Octahedral Aluminum Research Articles

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina–fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600 °C. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500 °C for 1 h. Thus, the rupture strength of alumina–26.52 wt% Fap–1.4 wt% TiO 2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO 2 , the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina–Fap–TiO 2 composites shows the formation of aluminium titanate (Al 2 O 3 –TiO 2 : Al 2 TiO 5 ). The 27 Al magic angle scanning nuclear magnetic resonance analysis of Al 2 O 3 –Fap–TiO 2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.

Influence of the nitric acid treatment on Al removal, framework composition and acidity of BEA zeolite investigated by XRD, FTIR and NMR

Two different procedures were used to prepare dealuminated BEA zeolite. The first procedure realized in two steps consisted of first calcination of original tetraethylammonium (TEA) BEA(17) zeolite in air at 823K for 15h to remove organic template and then treatment of as resulted organic-free HAlBEA(17) zeolite with concentrated nitric acid solution for different times to remove part or all Al atoms. Two periods was distinguished in the removal of Al atoms from HAlBEA(17) framework during the first procedure. During initial period (up to 0.08h), the dealumination was very fast and 94% of Al was removed. This period corresponded to the easy removal of extra framework octahedral and framework tetrahedral aluminum from T3-T9 sites. In the second period (from 0.08 to 4h), the dealumination was much slower. It corresponded to a much more difficult removal of framework tetrahedral aluminum from T1 and T2 sites. The second procedure realized in one step consisted of direct treatment of original TEABEA zeolite with concentrated nitric acid solution to remove simultaneously organic template and Al atoms. To obtain partly or totally dealuminated BEA zeolite the treatment time was 0.08 and 4h respectively. The influence of the nitric acid treatment on Al removal, framework composition and acidity of BEA zeolite were investigated by XRD, FTIR and NMR. 2D 27Al 3Q MAS NMR allowed distinguishing two kinds of framework tetrahedral Al atoms (AlTd(2a) and AlTd(2b)) in BEA zeolite which relative amounts depended on the Si/Al ratio. The Brønsted and Lewis acidic centers were evidenced in dealuminated BEA zeolites by FTIR spectra of adsorbed pyridine and CO use as probe molecules. Their relative amounts depended on the degree of dealumination and procedure used for removal Al atoms.

Fluorinated Hydrotalcites: The Addition of Highly Electronegative Species in Layered Double Hydroxides To Tune Basicity

Hydrotalcite-like compounds were synthesized by coprecipitation using a constant-pH method. Aluminum was introduced in the form of an octahedral aluminum fluorine complex during the synthesis. Controlling the pH during the synthesis ensured that aluminum fluorine did not decompose to tetrahedral species but remained in the octahedral (AlF(6))(3-) form to be incorporated into brucite-like sheets. The physicochemical, thermal, and spectroscopic characterizations showed significant modifications by fluorine introduction regarding structural, textural, and adsorption properties. The memory effect of fluorinated hydrotalcites differed from the memory effect commonly observed in fluorine-free hydrotalcites. Nitromethane adsorption showed that the basicity of hydrotalcite was greatly modified by the fluorine loading.

Structural incorporation of titanium and/or aluminum in layered silicate magadiite through direct syntheses

Synthesized inorganic layered magadiite containing structurally incorporated titanium and aluminum was obtained through hydrothermal procedures. The effects associated with reaction time and amount of metal used in the crystallization process yielded mostly pure and crystalline samples with 1.0% of aluminum after 36 h at 423 K. Amounts up to 4.0 and 2.0% for aluminum and titanium were successfully incorporated in the magadiite structure without co-crystallization of other phases. A higher amount of metal source or longer crystallization times led to formation of crystobalite and trydimite phases, detected by X-ray diffraction (XRD) and scanning electron microscopies. Metal incorporation slightly improved the thermal resistance of the precursor layered magadiite. Replacement of both atoms in the silicon network was examined by spectroscopy analysis. The changes in tetrahedral-oxygen-tetrahedral structural shape vibrations caused the appearance of the Ti–O–Si band at 960 cm−1. Nuclear magnetic resonance in the solid state demonstrated tandem octahedral and tetrahedral aluminum sites. Another structural feature related to titanium incorporation was observed through diffuse reflectance with UV–Vis and X-ray photoelectron spectroscopies, which distinguish crystalline and amorphous TiO2 and titanium incorporated into the silica network. Metal quantification by energy dispersive spectroscopy and X-ray fluorescence (XRF) was also followed with multivariate analysis, including principal component analysis (PCA) and partial least squares (PLS). The PCA methodology procedure clearly gives information to separate sample groups, in agreement with XRD results, which becomes a valuable feature obtained for the first time for these kinds of materials.

Novel Amphibole Geo-barometer with Application to Mafic Xenoliths

Amphibole crystallization from hydrous high-magnesium andesite (Shiveluch volcano, Kamchatka) melt has been studied experimentally at pressures 2, 3, 5 kbar. Slightly subliquidus temperatures have been selected for amphibole crystallization. Amphiboles with close to the equilibrium composition have been obtained at low undercoolings in short 4 hours experiments. We select octahedral aluminium content and sum of high charged cations (Ti 4+ , Fe 3+ ) all evaluated with the 13eCNK method as master parameters reflecting pressure of amphibole formation. Asymptotic maximum of Al VI content at the sum Ti+Fe 3+ =0 as a function of pressure was calculated following negative linear correlation trend for each run of the original and published experimental data sets. The derived novel Al VI in amphibole barometer is calibrated in the pressure range of 2-12 kbar for andesitic and basaltic magmas. Reliability and validity of the new geobarometer were tested on the amphibolized ultramafic xenoliths from the Shiveluch Volcano (Kamchatka) and Dish Hill (California). In both cases our estimates appear to be equal within the uncertainty of the method to the predictions done by two-pyroxene geo-thermo-barometer (Putirka, 2008).

U(VI) sorption on montmorillonite in the absence and presence of carbonate: A macroscopic and microscopic study

The mechanism of U(VI) sorption on montmorillonite (Na-SWy-1) in the absence and presence of carbonate was investigated through a combination of different approaches: macroscopic sorption experiments, surface complexation modelling using the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange sorption model and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. U(VI) sorption measurements were performed in the absence of carbonate at fixed ionic strength (0.1M NaClO4) as a function of pH at U(VI) trace concentration (∼9×10−8M) and as a function of U(VI) concentration (∼10−7–10−4M) at a fixed pH (5, 6.8 and 8). In the presence of carbonate, experiments were carried out in equilibrium with atmospheric pCO2 and in 1, 3 and 5mM NaHCO3. The pH dependent sorption measurements at trace concentration in the absence of carbonate were modelled by considering the formation of the following surface species, SSOUO2+, SSOUO2OH0, SSOUO2(OH)2- and SSOUO2(OH)32- on the strong sites. From the isotherms the formation of SW1OUO2+ and SW1OUO2OH0 on the weak sites was inferred. Two additional surface complexes on the strong sites, SSOUO2CO3- and SSOUO2(CO3)23- and one surface complex on the weak sites, SW1OUO2CO3-, were necessary to reproduce the sorption data obtained in the presence of carbonate. The EXAFS measurements did not allow to verify the formation of ternary uranyl-carbonate complexes on the montmorillonite surface. However, the obtained fit results, i.e. splitting of the equatorial oxygen shell, one Si/Al shell at ∼3.09Å and one Si/Al at ∼3.29Å or one Fe shell at ∼3.42Å, clearly indicate that under the given experimental conditions (pH, U(VI) loading) U(VI) forms inner-sphere surface complexes on montmorillonite edge sites via binding to aluminum octahedra and/or silicon tetrahedra.

Magnetic structure of almandine

The magnetic structure of almandine has been investigated by electronic structure calculations in the local spin density approximation in order to arrive at a more detailed understanding of the magnetic structure and the exchange pathways. The calculations are based on experimentally determined geometrical data of the crystal structure at 100 K. The calculated quadrupole splittings, spin-allowed d–d transitions and magnetic moment for iron atoms are in reasonable agreement with the respective experimental values obtained by Mossbauer and absorption spectroscopy, and magnetization measurements demonstrating the reliability of the calculations. The spin structure is derived from the calculated coupling constants for the possible exchange pathways. The competing superexchange pathways exist via oxygen bridges between directly neighboured iron ions and via edges of silicon tetrahedra and aluminium octahedra connecting more distant iron dodecahedra. Careful consideration revealed that almandine structure contains two identical interpenetrative sublattices of Fe dodecahedra connected via Al octahedra and Si tetrahedra. The calculations provide the information about ferromagnetic interaction between the iron spins within each sublattice, whereas the coupling between two magnetic sublattices is weakly antiferromagnetic via Al octahedra and Si tetrahedra. This antiferromagnetic interaction of two identical magnetic sublattices is in good agreement with the experiments and explains the Mossbauer spectra of almandine below the Neel temperature. Since almandine belongs to most abundant crystallized silicates that are main constituents of the earth and main components of cosmic dust, these results have scientific importance of studying the universe.

Effects of hydrothermal aging on NH3-SCR reaction over Cu/zeolites

The effects of hydrothermal treatment on model Cu/zeolite catalysts were investigated to better understand the nature of Cu species for the selective catalytic reduction of NOx by NH3. After hydrothermal aging at 800°C for 16h, the NOx reduction performance of Cu-ZSM-5 and Cu-beta was significantly reduced at low temperatures, while that of Cu-SSZ-13 was not affected. When the zeolite framework aluminum species were probed using solid state 27Al MASNMR, significant reduction in the intensities of the tetrahedral aluminum peak intensity was observed for Cu-ZSM-5 and Cu-beta, although no increase in the intensities of the octahedral aluminum peak was detected. When the redox behavior of Cu species was examined using H2-TPR, it was found that Cu2+ could be reduced to Cu+ and to Cu0 for Cu-ZSM-5 and Cu-beta catalysts, while Cu2+ could be reduced only to Cu+ in Cu-SSZ-13. After hydrothermal aging, CuO and Cu-aluminate species were found to form in Cu-ZSM-5 and Cu-beta, while little changes were observed for Cu-SSZ-13.

High Temperature Structural Modifications of Intercalated Montmorillonite Clay Mineral with OH-Al Polymers

Two montmorillonitic clays were put into contact with a solution containing inorganic OH-Al polymers and subsequently washed and dried. The obtained solid (i.e.the clays with the OH -Al species in the montmorillonite interlayer) which was called the precursor, was subjected to a thermal treatment up to 1000 ¡ C using DTA-TG for analysis at low temperature. Additionally, the structural changes of the precursor by heating at 1030, 1100 and 1200 ¡ C for 2hours and that of the natural clays were examined. The crystallinity and formation of new phases was followed by x-ray diffraction analysis. Mullite and cordierite were originated depending on the different contents of aluminium and magnesium in the structure of natural montmorillonite, respectively, accompanied with other phases. The intercalated OH-Al species in both clays favored the increase in the mullite content in the final products. However, the transformation to this phase was directly related to the octahedral aluminium of the natural clay and thus mullite was found to be the dominant phase from montmorillomite containing higher octahedral Al.

The structural influence of aluminium ions on emission characteristics of Sm 3+ ions in lead aluminium silicate glass system

Optical absorption and photoluminescence characteristics of Sm 3+ ions in lead silicate glasses mixed with different concentrations of Al 2O 3 (5–10 mol%) have been investigated. From these studies, the radiative properties viz., spontaneous emission probability A, the total emission probability, the radiative lifetime τ R, the fluorescent branching ratio β of emission transition of 4G 5/2 → 6H 7/2 along with other transitions for Sm 3+ have been evaluated and found to be the highest for the glass mixed with 8.0 mol% of Al 2O 3.The IR spectral studies have indicated that Al 3+ ions do participate in the glass network with AlO 4 and AlO 6 structural units and further revealed that the concentration of octahedral aluminium ions induce bonding defects in the glass network. Such bonding defects are assumed to be responsible for low phonon losses in these glasses and lead to higher values of radiative parameters for the glass mixed with 8.0 mol% of Al 2O 3.

Monitoring the Activation Process of the Giant Pore MIL-100(Al) by Solid State NMR

The structure of mesoporous MIL-100 consists of Al3 aluminum octahedra trinuclear units sharing a common oxo vertex μ3-O, interconnected through 1,3,5-benzenetricaboxylate (btc) ligands. Each Al is bonded to four framework carboxylate functions, and the corresponding octahedra exhibit therefore a terminal position occupied either by a water molecule or by a hydroxide group. The ability of a reversible removal of coordinated water upon dehydration/rehydration process has been investigated using solid state NMR techniques. Double resonance techniques such as 1H{27Al} TRAPDOR (transfer population in double resonance) and 27Al{1H} HETCOR (heteronucleus correlation) were used to probe the proximity between species containing protons and the inorganic framework. On the other hand, 1H–1H correlation experiments using the DQ-BABA and RFDR sequences were employed to investigate the interaction between the different kinds of protonic species, including those of the organic framework. The compound shows a remarkable...

Covalent Grafting to μ-Hydroxy-Capped Surfaces? A Kaolinite Case Study

All μ-hydroxyl groups are frequently encountered capping groups found on the external surfaces of various minerals that are often used as fillers in composite materials. Covalent grafting to this functional group would therefore offer a versatile and attractive route to surface modification. The octahedral layer of kaolinite is composed of μ-bridged aluminol groups. In particular, intercalation compounds of kaolinite, where all basal planes are exposed and may be modified, are ideally suited to study the feasibility of such covalent graftings. The huge (internal) specific surface area greatly improves the sensitivity of the analytics and renders kaolinite an ideal model compound. Herein we analyze the mode of bonding of ethylene glycol (EG), intercalated into kaolinite (EG kaolinite), by solid-state NMR techniques. 27Al MQMAS allows for distinction between intercalated and grafted EG molecules because the chemical surroundings of octahedrally coordinated aluminum nuclei in the layer are significantly changed by the formation of a covalent bond. Moreover, the temperature-dependent dynamics of the EG molecules in the interlamellar space are examined by wide-line solid-state 1H NMR measurements. The EG molecules perform a circular motion around the covalently bonded hydroxyl group in the interlamellar space. Analysis of the 13C–27Al REAPDOR measurement in conjunction with the EG dynamics allows for determination of the 13C···27Al distance between octahedral aluminum and the bonded carbon atom of EG. This distance is 3.1 Å. A thorough description of the bonding mode of the EG molecules is provided and proves beyond any doubt the covalent grafting. This suggests that the reactivity of μ-hydroxyl groups, in general, is sufficient to realize a covalent surface modification of a wide range of minerals.

Aluminum Incorporation in TiO2 Rutile at High Pressure: An XRD and High-Resolution 27Al NMR Study

Aluminum incorporation into rutile (TiO2) at high pressure and high temperature has been studied by XRD as well as high-resolution 27Al MAS NMR and MQ MAS NMR. High pressure enhances the Al solubility into TiO2 rutile, which is able to incorporate up to at least 5 wt % Al2O3 at 5.5 GPa. Up to four aluminum environments in octahedral coordination in rutile have been observed. The main mechanism of solubility at low pressure is the substitution of Ti4+ by Al3+ on normal octahedral sites, but aluminum also occupies octahedral interstices of rutile, especially at higher pressures. The assignation of the NMR signals corresponding to interstitial Al and subtitutional Al associated with an interstitial Al in the rutile structure has been carried out from the combination of both XRD and NMR data and the relative higher importance of both environments at high pressure. The increase of the population of interstitial octahedral aluminum with increasing pressure gives rise to the reduction of symmetry in rutile from tetragonal to orthorhombic.

Coordination-driven self-assembly of M3L2 trigonal cages from preorganized metalloligands incorporating octahedral metal centers and fluorescent detection of nitroaromatics.

The design and preparation of novel M(3)L(2) trigonal cages via the coordination-driven self-assembly of preorganized metalloligands containing octahedral aluminum(III), gallium(III), or ruthenium(II) centers is described. When tritopic or dinuclear linear metalloligands and appropriate complementary subunits are employed, M(3)L(2) trigonal-bipyramidal and trigonal-prismatic cages are self-assembled under mild conditions. These three-dimensional cages were characterized with multinuclear NMR spectroscopy ((1)H and (31)P) and high-resolution electrospray ionization mass spectrometry. The structure of one such trigonal-prismatic cage, self-assembled from an arene ruthenium metalloligand, was confirmed via single-crystal X-ray crystallography. The fluorescent nature of these prisms, due to the presence of their electron-rich ethynyl functionalities, prompted photophysical studies, which revealed that electron-deficient nitroaromatics are effective quenchers of the cages' emission. Excited-state charge transfer from the prisms to the nitroaromatic substrates can be used as the basis for the development of selective and discriminatory turn-off fluorescent sensors for nitroaromatics.

Highly ordered, thermally/hydrothermally stable cubic Ia3d aluminosilica monoliths with low silica in frameworks

High order aluminosilica monoliths (Al/HOM-5) with cubic Ia3d structures were fabricated with low silica content (Si/Al = 1) by means of a simple, reproducible, and one-pot synthesis strategy. A realistic control over the cubic Ia3d geometry of aluminosilica monoliths was achieved by using microemulsion phases of copolymer P123 (EO 20PO 70EO 20) as soft templates. The textural and geometrical pore structures and acidic properties of Al/HOM-5 were characterized by means of various tools of XRD, N 2 isotherms, HRTEM, FTD, FESEM, 27Al and 29Si MAS NMR, EDX, and NH 3-TPD. The incorporated amounts of Al species in Al/HOM-5 monoliths play a key determinant in the formation of the coordination state of the aluminum species in four (Al IV, AlO 4)-, five (Al V, AlO 4)-, and six (Al VI, AlO 6)-coordinate environments. Results show evidence of the formation of aluminosilicas with disordered distribution of Si and Al sites in the frameworks. In addition, the increase of the aluminum contents enhanced the distortion in the pore uniformity of Al/HOM-5 monoliths. The large amount of acid sites was revealed with the high aluminum contents into the pore framework walls. With high-temperature treatments (⩾1073 K), the γ-Al 2O 3 phase with face-centered-cubic Fd3m symmetry can be formed in the monolithic aluminosilica matrices. This finding might indicate that the dealumination effect at high thermal treatment would be expected to generate many defect sites existing in the Al/HOM-5 frameworks. Accordingly, a large mass transport of aluminum from tetrahedral aluminum (framework) to octahedral aluminum (extra framework) was occurred, leading to form a separate aluminum species into the crystalline alumina matrices. Moreover, cubic Ia3d aluminosilica structures exhibit outstanding steam stability even with high Al content (Si/Al = 1). However, the mesostructured integrity of Al/HOM-5 can be retained under 100% steam treatments with N 2 flow for 8 h at 1073 K, permitting their desirability in various applications such as catalysis, adsorption, and sensing technologies.

Hydrogen bonds and local symmetry in the crystal structure of gibbsite

First-principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the (27)Al MAS NMR resonances in gibbsite. The (27)Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished (27)Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al-I site characterized by a C(Q) = 4.6 MHz is surrounded by OH-groups participating in four intralayer and two interlayer hydrogen bonds, while the Al-II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH-bonds are aligned toward the interlayer gallery. In high-resolution solid-state (1)H CRAMPS (combination of rotation and multiple-pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite-like layer-intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides.

ChemInform Abstract: Investigation of Dealuminated Mordenites by X-Ray Photoelectron Spectroscopy.

Mg K-alpha X-ray photoelectron spectroscopy (XPS) was used to establish the relative concentration and the chemical state of aluminum at the surface of dealuminated mordenites. A method for the binding energy calibration is proposed. Modified Auger parameters of Al have been determined for different zeolites and clay minerals as well as for dealuminated mordenites. The data are compared with those available in the literature. Ranges of values for modified Auger parameter of octahedral and tetrahedral aluminum are reported. The results obtained on highly dealuminated mordenites are consistent with the presence of surface tricoordinated Al.

Hexa-coordinated aluminum and gallium cations derived from indazole

trans-Dichloro- tetrakis-(indazole)aluminum(III) tetrachloroaluminate(III) 1 and trans-dichloro- tetrakis-(indazole)gallium(III) tetrachlorogallate(III) 3 were obtained by the asymmetric cleavage of the chloride-bridged dimers [AlCl 3] 2 and [GaCl 3] 2 with two moles of indazole and characterized by NMR, X-ray diffraction, EA and IR. The synthesis of 3 [1] was improved (yield 86%) using methylene chloride at room temperature. The addition of THF to a solution of 1/CH 2Cl 2 afforded in good yield complex 2 {[AlCl 2(IndH) 4] +[AlCl 4] −·4THF}. The crystal structures of these complexes are monoclinic in the space groups P2(1)/ n ( 1), C2/ c ( 2) and P2(1)/ n ( 3). The unit cells of 1– 3 contain ion pairs [ECl 2(IndH) 4] + [ECl 4] − (E = Al and Ga) with multiple hydrogen interactions (Cl⋯H 2.434–2.925 Å, O⋯H 1.984–2.665 Å, C⋯H 2.769–2.888 Å). The [ECl 2(IndH) 4] + cations show hexa-coordinated octahedral aluminum and gallium atoms with two chlorine atoms in anti positions and four coplanar nitrogen atoms from the indazole ligands. The [ECl 4] − anions have a tetrahedral coordination geometry around the central atom. In the lattice, the presence of THF molecules simplifies the weak interactions network in 2, so one AlCl 4 - anion interacts with two [MCl 2(Ind-H) 4] + cations and two THF molecules through Cl⋯H intermolecular interactions (2.855–2.922 Å) and one [MCl 2(Ind-H) 4] + cation interacts with two cations through ClL 4MCl⋯H interactions (2.922 Å). Whereas in 1 and 3, six AlCl 4 - anions interact through Cl⋯H intermolecular interactions (2.795–2.925 Å) with one [MCl 2(Ind-H) 4] + cation and this latter interacts with other three [MCl 2(Ind-H) 4] + cations through C⋯H interactions (2.769–2.888 Å). Additionally, every chlorine atom in the [MCl 2(Ind-H) 4] + cationic moieties is bounded by NCH⋯ClM or NH⋯ClM intramolecular-tetrafurcated hydrogen bonds (2.434–2.907 Å).

Step-wise dealumination of natural clinoptilolite: Structural and physicochemical characterization

The step-wise dealumination of a natural clinoptilolite has been achieved through a new milder treatment, comprising cycles of aqueous solutions of hydrochloric acid with washing steps. The course of the dealumination was monitored by XRD, FTIR, TGA, UV–vis-DRS and NMR. The XRD patterns show a contraction of cell volume during progressive dealumination steps and a decrease in crystallinity after the third dealumination cycle. The framework and OH vibrations in FTIR spectra show progressive extraction of aluminum atoms from zeolite framework and consequently the formation of silanol nests. 27Al MAS NMR indicates that low levels of octahedral aluminum species are created during the treatments.

Surface alumina species on modified titanium dioxide: A solid-state 27Al MAS and 3QMAS NMR investigation of catalyst supports

27Al MAS and 3QMAS NMR have been used to study Al 2O 3/TiO 2 catalyst supports synthesized via excess-solution impregnation and surface sol–gel methods. Temperature and alumina loading level strongly affect chemical states of aluminum oxide species observed. Surface cations, Al ( H 2 O ) 6 3 + , a surface alumina monolayer, and disordered transitional aluminas (multilayers) and α-alumina, coexist on the TiO 2 surface. Chemical shift and quadrupole coupling constants are reported for the major species identified in 3QMAS experiments. Gold particle catalysts prepared from supports calcined at 500 °C have optimum catalytic activity in CO oxidation, and smallest gold particle size for supports, which show maximum monolayer type octahedral alumina on the titania surface.