Browsing by Author "Rojas, Rene"

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    ACTIVITY OF ALUMINA SUPPORTED Fe CATALYSTS FOR N2O DECOMPOSITION: EFFECTS OF THE IRON CONTENT AND THERMAL TREATMENT
    (2017) Alvarez, Pablo; Araya, Paulo; Rojas, Rene; Guerrero, Sichem; Aguila, Gonzalo
    The activity of Fe2O3/Al2O3 catalysts prepared by impregnation of Al2O3 with different amounts of Fe and calcination temperatures (650 and 900 degrees C) in the direct N2O decomposition reaction was studied. High calcination temperature was introduced to study the effect of "aging", which are the conditions prevailing in the process-gas option for N2O abatement. The catalysts were characterized by BET, XRD, UV-DRS, and H-2-TPR. The incorporation of Fe promotes the alumina phase transition (gamma-Al2O3 to alpha-Al2O3 ) when the catalysts are calcined at 900 degrees C, which is accompanied by a decrease in the specific area. The activity of the catalysts and the specific surface area depend on Fe loading and calcination temperature. It was found that highly dispersed Fe species are more active than bulk type Fe2O3 particles. We conclude that Fe2O3/Al2O3 catalysts prepared by impregnation method are active in the decomposition of N2O, to be used at low or high reaction temperatures (tail-gas or process-gas treatments, respectively), as part of nitric acid production plant.
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    Mono and bimetallic nickel bromide complexes bearing azolate-imine ligands: Synthesis, structural characterization and ethylene polymerization studies
    (ELSEVIER SCIENCE SA, 2009) Caris, Rodrigo; Peoples, Brian C.; Valderrama, Mauricio; Wu, Guang; Rojas, Rene
    The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When reacted with dibromo(2,2'-dimethoxyethylether) nickel(II) the complexes [NiBr2{N-(1-(3,5-dimethylpyrazol-1-yl) ethylidene)-2,6-diisopropylaniline}] (3) and [Ni2Br2(mu-Br)2{N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline} 2] (4) are yielded, respectively. The addition of MAO generates catalytically active species for the homopolymerization of ethylene. The polymer products were low molecular weight (3-6 K) and a monomodal molecular weight distribution, consistent with the presence of a single active site. In addition, the catalyst was found to efficiently oligomerize higher olefins to high molecular weights with narrow PDIs. (C) 2009 Elsevier B.V. All rights reserved.
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    New bis(azolylcarbonyl)pyridine chromium(III) complexes as initiators for ethylene polymerization
    (ELSEVIER SCIENCE SA, 2011) Hurtado, John; Ugarte, Javiera; Rojas, Rene; Valderrama, Mauricio; Mac Leod Carey, Desmond; Munoz Castro, Alvaro; Arratia Perez, Ramiro; Froehlich, Roland
    Reaction of 2,6-pyridinedicarbonyl dichloride with 3,5-dimethylpyrazole and 1H-indazole, respectively, yield the tridentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylcarbonyl)pyridine (1) and 2,6-bis(indazol-1-ylcarbonyl)pyridine (2). The molecular structure of the new compound (2) was determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)(3) in THF to form neutral complexes of general formula [CrCl3{2,6-bis(azolylcarbonyl)pyridine-N,N,N}] (3, 4) which were isolated in high yield as air stable green solids and characterized by elemental analysis, magnetic moment, IR, and mass spectroscopies. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active for the polymerization of ethylene. (C) 2011 Elsevier B.V. All rights reserved.
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    Nickel pre-catalysts bearing [(N)-imidoylamidine] ligands; influence of the presence of pyridine and pentafluorophenyl groups in ligand backbone on the reactivity in ethylene polymerizations
    (2012) Peoples, Brian C.; De la Vega, Gala; Valdebenito, Carolina; Quijada, Raul; Ibanez, Andres; Valderrama, Mauricio; Rojas, Rene
    In this contribution the synthesis and polymerization activity of the nickel complexes [NiBr2{N'-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenyl)acetamidine}] (2), [NiBr2{N'-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenylimine) ethylacetamidine}] (2a) and [NiBr2 {N-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)]-N-(pyridin-4-yl)acetamidine}] (3)are reported. The variation of the phenyl substituents on the beta amine was found to influence the polymerization activity of the complexes. The electron withdrawing/donating capacity of the substituted ring was found to be correlated with the polymerization activity, with the pentafluoro substituted ring increasing the polymerization activity and the pyridine ring decreasing the activity. The ligands and complexes were characterized using standard techniques and the polymer properties analyzed. (C) 2011 Elsevier B. V. All rights reserved.