Adsorption performance of Al-pillared bentonite clay for the removal of cobalt(II) from aqueous phase

In this research, the natural bentonite clay collected from Ashapura Clay Mines, Gujarat State, India, was utilized as a precursor to produce aluminium-pillared bentonite clay (Al-PILC) for the removal of cobalt(II) [Co(II)] ions from aqueous solutions. The original bentonite clay and Al-PILC were characterized with the help of chemical analyses, methylene blue (MB) adsorption isotherm, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR), while the thermal stability of the samples were studied using thermogravimetry (TG). Surface charge density of the samples as a function of pH was investigated using potentiometric titrations. Adsorption experiments were conducted under various conditions, i.e., pH, contact time, initial concentration, ionic strength, adsorbent dose and temperature. The most effective pH range for the removal of Co(II) ions was found to be 6.0–8.0. The maximum adsorption of 99.8% and 87.0% took place at pH 6.0 from an initial concentration of 10.0 and 25.0 mg l⁻¹, respectively. Kinetic studies showed that an equilibrium time of 24 h was needed for the adsorption of Co(II) ions on Al-PILC and the experimental data were correlated by either the external mass transfer diffusion model for the first stage of adsorption and the intraparticle mass transfer diffusion model for the second stage of adsorption. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. The Arrhenius and Eyring equations were applied to the data to determine the kinetic and thermodynamic parameters for explaining the theoretical behaviour of the adsorption process. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich and Scatchard isotherm equations and the adsorption process was reflected by Freundlich isotherm. The efficiency of the Al-PILC was assessed by comparing the results with those on a commercial ion exchanger, Ceralite IRC-50. The suitability of the Al-PILC for treating Co(II) solutions was tested using simulated nuclear power plant coolant samples. Acid regeneration was tried for several cycles with a view to recover the adsorbed Co(II) and also to restore the adsorbent to its original state.     

Catalytic wet peroxide oxidation (CWPO) of phenol over mixed (AlCu)-pillared clays

New mixed (AlCu)-pillared clays are prepared from a crude bentonite sample (H) (Tunisia deposit) by two discrete procedures: (a) a classical ‘D’ method by which Al or (Al, Cu) nitrate solutions, hydrolyzed with NaOH, are added to a 2% clay suspension and (b) a ‘P’ method where the clay powder is directly dispersed in the pillaring solution. Intercalation reactions are performed at 40°C, with an OH/(Al, Cu) molar ratio equal to 1.5 or 2 and an initial atomic percentage of copper (100 Cu/Al + Cu) of 0, 5 or 10%. Chemical analyses, XRD spectra and surface properties show that clays are intercalated after calcination at 300°C from both preparation procedures. There is increase of the Al content, d₀₀₁ and of the BET surface area, the copper content remains quite low whatever the conditions of preparation. Nevertheless, it seems that the copper content resulting from the ‘P’ method is higher. During phenol oxidation with hydrogen peroxide (CWPO reaction), the copper content and the procedure of preparation significantly influence the catalytic activity. Moreover, the very low copper solubilization proves that copper is certainly associated with alumina at the surface of the catalyst in mixed species intercalated or/and dispersed on the clay surface.     

Catalytic oxidation of VOCs on Au/Ce-Ti-O

Ce_xTi_1−xO₂ oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce_0.3Ti_0.7O₂ sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce_0.3Ti_0.7O₂ but the CO₂ selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H₂ TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation.     

铝柱撑活性白土催化合成苯甲醛乙二醇缩醛

以活性白土为原料,经过铝交联剂改性制成铝柱撑活性白土,并以此为催化剂,用于苯甲醛与乙二醇反应合成苯甲醛乙二醇缩醛。结果表明：铝柱撑活性白土是合成苯甲醛乙二醇缩醛的良好催化剂。最佳反应条件为：n（苯甲醛）∶n（乙二醇）为1∶1.8,催化剂1.2 g,带水剂甲苯15 mL,160℃搅拌回流3.5 h,收率可达86.8%。同时也考察了三种方法制备的铝柱撑活性白土对产品收率的影响,上述条件下用微波作用制备的铝柱撑活性白土催化效果最好,产品收率可达88.7%。     

Catalytic wet peroxide oxidation of phenol over Al–Cu or Al–Fe modified clays

Al–Fe or Al–Cu modified clays were prepared from two natural montmorillonites and employed in the phenol oxidation with hydrogen peroxide in water. The samples were efficient in phenol elimination under mild experimental conditions (atmospheric pressure, 293 K and small quantities of hydrogen peroxide) without considerable leaching of the metal ions. The clays modified with Fe achieved high conversions of phenol and TOC thus showing to be very selective towards the formation of CO₂ and H₂O.     

Catalytic oxidation of odorous organic acids

Emissions of volatile organic acids is a significant problem in rural communities. So far no one has considered catalytic solutions to the problem but catalytic alternatives look quite reasonable. In this paper we present the results of the first study of the oxidation of a series of odorous organic acids on copper catalysts. We find that the organic acids are easily oxidized on commercial copper on alumina catalysts. Light-off temperatures vary from 180°C for n-butyric acid to 220°C for acetic acid. The rate of oxidation of acetic and i-butyric acid show simple power law dependence on the concentrations of the reactants. In contrast, the oxidation of n-butyric, i-valeric and n-valeric acids show rates which reach a maximum at intermediate oxygen concentrations. Analysis of the data indicates that the copper can exist in two different states: a more active and a less active state.

These results provide the first evidence that catalytic processes are viable for emissions control in rural communities.     

Catalytic activity of copper and palladium based catalysts for toluene total oxidation

In this study, catalysts containing 0.5 wt.% of palladium or 5 wt.% of copper were compared towards toluene total oxidation using FAU Zeolite and ZrO₂ supports. A 0.5%Pd/NaFAU and 5%Cu/ZrO₂ were found to be promising catalysts for this reaction. Palladium presented then a better affinity for FAU zeolite and copper oxide had a better affinity for zirconia. The performances of Pd based catalysts were correlated to interaction between the active phase and the support whereas the activity of copper oxide was related to oxygen mobility property of the support leading to copper oxide particles easily reducible. Support modifications, yttrium addition for ZrO₂ and cation exchange for the zeolite FAU, still enhanced the catalytic activity. Therefore, 0.5%Pd/CsFAU and 5%Cu/Zr₉₅Y₅ samples were found to be interesting catalysts for total VOC oxidation.     

Influence of the exchanged cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs

0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na⁺, Cs⁺) and H⁺ in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na⁺, Cs⁺) and H⁺ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO₂ and H₂O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs.     

Preparation,characterization and catalytic activity in the deep oxidation of acetone of Cr,Al-pillared saponites

A natural saponite was pillared with hydroxy-aluminium, hydroxy-chromium and hydroxy-chromium–aluminium solutions. The solutions of intercalation were characterized by visible spectroscopy, showing the presence of chromium oligomers. The pillared saponites were characterized by X-ray diffraction and nitrogen adsorption. The catalytic activity of these materials in the deep oxidation of acetone has been investigated. © 1998 SCI     

Pd-Cu/凹凸棒石黏土催化剂催化CO氧化性能

以凹凸棒石黏土(APT)作载体,采用浸渍法制备双金属催化剂Pd-Cu/APT、单金属催化剂Pd/APT和Cu/APT,在连续流动微反装置上考察催化剂的CO催化氧化活性,采用N_2物理吸附/脱附、X射线粉末衍射和程序升温还原/脱附等手段对催化剂进行表征。结果表明,Pd-Cu/APT催化剂中Cu主要以CuCl形式存在,Pd高度分散与Cu之间产生了明显的相互作用,使Cu物种的还原温度大幅降低;经水蒸汽预处理增强了Pd-Cu/APT催化剂表面酸性,促进了催化活性的提高。在CO体积分数为0.5%、水蒸汽体积分数3.3%、空速6 000h^(-1)和常温反应条件下,CO转化率可达90%以上。     

负载型CeO_2/OMS-2催化剂对VOCs的催化氧化性能

采用回流法合成了OMS-2,同时以OMS-2为载体,采用浸渍法负载CeO_2制备了Ce/OMS-2催化剂,运用X射线衍射、拉曼光谱、BET、H_2-TPR和NH_3-TPD等方法对催化剂进行表征,并考察CeO_2/OMS-2催化剂催化氧化二氯甲烷和乙酸乙酯的性能。结果表明,CeO_2的加入并未改变OMS-2较好的八面体分子筛结构,CeO_2的晶粒很小且以高分散的形式存在;负载CeO_2的OMS-2催化剂比表面积都有增大趋势;随着CeO_2负载量的增加,低温和高温的还原峰都先向低温方向偏移再向高温方向偏移;随着CeO_2负载量的增加,高温处强酸性峰先向低温方向偏移再向高温方向偏移。反应活性结果表明,CeO_2/OMS-2催化剂活性比载体OMS-2的活性好,随着铈负载量的增加,催化活性先升高再降低,其中,CeO_2负载质量分数为1.0%(1.0Ce/OMS-2)时催化剂效果最好,这可能是由于铈的加入活化了OMS-2中的氧,影响了整体催化剂的酸性,进而影响反应性能。     

Kinetic and isothermal studies of lead ion adsorption onto bentonite

The use of bentonite for the removal of Pb(II) from aqueous solutions for different contact times, pH of suspension, and initial concentration of Pb and particle sizes of absorbent was investigated. Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto bentonite involved fast and slow processes. The adsorption mechanisms in the lead/bentonite system followed pseudo-second-order kinetics with a significant contribution of film diffusion. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms and the Langmuir model represented the adsorption process better than the Freundlich model. The maximum adsorption capacity of Pb(II) onto natural bentonite was 78.82 mg g^− 1.     

Evaluation of the performance of catalytic oxidation of VOCs by a mixed oxide at a semi‐pilot scale†

Volatile organic compounds (VOCs) are one of the main contributors to air pollution. To reduce anthropogenic emissions, it is necessary to improve existing techniques such as catalytic oxidation through the development of new cost‐effective catalysts. Although many studies deal with the development and testing of new materials, most are performed at laboratory scale, of which only a few study mixtures of VOCs. To assess their viability for industrial applications, further tests are required, namely, mixture tests at intermediate scale in relevant environment and extrapolated on an industrial scale. In this work, the catalytic performance of a new mixed oxide Co‐Al‐Ce was investigated towards the oxidation of the n‐butanol and toluene on a semi‐pilot scale (TRL 4). Single component and mixture experiments were performed for several concentrations at a fixed flow rate. A commercial catalyst Pd/γ‐Al₂O₃ was used as the benchmark to evaluate the performance of the mixed oxide. The Co‐Al‐Ce catalyst enables complete oxidation of n‐butanol at the same temperature as the reference catalyst. Moreover, it provides a better selectivity for n‐butanol, while providing an equivalent one for the oxidation of toluene. In mixtures, the presence of n‐butanol promotes the oxidation of toluene for both catalysts but more significantly for the Co‐Al‐Ce catalyst. The presence of toluene inhibits the oxidation of n‐butanol for the Co‐Al‐Ce and promotes it for high conversions of n‐butanol for the Pd/γ‐Al₂O₃ catalyst.     

Adsorption of malachite green onto bentonite: Equilibrium and kinetic studies and process design

The adsorption of malachite green onto bentonite in a batch adsorber has been studied. The effects of contact time, initial pH and initial dye concentration on the malachite green adsorption by the bentonite have been studied. Malachite green removal was seen to increase with increasing contact time until equilibrium and initial dye concentration, and the adsorption capacity of bentonite was independent of initial pH in the range 3–11. Four kinetic models, the pseudo first- and second-order equations, the Elovich equation and the intraparticle diffusion equation, were selected to follow the adsorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and correlation coefficients, for each kinetic equation were calculated and discussed. It was shown that the adsorption of malachite green onto bentonite could be described by the pseudo second-order equation. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich equations. Adsorption of malachite green onto bentonite followed the Langmuir isotherm. The thermodynamic parameters, such as ΔH, ΔS and ΔG, were also determined and evaluated. A single stage batch adsorber was designed for different adsorbent mass/treated effluent volume ratios using the Langmuir isotherm.     

Catalytic oxidation of nitric oxide over modified carbide slag: Experimental and theoretical studies

In this work, experimental and theoretical methods were used to investigate the catalytic effect of K₂O on NO oxidation. Experimental results indicated that K₂O was the main active component. It enhanced the removal of NO and decreased the reaction temperature. Theoretical results indicated that the K₂O (001)-O surface was more suitable for the adsorption of NO and O₂. Also, NO and O₂ on the Ca(OH)₂ surface may migrate to the K₂O surface for reaction. NO₂ was formed via the interaction of (NO)₂ and O atoms. The formation of ON NO was the key step for NO oxidation, which was more conducive to the subsequent oxidation of NO.     

Catalytic CO oxidation reaction studies on lithographically fabricated platinum nanowire arrays with different oxide supports

Deep-ultraviolet lithography has been coupled with size-reduction and nanoimprint lithography to create high-density arrays of 20-nm wide platinum nanowires supported on oxide thin films of silica, alumina, zirconia, and ceria. These nanowire arrays have been used as two-dimensional platinum model catalyst systems to study the effects of support on catalytic activity during the catalytic oxidation of carbon monoxide. Strong support dependence is seen for both reaction turnover frequency and the measured activation energy. In addition, the stability of the nanowire arrays under reaction conditions shows support dependence.     

Catalytic properties of Rh, Ni, Pd and Ce supported on Al-pillared montmorillonites in dry reforming of methane

A natural Maghnia clay was pillared by Al₁₃ and impregnated by 3–10 wt.% Me (Me = Rh, Ni, Pd, Ce) to be used as catalysts in the reforming of methane with carbon dioxide to synthesis gas. The structural and textural properties of materials calcined at 450 °C were determined by several techniques (XRD, FT-IR, ²⁷Al magic angle spinning (MAS) NMR, X-ray photoelectron spectroscopy (XPS), BET, thermogravimetric analysis (TGA)–DSC, H₂-temperature programmed reduction (TPR) and NH₃-TPR). Although impurities are present in the Al-pillared layered clay (PILC) support, most properties are close to those of pure Al-pillared Na-montmorillonite. Impregnation and calcination leads to the plugging of most micropores by clusters or microparticles of oxides. The NMR resonances of Al_VI and Al_IV specie are not modified after impregnation, and Al_VI/Al_IV ratio only varies on loading when compared to Al-PILC. Catalytic experiments show that the most active catalyst is 3% Rh/Al-PILC on which 88 mol.% of methane is converted at 650 °C with a minimum amount of carbon deposit. The conversions decrease along the 3% Rh ≈ 10% Ni > 3% Pd > 3% Ni > 3% Ce series. The H₂/CO ratio amounts to 1.1 with Rh and to 0.85 with Pd which are metallic at the temperature of reaction, but it has a lower value with Ni and Ce due to the RWGS reaction known to proceed in the presence of oxides.