Characterization and Preparation of Ce-Zr-O Solid Solution

Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffraction, Raman and temperature programmed reduction. The phase composition and the reduction properties of Ce Zr O depend on the preparation method. A cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained by using the sol gel method. The Ce Zr O solid solution prepared by using decomposition or coprecipiation was composed of cubic Ce 0.8 Zr 0.2 O 2 and tetragonal Ce 0.2 Zr 0.8 O 2 solid solution. The Ce Zr O solid solution prepared with different methods shows the different reduction properties owing to different phase composition. Results of differential thermal analysis and XRD show that Ce 0.5 Zr 0.5 O 2 solid solution is formed during the decomposition or combustion of the gel.

Redox behavior of gold supported on ceria and ceria-zirconia based catalysts

A series of gold-based catalysts were prepared by deposition precipitation or incipient wetness impregnation on CexZ1-xO2 solid solutions （0.28≤x≤1.00）. The morphological and structural characterization of these catalysts were carried out with X-ray diffraction, trans- mission electron microscopy （TEM） analysis and physical adsorption technique, and their redox properties were studied by temperature programmed reduction using both H2 and CO as probe molecules. Two cycles of oxidation/reduction were carried out in order to evaluate the effects of redox aging and gold sintering on the oxygen exchange capability. As observed with other noble metals, gold enhanced and promoted the ceria reduction at lower temperatures. Reduction by CO was shown to be dependent on the fine dispersion of gold and to be nega- tively affected by the ageing process more than reduction with hydrogen. This might have implications in reactions like water gas shift and CO-PROX which involve CO as a main reactant.

Effect of cobalt loading on reducibility, dispersion and crystallite size of Co/Al_2O_3 Fischer-Tropsch catalyst

Co/Al2O3 Fischer-Tropsch synthesis catalysts with different cobalt loadings were prepared using incipient wetness impregnation method. The effects of cobalt loading on the properties of catalysts were studied by means of X-ray diffraction （XRD）, temperature programmed reduction （TPR）, hydrogen temperature programmed desorption （H2-TPD） and O2 titration. Co-support compound formation can be detected in catalyst system by XRD. For the Co/Al2O3 catalysts with low cobalt loading, CoAl2O4 phase appears visibly. Two different reduction regions can be presented for Co/Al2O3 catalysts, which belong to Co3O4 crystallites （reduction at 320 ℃） and cobalt oxide-alumina interaction species （reduction at above 400 ℃）. Increasing Co loading results in the increase of Co3O4 crystallite size. The reduced Co/Al2O3 catalysts have two adsorption sites, and cobalt loading greatly influences the adsorption behavior. With the increase of cobalt loading, the amount of low temperature adsorption is increased, the amount of high temperature adsorption is decreased, and the percentage reduction and cobalt crystallite size are increased.

Correlation between Iron Reducibility in Natural and Iron-Modified Clays and Its Adsorptive Capability for Arsenic Removal

The study reports aspects that allowed to correlate structural and redox properties of iron species deposited on clay minerals with the capacity of geomaterials for arsenic removal. Natural ferruginous clays as well as an iron-poor clay chemically modified with Fe(III) salt (ferrihydrite species) were investigated as adsorbents of the arsenate(V) in water. The study, carried out from minerals from abundant Argentinean deposits, was conducted with the aid of different techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM-EDS), Raman Spectroscopy, ICP-AES (Inductively Coupled Plasma) chemical analysis and Temperature Programmed Reduction (TPR). This last technique allowed to detect availability of iron species in oxidic environment with different structural complexity and to determine active sites, accessible for arsenate(V) adsorption. The effect was observed through temperature dependence of the first Fe(III) reduction step (below 570°C) of iron-oxide species. The sequence of reducibility: ferrihydrite > hydrous oxide (goethite) > anhydrous oxide (hematite) > structural iron in clay was in agreement with the availability of iron active sites for the reducing process as well as for the arsenate adsorption. The important role of very high iron content in original samples was also observed. The chemical activation of iron-poor clay by a simple and feasible modification with Fe(III) solutions promoted the deposition of the ferrihydrite active phase with an increase of 2.81% (expressed as Fe2O3) respect to the original content of 1.07%, constituting an accessible and eco-friendly technological alternative to solve the environmental problem of water containing arsenic.

N2O Decomposition Catalyzed by K＋-doped Bi0.02Co

K＋-doped Bi0.02Co was investigated as catalyst for N2O decomposition. It was found that the catalytic performance of the Bi0.02Co catalyst, which was prepared by coprecipitation method, can be effectively modified by potassium cations via impregnation. The optimized K0.01Bi0.02Co catalyst exhibited much higher activity compared with Bi0.02Co and K0.01Co for the reaction in feed gas 0.2% N2O/Ar, irrespective of the presence or absence of impurity gas（volume fraction） 5%02, 2%H20, 0.12%NO and 10%CO2. Characterization of the catalysts with H2 temperature programmed reduction（H2-TPR） and O2 temperature programmed desorption（O2-TPD） indicate that the Co--O bond in Bi0.02Co was weakened by the K＋ doping, and hence the K0.01Bi0.02Co catalyst has much higher turnover frequency（TOF） than CO3O4 spinel and Bi0.02Co for the reaction.