (TDS) under ultrahigh vacuum (UHV) conditions. A small amount of water adsorbs on the surface of the platinum at 310K and desorbs readily and steadily in the temperature range of 350-450 K. When exposure of water by more than 100 L is followed by saturation exposure of carbon monoxide, the height of carbon monoxide desorption peak appeared at 790 K becomes higher. It suggests that preadsorbed water dissociates a small part of carbon monoxide to atomic carbon and oxygen on the surface of the sample. And, interaction of water and carbon monoxide (or atomic carbon) results in the water-gas shift reaction.     

多壁碳纳米管吸附处理柴油废水的动力学特性

通过静态吸附实验研究了多壁碳纳米管(MWCNTs)对柴油废水中油的吸附特性,并与活性炭进行了比较。表明MWCNTs和活性炭对柴油的吸附量均在前10 min上升迅速60 min左右可达到吸附平衡,但MWCNTs的吸附能力远大于活性炭。在动力学分析中发现准二级动力学模型能较好地符合研究体系,且随温度的升高,吸附速率增加。根据Arrhenius公式,算得MWCNTs吸附柴油2^#的活化能(E_a)的值为14.21 kJ·mol^-1,可推断吸附应是物理吸附。利用颗粒内扩散模型发现MWCNTs吸附分外表面吸附、碳管间大空隙的内扩散和管间小空隙内扩散3阶段,而活性炭对柴油2^#的吸附分为外表面吸附和颗粒内扩散两个阶段,且受边界层的影响较大。MWCNTs对柴油的吸附存在初始吸附行为。在298 K下MWCNTs对3种柴油的吸附及在288、298和308 K下对柴油2^#的吸附,都是中等起始吸附,柴油2^#的吸附,随温度的升高,起始吸附行为增强,在318 K时吸附过程具有较强烈的起始吸附行为。     

Interaction of H (D) atoms with surfaces of glassy carbon: adsorption, abstraction, and etching

The interaction of thermal (2000 K) H and D atoms with glassy carbon (GC) surfaces was investigated in ultrahigh vacuum environment using thermal desorption and reaction kinetics mass spectroscopy. Virgin GC surfaces (not previously subjected to stationary etching by H atoms) exhibit a remarkably low reactivity with respect to adsorption of D. The saturation coverage of D on GC is about a factor of ten smaller than on (0 0 0 1) graphite surfaces (HOPG or natural single crystal). Thermal desorption spectra indicate that D atoms on virgin GC surfaces are adsorbed on distorted graphite basal planes, i.e. the recombinative desorption features of D on GC between 400 and 600 K are broadened as compared to those measured on graphite. Upon heating of D-covered virgin GC surfaces, CD₃ surface groups desorb between 500 and 1000 K. Stationary etching of GC by a flux of H atoms is most efficient around 600 K, as was previously observed on other carbon materials, a-C:H thin films and graphite, and as expected from the etching mechanism on C substrates. GC surfaces repeatedly etched by H exhibit an increasing density of C atoms located at edge sites which are capable to adsorb D via formation of spⁿ C-D bonds. D from these sites desorbs recombinatively around 830 K and competitive desorption of C₂ deuterocarbons at 780 K occurs. The graphite-like fraction of the surface is unaffected by etching. Abstraction of D on virgin GC by H exhibits the same phenomenology as on graphite: Eley-Rideal mechanism and large abstraction cross-section at small D coverages.     

Hydrogen adsorption characteristics of activated carbon

Hydrogen adsorption on activated carbons was investigated in the present works up to 100 bars at 298 K. Coconut-shell was activated by potassium hydroxide, resulting in activated carbons with different porosities. All of prepared activated carbons are microporous and show the same adsorption properties. The complete reversibility and fast kinetics of hydrogen adsorption show that most of adsorbed quantity is due to physical adsorption. A linear relationship between hydrogen adsorption capacity and pressure is obtained for the all samples regardless of their porosities. Hydrogen adsorption capacities are linear function of porosities such as specific surface area, micropore surface area, total pore volume, and micropore volume. The maximum hydrogen adsorption capacity of 0.85 wt.% at 100 bars, 298 K is obtained in these materials.     

NO在Ag-Pt双金属表面上的吸附和分解

本文在超高真空条件下，对NO在Pt(110)单晶面和Ag-Pt双金属模型催化剂表面上的吸附和分解进行了研究。结果表明，NO在Ag-Pt双金属表面的Pt活性中心分解，生成的强吸附氧物种可迁移到Ag原子表面，在低温630K下脱附，并提出了氧物种迁移模型。     

Adsorption of methane on corn cobs based activated carbon

Activated carbon was prepared with corn cobs and potassium hydroxide under optimized variables. Due to their botanical origin, corn cobs can be an excellent starting material to produce nanoporous carbon for natural gas storage. Samples with different BET surface areas were chosen to perform methane adsorption experiments. Methane adsorptions on corn cob based activated carbon were studied at four different pressures (500, 1000, 1500 and 2000 psi) and two different temperatures (298 K and 323 K) in a volumetric adsorption apparatus. The volume based methane adsorption results specified an ‘increase in the methane adsorption capacities of activated carbon with increasing surface area and showed that adsorption capacity of methane depends on pressure and temperature. The highest methane storage capacity was found to be 160 (v/v) at 298 K and 1500 psi. The applications include use in the transportation of natural gas, natural gas based vehicles, and adsorption of gas from landfills.     

Intrinsic photocatalytic oxidation of the dye adsorbed on TiO2 photocatalysts by diffuse reflectance infrared Fourier transform spectroscopy

Photocatalytic oxidation of aqueous pollutants by semiconductor photocatalysts was found efficient. The overall process by which the heterogeneous photocatalysis proceeds includes: the sequence of the adsorption of reactants, surface reaction and the desorption of final products. As a result, factors such as, the presence of oxygen concentration, pH values of the aqueous solution, pore properties for photocatalyst particles all determine the rate of photodegradation. This study is to concentrate on the photocatalytic mechanisms of the intrinsic reaction occurred on the photocatalysts and the adsorbed dye in air atmosphere. Additionally, the photocatalytic activities of adsorbed dyes prepared under different pH values were also examined and the solid-state results were compared with the aqueous systems at the same pH conditions. Dark adsorption experiments at different pH conditions showed that the saturation amount of dyes adsorbed on the catalysts differs significantly. However, the solid-state photodegradation rates of adsorbed dyes on TiO₂ at various pH values only showed slightly different, which is opposite to the results obtained from the aqueous systems. This evidence reveals that the external and internal mass transport processes are rate-controlling steps that restricted the photodegradation reaction of aqueous dyes at different pH conditions. Furthermore, this investigation supports a proposed direct photocatalytic mechanism for aqueous systems that the photocatalytic oxidation always begins with the adsorption process and the adsorbed dye will then be attacked by the excited hole–electron pairs and hydroxyl radicals from TiO₂ surface to produce final products.