Study of Pt/MCM-22 based catalysts in the transformation of n-hexane: effect of rare earth elements and mode of platinum introduction

The bifunctional transformation of n-hexane was carried out over Pt/MCM-22 based catalysts. MCM-22 was synthesized and submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb, followed by Pt introduction. Three different methods were used to introduce about 1 wt% of Pt in the zeolite: ion exchange, incipient wetness impregnation and mechanical mixture with Pt/Al(2)O(3). The bifunctional catalysts were characterized by transmission electron microscopy and by the model reaction of toluene hydrogenation. These experiments showed that, in the ion exchanged sample, Pt is located both within the inner micropores and on the outer surface, whereas in the impregnated one, the metal is essentially located on the outer surface under the form of large particles. The presence of RE elements increases the hydrogenating activity of Pt/MCM-22 since the location of these species at the vicinity of metal particles causes modification on its electronic properties. Whatever the mode of Pt introduction, a fast initial decrease in conversion is observed for n-hexane transformation, followed by a plateau related to the occurrence of the catalytic transformations at the hemicages located at the outer surface of the crystals. The effect of rare earth elements on the hydrogenating function leads to a lower selectivity in dibranched isomers and increased amounts of light products.

n-Hexane hydroisomerisation over bifunctional Pt/MCM-22 catalysts. Influence of the mode of Pt introduction

Three different methods were used to introduce 1.0 wt.% of Pt in bifunctional Pt/MCM-22 zeolite catalysts: ion exchange with Pt(NH3)(4)(2+), incipient wetness impregnation with PtCl6H2 and mechanical mixture with Pt/Al2O3. The Pt dispersion was estimated by transmission electron microscopy and the hydrogenating activity with toluene hydrogenation at 110 degrees C. From these experiments, it can be concluded that with the ion exchanged sample, platinum was located within the inner micropores and on the outer surface, whereas with the impregnated one, platinum was essentially on the outer surface under the form of large particles. With all the samples there is a fast initial decrease in the activity for n-hexane hydroisomerisation at 250 degrees C. With exchanged and impregnated samples, this decrease is followed by a plateau, the activity value being then higher with impregnated sample. For the sample prepared by mechanical mixture a continuous decrease in activity can be observed. All these differences can be related with the distinct locations of Pt.

Genotoxic effects of exposure to formaldehyde in two different occupational settings

Formaldehyde (CH2O), the most simple and reactive aldehyde, is a colorless, reactive and readily polymerizing gas at room temperature (National Toxicology Program [NTP]. It has a pungent suffocating odor that is recognized by most human subjects at concentrations below 1 ppm. Aleksandr Butlerov synthesized the chemical in 1859, but it was August Wilhelm von Hofmann who identified it as the product formed from passing methanol and air over a heated platinum spiral in 1867. This method is still the basis for the industrial production of formaldehyde today, in which methanol is oxidized using a metal catalyst. By the early 20th century, with the explosion of knowledge in chemistry and physics, coupled with demands for more innovative synthetic products, the scene was set for the birth of a new material–plastics. According to the Report on Carcinogens, formaldehyde ranks 25th in the overall U.S. chemical production, with more than 5 million tons produced each year. Formaldehyde annual production rises up to 21 million tons worldwide and it has increased in China with 7.5 million tons produced in 2007. Given its economic importance and widespread use, many people are exposed to formaldehyde environmentally and/or occupationally. Commercially, formaldehyde is manufactured as an aqueous solution called formalin, usually containing 37% by weight of dissolved formaldehyde. This chemical is present in all regions of the atmosphere arising from the oxidation of biogenic and anthropogenic hydrocarbons. Formaldehyde concentration levels range typically from 2 to 45 ppbV (parts per billion in a given volume) in urban settings that are mainly governed by primary emissions and secondary formation.

Synthesis, characterization, electrochemical behavior and in vitro protein tyrosine kinase inhibitory activity of the cymene-halogenobenzohydroxamato [Ru(eta(6)-cymene)(bha)Cl] complexes

The ruthenium(II)-cymene complexes [Ru(eta(6)-cymene)(bha)Cl] with substituted halogenobenzohydroxamato (bha) ligands (substituents = 4-F, 4-Cl, 4-Br, 2,4-F-2, 3,4-F-2, 2,5-F-2, 2,6-F-2) have been synthesized and characterized by elemental analysis, IR, H-1 NMR, C-13 NMR, cyclic voltammetry and controlled-potential electrolysis, and density functional theory (DFT) studies. The compositions of their frontier molecular orbitals (MOs) were established by DFT calculations, and the oxidation and reduction potentials are shown to follow the orders of the estimated vertical ionization potential and electron affinity, respectively. The electrochemical E-L Lever parameter is estimated for the first time for the various bha ligands, which can thus be ordered according to their electron-donor character. All complexes exhibit very strong protein tyrosine kinase (PTK) inhibitory activity, even much higher than that of genistein, the clinically used PTK inhibitory drug. The complex containing the 2,4-difluorobenzohydroxamato ligand is the most active one, and the dependences of the PTK activity of the complexes and of their redox potentials on the ring substituents are discussed. (C) 2012 Elsevier B.V. All rights reserved.

Catalytic behavior of alkali-treated Pt/HMOR n-hexane hydroisomerization

Bifunctional Pt-HMOR catalysts were prepared by incipient wetness impregnation of various desilicated MOR obtained by alkaline treatment using NaOH concentrations ranging from 0.1 to 0.5 M. The zeolite structural changes upon modification were investigated by several techniques including powder X-ray diffraction,Al-27 and Si-29 MAS-NMR spectroscopy, N-2 adsorption, pyridine adsorption followed by infrared spectroscopy and the catalytic model reaction of m-xylene transformation. For low alkaline concentration the zeolite acidity is preserved, along with a slight increase of the volume correspondent to the larger micropores due to the removal of extra-framework debris already existent at the parent zeolite. At higher NaOH concentrations there is a significant loss of crystalinity and acidity as well as the formation of mesoporosity. The characterization of the metal function shows similar patterns for Pt-HMOR and Pt-M/0.1 samples, with Pt particles located mainly inside the inner porosity. In contrast, large Pt particles become visible at the intercrystalline mesoporosity of MOR crystals developed during the desilication treatments at severe alkaline conditions. The catalytic results obtained for n-hexane hydroisomerization showed an improved selectivity for dibranched over monobranched isomers for Pt-M/0.1 sample, likely due to the preservation of the support acidity and the slight enlargement of the micropores. This work is a new example in which the mesoporous development does not improve the catalytic efficiency of the zeolites, whereas mild alkaline desilication might be considered as an effective solution to produce customized catalysts with enhanced performance for a given application. (C) 2014 Elsevier B.V. All rights reserved.

Baeyer-Villiger oxidation of Keotones catalysed by rhenium complexes bearing N- Or Oxo-Ligands

Rhenium (I, III-V or VII) complexes bearing N-donor or oxo-ligands catalyse the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g. 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone and 3,3-dimethyl-2-butanone) into the corresponding lactones or esters, in the presence of aqueous H2O2 (30%). The effects of various reaction parameters are studied allowing to achieve yields up to 54%.

Pt/Carbon materials as Bi-Functional catalysts for N-decane hydroisomerization

The activity and selectivity of bi-functional carbon-supported platinum catalysts for the hydroisomerization of n-alkanes have been studied. The influence of the properties of the carbon support on the performance of the catalysts were investigated by incorporating the metallic function on a series of carbons with varied porosity (microporous: GL-50 from Norit, and mesoporous: CMK-3) and surface chemistry (modified by wet oxidation). The characterization results achieved with H-2 chemisorption and TEM showed differences in surface metal concentrations and metal-support interactions depending on the support composition. The highest metal dispersion was achieved after oxidation of the carbon matrix in concentrated nitric acid, suggesting that the presence of surface functional sites distributed in inner and outer surface favors a homogeneous metal distribution. On the other hand, the higher hydrogenating activity of the catalysts prepared with the mesoporous carbon pointed out that a fast molecular traffic inside the pores plays an important role in the catalysts performance. For n-decane hydroisomerization of long chain n-alkanes, higher activities were obtained for the catalysts with an optimized acidity and metal dispersion along with adequate porosity, pointing out the importance of the support properties in the performance of the catalysts.

A farmacogenética e a medicina personalizada

A farmacogenética tem por objetivo a identificação de diferenças genéticas entre indivíduos que possam influenciar a resposta à terapêutica farmacológica, melhorando a sua eficácia e segurança. Associado à farmacogenética surge a “medicina personalizada”, ou seja, em oposição à existência de um fármaco que consiga tratar todos os pacientes, o tratamento individualizado parece o caminho mais promissor, uma vez que reduz o risco de reações adversas por toxicidade (segurança), adequa a dose ao indivíduo, evitando excessos ou défices (dose) e evita a metodologia de tentativa erro na escolha do fármaco (eficácia). A farmacogenética é relevante para a resposta individual ao fármaco por duas vias distintas: a farmacocinética e a farmacodinâmica. A variabilidade genética pode afetar a forma como um fármaco pode ser absorvido, ativado, metabolizado ou excretado, podendo conduzir assim a uma variabilidade na resposta. De entre o número infindável de possíveis exemplos, nesta revisão apresentam-se exemplos relacionados com os genes do Citocromo P450, do gene NAT2 e do gene da Colinesterase. As diferenças genéticas entre os indivíduos podem ainda afetar a resposta ao fármaco pela sua farmacodinâmica, ou seja, a resposta específica do alvo ao fármaco. De entre a multiplicidade de alvos de fármacos existentes serão apresentados exemplos do gene da G6PD e do VKORC1. Apesar de alguns dados científicos indicarem benefício para o paciente, ainda está longe de a farmacogenética fazer parte da prática clínica de rotina, talvez porque os custos-benefícios ainda não foram avaliados de forma precisa.

Hydrogenating activity of Pt/zeolite catalysts focusing acid support and metal dispersion influence

Toluene hydrogenation was studied over catalysts based on Pt supported on large pore zeolites (HUSY and HBEA) with different metal/acid ratios. Acidity of zeolites was assessed by pyridine adsorption followed by FTIR showing only small changes before and after Pt introduction. Metal dispersion was determined by H2–O2 titration and verified by a linear correlation with the intensity of Pt0–CO band obtained by in situ FTIR. It was also observed that the electronic properties of Pt0 clusters were similar for the different catalysts. Catalytic tests showed rapid catalyst deactivation with an activity loss of 80–95% after 60 min of reaction. The turnover frequency of fresh catalysts depended both on metal dispersion and the support. For the same support, it changed by a 1.7-fold (HBEA) and 4.0-fold (HUSY) showing that toluene hydrogenation is structure-sensitive, i.e. hydrogenating activity is not a unique function of accessible metal. This was proposed to be due to the contribution to the overall activity of the hydrogenation of adsorbed toluene on acid sites via hydrogen spillover. Taking into account the role of zeolite acidity, the catalysts series were compared by the activity per total adsorbing sites which was observed to increase steadily with nPt/(nPt + nA). An increase of the accessible Pt atoms leads to an increase on the amount of spilled over hydrogen available in acid sites therefore increasing the overall activity. Pt/HBEA catalysts were found to be more active per total adsorbing site than Pt/HUSY which is proposed to be due to an augmentation in the efficiency of spilled over hydrogen diffusion related to the proximity between Pt clusters and acid sites. The intervention of Lewis acid sites in a greater extent than that measured by pyridine adsorption may also contribute to this higher activity of Pt/HBEA catalysts. These results reinforce the importance of model reactions as a closer perspective to the relevant catalyst properties in reaction conditions.