Structure and base properties of calcined hydrotalcites

Five hydrotalcites with Mg/Al molar ratio range of 3-15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar ratio and, the calcination temperature. Al-27-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(AI)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that Al(t) may be mainly from the surface Al. Temperature-programmed desorption (TPD) of CO2 shows that the number of basic sites of Mg(Al)O samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)(3) reveal that there are two kinds of basic sites: weak basic OH- sites and strong basic O2- sites on the Mg(AI)O samples, the base strength depends on the Mg/Al molar ratio and calcination temperature.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.

Co-Cu-Al mixed oxides derived from hydrotalcite-like compound for NO reduction by CO

Various hydrotalcite based catalysts were prepared for catalytic removal of NO (NO reduction by CO). The general formula of hydrotalcite compounds (HTLc) was Co-Cu-Al-HTLc. Precalcination of these materials at 450 degrees C for NO reduction by CO, was necessary for catalytic activity. All catalysts except Co-A1 and Cu-Al have very good activity at lower temperature for NO reduction by CO. All samples were characterized by XRD and BET. The tentative reaction mechanism was also proposed.

Catalytic alcohols synthesis from CO and H2O on TiO2 catalysts calcined at various temperatures

The reaction performance for CO hydration on a TiO2 catalyst under different calcination temperatures was investigated. Under reaction conditions of T = 573 K, P = 0.5 MPa, CO flow rate of 30 ml min(-1), TOS = 12 h, and CO/H2O (g) = 3/2 (mol), the TiO2 catalyst with a futile content of 18% shows a maximum alcohols STY of 1.81 Mg m(-2) h(-1). In addition, the catalyst deactivation and regeneration were discussed.

Alrylation Over Layered Double Hydrotalcites Pillared by Heteropolyoxometalate Catalysts

Layered double hydroxides (LDHs) pillared with heteropolyoxo-metalate have been synthesized via both restructuring of hydrotalcite-like compounds and direct anion exchange under microwave field. LDHs and their derivatives are both found to be efficiency f

Growth of zeolite KSO1 on calcined kaolin microspheres

Zeolite KSO1 was successfully synthesized on calcined kaolin microspheres (ca. 60-80 mu m) in situ, and characterized by powder X-ray diffraction, scanning electronic microscopy and nuclear magnetic resonance spectroscopy.

Luminescence characteristics of Yb3+, La3+ codoped yttrium oxide nanopowders

Luminescence characteristics of Yb3+, La3+ codoped yttrium oxide nanopowders were investigated. The grain size and the crystallinity of (Yb0.05Y0.90La0.05)(2)O-3 nanopowders increase with the increase of calcination temperature. The average grain size of the nanopowders calcined at 1100 degrees C is 66 nm and its cooperative up-conversion luminescence centered at 498 nm was detected due to nanometer size effect and perfect crystallinity. However, the cooperative up-conversion luminescence of (Yb0.05Y0.90La0.05)(2)O-3 transparent ceramics was not detected. (c) 2008 Elsevier B.V. All rights reserved.

Transparent and Light-Emitting Epoxy Super-Nanocomposites Containing ZnO-QDs/SiO2 Nanocomposite Particles as Encapsulating Materials for Solid-State Lighting

In this article, the ZnO quantum dots-SiO2 (Z-S) nanocomposite particles were first synthesized. Transparent Z-S/epoxy super-nanocomposites were then prepared by introducing calcined Z-S nanocomposite particles with a proper ratio of ZnO to SiO2 into a transparent epoxy matrix in terms of the filler-matrix refractive index matching principle. It was shown that the epoxy super-nanocomposites displayed intense luminescence with broad emission spectra. Moreover, the epoxy super-nanocomposites showed the interesting afterglow phenomenon with a long phosphorescence lifetime that was not observed for ZnO-QDs/epoxy nanocomposites. Finally, the transparent and light-emitting Z-S/epoxy super-nanocomposites were successfully employed as encapsulating materials for synthesis of highly bright LED lamps.

Al2O3 : Cr3+ nanotubes synthesized via homogenization precipitation followed by heat treatment

Cr3+-doped NH4Al(OH)(2)CO3 nanotubes, templated by surfactant assemblies, were successfully synthesized via the homogenization precipitation method, and various crystallographic phase Al2O3:Cr3+ nanotubes were also obtained by postannealing at different temperatures. The characteristic R-1, R-2 doublet line transitions of ruby can be observed in the high crystalline alpha-Al2O3 nanotubes calcined at temperatures higher than 1200 degrees C. The results also indicate that the formation mechanism of the tubular nanostructures should result from the self-rolling action of layered compound NH4Al(OH)(2)CO3 under the assistance of the surfactant soft-template. The convenient synthetic procedure, excellent reproducibility, clean reactions, high yield, and fine quality of products in this work make the present route attractive and significant. Aluminum oxide nanotubes with high specific surface area could be used as fabricating nanosized optical devices doped with different elements and stable catalyst supports of metal clusters.

Direct synthesis of Al-SBA-15 mesoporous materials via hydrolysis-controlled approach

Aluminum-substituted mesoporous SBA-15 (Al-SBA-15) materials were directly synthesized by a hydrolysis-controlled approach in which the hydrolysis of the silicon precursor (tetraethyl orthosilicate, TEOS) is accelerated by fluoride or by using tetramethyl orthosilicate (TMOS) as silicon precursor rather than TEOS. These materials were characterized by powder X-ray diffraction (XRD), N-2 sorption isotherms, TEM, Al-27 MAS NMR, IR spectra of pyridine adsorption, and NH3-TPD. It is found that the matched hydrolysis and condensation rates of silicon and aluminum precursors are important factors to achieve highly ordered mesoporous materials. Al-27 MAS NMR spectra of Al-SBA-15 show that all aluminum species were incorporated into the silica framework for the samples prepared with the addition of fluoride. A two-step approach (sol-gel reaction at low pH followed by crystallization at high pH) was also employed for the synthesis of Al-SBA-15. Studies show that the two-step approach could efficiently avoid the leaching of aluminum from the framework of the material. The calcined Al-SBA-15 materials show highly ordered hexagonal mesostructure and have both Bronsted and Lewis acid sites with medium acidity.

A strategy to prepare ultrafine dispersed Fe2O3 nanoparticles

In this article, a novel strategy was applied to prepare dispersed ultrafine alpha-Fe2O3 nanoparticles. The initial Fe(OH)(3) nanoparticles were synthesized by the reaction of NaOH and FeCl3 in alcohol. With the new-formed nanoparticles as nuclei, NaCl crystallized and encapsulated the particles into solid cages. As a result, the nanoparticles were prevented from aggregating and growing. The composite of Fe(OH)(3) and NaCl was calcined and then washed by water to obtain the pure alpha-Fe2O3 nanoparticles.