- [Show abstract] [Hide abstract] ABSTRACT: Density functional theory calculations of the relative stabilities of the ortho, meta, and para MClY(XC4H4)(PH3)2 heterometallabenzenes (M = Rh, Ir; X = N, P; Y = Cl and M = Ru, Os; X = N, P; Y = CO) have been carried out. The ortho isomer is the most stable for X = P, irrespective of the metal M. For X = N and M = Ir, Rh the meta is the lowest-lying isomer, whereas for M = Ru, Os the ortho and meta isomers are almost degenerate. The electronic structure and chemical bonding have been investigated with energy decomposition analyses of the interaction energy between various fragments, to discuss the origin of the differences observed. The values of the multicenter index of aromaticity and nucleus-independent chemical shifts indicate that the heterometallabenzenes studied should be classified as aromatic or slightly aromatic.
- [Show abstract] [Hide abstract] ABSTRACT: A central composite rotatable design and response surface methodology were used to optimize the experimental variables of the electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) degradations of 2.5L of sulfanilic acid solutions in 0.05M Na(2)SO(4). Electrolyses were performed with a pre-pilot flow plant containing a Pt/air diffusion reactor generating H(2)O(2). In SPEF, it was coupled with a solar photoreactor under an UV irradiation intensity of ca. 31Wm(-2). Optimum variables of 100mAcm(-2), 0.5mM Fe(2+) and pH 4.0 were determined after 240min of EF and 120min of SPEF. Under these conditions, EF gave 47% of mineralization, whereas SPEF was much more powerful yielding 76% mineralization with 275kWh kg(-1) total organic carbon (TOC) energy consumption and 52% current efficiency. Sulfanilic acid decayed at similar rate in both treatments following a pseudo-first-order kinetics. The final solution treated by EF contained a stable mixture of tartaric, acetic, oxalic and oxamic acids, which form Fe(III) complexes that are not attacked by hydroxyl radicals formed from H(2)O(2) and added Fe(2+). The quick photolysis of these complexes by UV light of sunlight explains the higher oxidation power of SPEF. NH(4)(+) was the main inorganic nitrogen ion released in both processes.
- [Show abstract] [Hide abstract] ABSTRACT: Two alumina-supported Ce/Pr mixed oxides, with different alumina promoters, La and Si, have been investigated in this paper. A gradual decrease of the Oxygen Storage Capacity (OSC) was observed after reducing the samples at progressively higher temperatures. However, depending on the nature of the alumina promoter, the temperature at which the loss of OSC started to be evident changed, being higher in the La-doped sample. A structural characterization study by X-ray diffraction (XRD) of the samples submitted to different reduction and reoxidation treatments in a range of temperatures was performed. From this study a correlation between the nature of the observed phases, the alumina promoter, and the deactivation behaviour could be stated. FTIR study is of particular interest because the observed correlation between the reduction degree and the position and intensity of the FTIR band is altered when deactivation phenomena appear.
- [Show abstract] [Hide abstract] ABSTRACT: Export Date: 6 February 2013, Source: Scopus, CODEN: CATTE, doi: 10.1016/j.cattod.2011.09.039, Language of Original Document: English, Correspondence Address: Pintado, J.M.; Departamento de Ciencia de Los Materiales e Ingenieria Metalurgica y Quimica Inorganica, University of Cádiz, Apdo. 40, Puerto Real (Cádiz) 11510, Spain; email: email@example.com, References: Trovarelli, A., (2002) Catalysis by Ceria and Related Materials, , 1st edition Imperial College Press London;
- [Show abstract] [Hide abstract] ABSTRACT: The evolution of the ceria-praseodymia mixed oxide promoter throughout the successive steps involved in the preparation of a 3% Rh/25% Ce0.8Pr0.2O2−x/Al2O3–3.5% SiO2 catalyst is studied with the help of X-ray diffraction (XRD), spatially resolved electron energy loss spectroscopy (EELS), XPS, and thermal programed desorption (TPD) techniques. Incipient wetness impregnation has been used to obtain the appropriate loading of this promoter. As revealed by XRD, EELS, and XPS data, the alumina-supported CeO2PrO2−x mixed oxide sample consisted of a bimodal distribution of the particles of the promoter. XRD shows two fluorite-like phases: cerium-rich particles with a mean crystallite size greater than 6 nm and smaller praseodymium-rich crystals, about 3.5 nm size. Surface Ce/Pr ratio obtained by XPS was consistent with a higher dispersion of the praseodymium-rich oxide particles. The final Rh catalyst was prepared in a second step, by impregnation of the CePrOx/Al2O3 system with an acidic solution of Rh(NO3)3. The low pH of this solution is responsible for further modifications of the lanthanide oxides distribution. Thus, there is a redispersion of the praseodymium-rich phase, which is evidenced by EELS and XPS data. Likewise, CO2 desorption from samples exposed to the atmosphere is consistent with an enhanced basicity of the sample due to the increase of Pr3+ content at the surface of the catalyst. The observed changes on the nanostructure of the mixed oxide promoter can be attributable to a partial dissolution of the oxide, selectively leaching Pr3+ cations from the lattice, which are finally deposited as small particles after the drying steps of the preparation. Copyright © 2008 John Wiley & Sons, Ltd.
- [Show abstract] [Hide abstract] ABSTRACT: In this study, we have investigated the redox deactivation of a Ce/Pr mixed oxide supported on modified alumina. Two samples have been prepared by using silica- or lanthana-modified alumina as supports: 25% Ce0.8Pr0.2O2−x/Al2O3-SiO2 and 25% Ce0.8Pr0.2O2−x/Al2O3-La2O3. The redox behavior was studied by reduction of the samples at selected temperatures, from 200 to 900 °C. Oxygen Storage Capacity (OSC) of reduced samples was measured by their reoxidation at 200 °C. The reduction degree attained by the supported mixed oxide, after reduction at temperatures up to 800 °C, increases in parallel for both samples. However, at 900 °C, there is a decrease of OSC, which is moderate for silica-modified sample, while for lanthana-modified catalyst, the OSC is almost negligible. XPS analysis of the fresh samples shows that the redox state of cerium cations close to the surface is mainly + 4, while praseodymium appears always as Pr3+. Samples reduced at different temperatures were also investigated by XPS. In the case of silica-modified alumina reduced at 900 °C, significant amounts of Ce4+ can still be detected, which is in good agreement with the OSC value observed at that temperature. However, lanthana-modified sample reduced at 800 °C shows an important amount of Ce3+, being the only oxidation state observed for cerium after reduction at 900 °C. This is in good agreement with the strong drop in OSC observed for this latter sample, which can be thus attributable to the trapping of trivalent cations by the alumina, forming a stable perovskite-like aluminate, LnAlO3, as confirmed by X-Ray Diffraction (XRD). Copyright © 2008 John Wiley & Sons, Ltd.
- [Show abstract] [Hide abstract] ABSTRACT: Cited By (since 1996): 1, Export Date: 6 February 2013, Source: Scopus, CODEN: SIAND, doi: 10.1002/sia.2773, Language of Original Document: English, Correspondence Address: Blanco, G.; Departamento de Ciencia de los Materiales e Ingenieria Metalürgica y Quimica Inorganica, University of Cádiz, Apdo 40 Puerto Real, Cádiz 11510, Spain; email: firstname.lastname@example.org, References: (2002) Catalysis by Ceria and Related Materials, , Trovarelli A ed, Imperial College Press: London;