Adsorption of Me-HEDP complexes onto gamma-Al2O3

This work studies the adsorption of Me-1-hydroxiethane-(1,1-diphosphonic acid) (HEDP) complex onto alumina in the pH range from 5.0 to 9.5. The extent of HEDP adsorption is not significatively affected by the presence of Me(II), while, HEDP has an interesting effect on Me(II) adsorption. At high surface covering, Cu(II) adsorption is enhanced at low pH reaching a maximum of 57% at pH nearly 6, however, at pH>6 a decrease about 20% in the amount of Cu(II) adsorbed takes place by the presence of HEDP. The model predicts a ternary surface complex (AlLCu(-)) to justify the increase of Cu(II) adsorbed at lower pH. At the lower pH and at high Zn(II) concentration the presence of equimolar concentration of HEDP also causes a discernible increase in the amount of Zn(II) adsorbed. At pH 5, the percentage of Zn(II) complexed with HEDP increased from negligible to 40% as the HEDP concentration increased. However, in this case the HEDP does not have a suppressor effect on the Zn(II) adsorption at the higher pH. Again, the presence of anionic-type complexation is here postulated to reach a good fit with the experimental results. The effect of HEDP over Zn(II) adsorption becomes less pronounced with the excess of surface sites. Cd(II)-HEDP solution complexes are weaker than those corresponding to Cu(II) and Zn(II), so competitive effects between surface and solution are much less significant in comparison to Cu(II)-HEDP and Zn(II)-HEDP alumina systems. So, the effect of HEDP on the Cd adsorption at low concentration and low pH is more stressed than in the case of Cu(II) and Zn(II). Overall, results indicate that the presence of HEDP in the aquatic systems could have a significant impact on the mobility and distribution of Cu(II), Zn(II) and Cd(II) in the environment.     

Solid state NMR study of acid sites formed by adsorption of SO3 onto gamma-Al2O3

Detailed structure of Br?nsted acid sites on the surface of SO3/Al2O3 catalyst has been proposed based on 1H/27Al TRAPDOR NMR results and the acidity of the catalyst has also been characterized by NMR probe molecules.     

A study of thoria on the surface of gamma-Al2O3

The dispersion of thoria on the surface of gamma-Al2O3 and the surface properties of ThO2/gamma-Al2O3 samples, as well as the influence of the loading amount of thoria on the reduction behavior of copper oxide species, have been studied using XRD, XPS, FTIR, and TPR. The results indicate that the dispersion capacity of thoria, like that of ceria, is much lower than for two other tetravalent metal oxides, zirconia and titania, and the surface adsorption amount of the carbonyl compound and H2O slightly increases with increasing thoria loading. The different thoria loadings can influence the reduction behavior of the dispersed copper oxide by comparing the TPR results of CuO/ThO2/gamma-Al2O3 samples. In addition, the lower dispersion capacities of thoria and ceria on gamma-Al2O3 are tentatively discussed by considering the structural stability of the two oxides.     

Adsorption and protonation of CO2 on partially hydroxylated gamma-Al2O3 surfaces: a density functional theory study

Adsorption and protonation of CO2 on the (110) and (100) surfaces of gamma-Al2O3 have been studied using density functional theory slab calculations. On the dry (110) and (100) surfaces, the O-Al bridge sites were found to be energetically favorable for CO2 adsorption. The adsorbed CO2 was bound in a bidentate configuration across the O-Al bridge sites, forming a carbonate species. The strongest binding with an adsorption energy of 0.80 eV occurs at the O3c-Al5c bridge site of the (100) surface. Dissociation of water across the O-Al bridge sites resulted in partially hydroxylated surfaces, and the dissociation is energetically favorable on both surfaces. Water dissociation on the (110) surface has a barrier of 0.42 eV, but the same process on the (100) surface has no barrier with respect to the isolated water molecule. On the partially hydroxylated gamma-Al2O3 surfaces, a bicarbonate species was formed by protonating the carbonate species with the protons from neighboring hydroxyl groups. The energy difference between the bicarbonate species and the coadsorbed bidentate carbonate species and hydroxyls is only 0.04 eV on the (110) surface, but the difference reaches 0.97 eV on the (100) surface. The activation barrier for forming the bicarbonate species on the (100) surface, 0.42 eV, is also lower than that on the (110) surface (0.53 eV).     

Competitive Adsorption of Ferricyanide and Ferrocyanide on gamma-Al(2)O(3) Surface

In the past 3 decades, research has proven the significance of competitive adsorption in the equilibrium of pollutants between solid and liquid phases. However, studies on the competitive adsorption of complex ions are very limited in spite of its important role in transporting pollutants in the natural environment. The objective of this study is to derive the thermodynamic parameters of the competitive adsorption between ferricyanide and ferrocyanide from the modified Langmuir isotherm and the triple-layer model (TLM) to determine the location of adsorption. The effects of pH, temperature, and ion concentration on competitive adsorption onto gamma-Al(2)O(3) were investigated. The results demonstrate that ferrocyanide is more competitive than ferricyanide. By comparing the derived K(app) with K(int), we inferred that the adsorption of ferricyanide and ferrocyanide onto gamma-Al(2)O(3) was achieved through outer-sphere complexation. The negative DeltaH degrees indicated that the adsorption was exothermic. The positive entropy (Delta S degrees ) was caused by the replacement and release of a greater number of smaller surface ions by adsorbed ferricyanide and ferrocyanide ions of larger size. Copyright 2000 Academic Press.     

A novel catalyst for hydrazine decomposition: molybdenum carbide support on gamma-Al2O3

An alumina-supported Mo2C catalyst is found to be as active as a conventionally used Ir/gamma-Al2O3 catalyst for catalytic decomposition of hydrazine tested in a monopropellant thruster.     

Kinetic Adsorption of Cd onto Nanometer Al2O3/Carbon Fibre

Introduction There are many vast water areas where water con-tains higher contents of metals than the recommendedconcentrations with the rapid development of machinemanufacturing, metallurgical industry, organic chemi-cal industry, petrochemical industry, and mining in-dustry in recent years. Ingesting the water with metalconcentrations exceeding the limit exerts a harmfuleffect on human health.Removal of metals from aqueous media can beachieved by electrodialysis, chemical precipitation, ad-s…     

Mesostructured forms of gamma-Al(2)O(3)

gamma-Al2O3 is one of the most extensively utilized metal oxides in heterogeneous catalysis. Conventional forms of this oxide typically exhibit a surface area and pore volume less than 250 m2/g and 0.5 cm3/g, respectively. Previous efforts to prepare mesostructured forms of alumina resulted only in structurally unstable derivatives with amorphous framework walls. The present work reports mesostructured aluminas with walls made of gamma-Al2O3, denoted MSU-gamma. These materials are structurally stable and provide surface areas and pore volumes up to 370 m2/g and 1.5 cm3/g, respectively. The key to obtaining these structures is the formation of a mesostructured surfactant/boehmite precursor, denoted MSU-S/B, assembled through the hydrolysis of an aluminum cation, oligomer, or molecule in the presence of a nonionic surfactant. Mesostructured, gamma-aluminas offer the possibility of improving the catalytic efficiency of many heterogeneous catalytic processes, such as petroleum refining, petrochemical processing, and automobile exhaust control.     

Pb(II) sorption onto gamma-Al2O3 surfaces at the oxide-water interface: a novel approach using planar oxides

A novel technique for examining metal-ion interactions at the solid-water interface is introduced. Planar oxides, flat, thin coatings of uniform thickness created on a metal support, have been constructed as useful analogs for investigating metal-solid interactions under a variety of conditions. XPS and ToF/SIMS results from sorption studies at pH 6.0 show that the sorption behavior of Pb on each phase is similar with Pb binding preferentially to the bulk gamma-Al(2)O(3). This may be due to the presence of defect sites on the bulk oxides, the preferential exposure of a specific crystallographic plane in the planar oxides, or it may be an artifact of instrumental analysis. A second study examining Pb sorption to planar gamma-Al(2)O(3) under a series of increasingly complex conditions shows that our methods are able to successfully characterize sorption complexes formed in the presence of environmentally derived complexants. Results suggest that Pb is more strongly complexed by aqueous phase organic matter than sediment-bound organic material, indicating a possible control on Pb sorption in natural environments. Overall, the use of planar oxides combined with a powerful suite of spectroscopic tools provides a promising approach to better understanding metal ion sorption to natural sediment surfaces in aquatic environments.     

Aberration-corrected STEM imaging of Ag on gamma-Al2O3.

Ag on gamma-alumina is a promising catalyst for hydrocarbon selective catalytic reduction in lean-burn gasoline and diesel engines for transportation applications. Although much is known about the mechanism of NOx reduction and the various intermediates, little agreement exists on the nature of the active silver species. In the present work, aberration-corrected STEM has provided new information about the nature of Ag on alumina both as impregnated and following treatments at various temperatures with exposure to simulated exhaust gas. Ex situ techniques have provided new insights into the evolution of Ag on alumina following exposure to temperature and simulated exhaust gas.     

Characterization of Pd-Cu alloy nanoparticles on gamma-Al2O3-supported catalysts

Cu-Pd/Al2O3 bimetallic catalysts have been characterized by XRD, TEM, and EDX techniques. The surface structure has been investigated by FT-IR spectroscopy of low-temperature adsorbed CO in the reduced and in the oxidized state. Evidence has been provided of the formation of Cu-Pd alloy nanoparticles, both of the alpha-phase (disordered fcc) and of the beta-phase (ordered CsCl-type). IR spectra suggest that Cu likely decorates the edges while Pd mostly stays at the main faces. Part of copper disperses as Cu+ on the support even after reduction. The presence of copper seems to modify strongly the sate of oxidized Pd centers in oxidized high-Pd content materials. The redox chemistry of the system, where Pd is reduced more easily than Cu, appears to be very complex.     

Creating mixed Fe/Al coatings on planar gamma-Al2O3 surfaces

Insufficient understanding of the interactions of reactive phases (e.g., Fe and Al oxides) with minerals, other reactive phases and sorbing species has made predicting and modeling metal sorption on natural sediment surfaces difficult. This work develops a method to create mixed Fe/Al planar oxide surfaces by coating well-characterized planar gamma-Al2O3 with ferric iron. The objective is to closely control the Fe/Al ratio as well as the distribution of Fe on the planar surface. Effects of starting Fe(III) concentration, reaction time and number of coating sequences were examined using XPS and ToF-SIMS. No observable trend was seen in Fe/Al ratios by varying the starting Fe(III) concentration or reaction time. For both 4- and 14-day reactions, lower concentrations of Fe(III) produced oxide phases with a homogeneous distribution of Fe at the surface as detected by ToF-SIMS. ToF-SIMS Fe elemental maps of the oxide phases resulting from the highest Fe(III) concentration showed areas of localized Fe deposition. A sequential coating procedure allowed for a closer control of the concentration and spatial distribution of Fe(III) in the resulting oxide phase. This work provides methodology that can be used to create Fe/Al oxide phases whose Fe/Al content can be controlled for use in subsequent sorption studies to better understand the effects of mixed phase oxides on metal ion uptake.     

Water-induced morphology changes in BaO/gamma-Al2O3 NOx storage materials

Exposure of NO(2)-saturated BaO/gamma-Al(2)O(3) NO(x) storage materials to H(2)O vapour results in the conversion of surface nitrates to Ba(NO(3))(2) crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NO(x) storage/reduction properties of these materials.     

Anion specific adsorption on Fe2O3 and AlOOH nanoparticles in aqueous solutions: comparison with hematite and gamma-Al2O3

The specific adsorption of radiolabeled sulfate and phosphate ions from perchlorate supporting electrolyte onto nano-AlOOH and nano-Fe(2)O(3) powder has been investigated. The pH dependence of the adsorption of anions onto nanopowders was compared with that of the same ions onto gamma-Al(2)O(3) and hematite. It was demonstrated that the character of the pH dependence of the adsorption is very similar in the comparable cases. It was found, however, that in contrast to the behavior of gamma-Al(2)O(3), nano-AlOOH dissolves at a significant rate at low pH values (pH<2). Thus the study of the pH dependence of the anion adsorption encounters difficulties at these pH values. Disregarding this fact, it can be concluded that no special effects can be observed in the anion adsorption onto the nano-oxides studied.     

Easy replication of Pueraria Lobata toward hierarchically ordered porous gamma-Al2O3

Hierarchically ordered porous alumina was prepared via a facile immersion-fuming-calcination process using Pueraria lobata as template. The as-prepared alumina inherited nearly all morphological features of the template, as shown by SEM observations. It also contains abundant mesopores based on nitrogen adsorption-desorption measurements. The crystalline phase of the as-prepared alumina was ascertained to be gamma-alumina by analyzing its XRD pattern. Pt nanoparticles were in situ synthesized in the gamma-alumina matrix and annealed at different temperatures in N(2) atmosphere. TEM observations showed that Pt nanoparticles supported by the as-prepared alumina have significantly high thermal stability.     

聚丙烯腈活性炭纤维对硫化氢的常温吸附

聚丙烯腈活性炭纤维（PAN-ACF）对硫化氢（H2S）有比其他活性炭材料更强的吸附能力。H2S在PAN-ACF上的吸附是一个兼具物理吸附特征的化学吸附、催化转化过程。其化学吸附位主要位于微孔表面。吸附过程为：H2S分子首先被物理吸附进入微孔空间,而后在微孔表面的化学吸附位上进行包含电子转移的化学吸附、催化氧化,在炭表面产生相对稳定的化学结构。     

Reactivity of site-isolated metal clusters: propylidyne on gamma-Al2O3-supported Ir4.

To contrast the reactivity of supported metal clusters with that of extended metal surfaces, we investigated the reactions of tetrairidium clusters supported on porous gamma-Al2O3 (Ir4/gamma-Al2O3) with propene and with H2. Infrared, 13C NMR, and extended X-ray absorption fine-structure spectroscopy were used to characterize the ligands formed on the clusters. Propene adsorption onto Ir4/gamma-Al2O3 at 298 K gave stable, cluster-bound mu3-propylidyne. Propene adsorbed onto Ir4/gamma-Al2O3 at 138 K reacted at approximately 219 K to form a stable, highly dehydrogenated, cluster-bound hydrocarbon species approximated as CxHy (such as, for example, C3H2 or C2H). H2 reacted with Ir4/gamma-Al2O3 at 298 K, forming ligands (likely hydrides), which prevented subsequent reaction of the clusters with propene to form propylidyne. Propylidyne on Ir4 was stable in helium or H2 as the sample was heated to 523 K, whereupon it reacted with oxygen of the support to give CO. Propylidyne on Ir4 did not undergo isotopic exchange in the presence of D2 at 298 K. In contrast, the literature shows that propylidyne chemisorbed on extended metal surfaces is hydrogenated in the presence of H2 (or D2) and exchanges hydrogen with gaseous D2 at room temperature; in the absence of H2, it decomposes thermally to give hydrocarbon fragments at temperatures much less than 523 K. The striking difference in reactivities of propylidyne on clusters and propylidyne on extended metal surfaces implies the requirement of ensembles of more than the three metal surface atoms bonded to propylidyne in the surface reactions. The results highlight the unique reactivity of small site-isolated metal clusters.     

Mesostructured gamma-Al(2)O(3) with a lathlike framework morphology

A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike gamma-Al(2)O(3) nanoparticles. In the initial supramolecular assembly step of the pathway a mesostructured alumina with a wormhole framework morphology and amorphous pore walls is assembled through the hydrolysis of Al(13) oligocations and hydrated aluminum cations in the presence of a nonionic diblock or triblock poly(ethylene oxide) surfactant as the structure-directing porogen. The walls of the initial mesostructure are then transformed in a second hydrolysis step at a higher temperature to a surfactant-boehmite mesophase, denoted MSU-S/B, with a lathlike framework made of boehmite nanoparticles. A final thermal reaction step topochemically converts the intermediate boehmitic mesophase to a mesostructure with crystalline gamma-Al(2)O(3) pore walls, denoted MSU-gamma, with retention of the lathlike framework morphology. The boehmitic MSU-S/B intermediates formed from the chloride salts of aluminum incorporate chloride anions into the mesostructure. Chloride ion incorporation tends to disorder the nanoparticle assembly process, leading to a broadening of the slit-shaped framework pores in the final MSU-gamma phases and to the introduction of intra- and interparticle textural mesopores. However, the well-ordered MSU-gamma phases made from aluminum nitrate as the preferred aluminum reagent exhibit narrow framework pore size distributions and average pore sizes that are independent of the surfactant size and packing parameter, in accord with a lathlike framework assembled from nanoparticles of regular size and connectivity. The high surface areas ( approximately 300-350 m(2)/g) and pore volumes ( approximately 0.45-0.75 cm(3)/g) provided by these mesostructured forms of gamma-Al(2)O(3) should be useful in materials and catalytic applications where the availability of surface Lewis acid sites and the dispersion of supported metal centers govern reactivity.