The effect of noble metal catalysts supported on an ionic exchange resin for the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate was studied. High activity and moderate enantioselectivity levels were obtained. Pt was the best enantioselective metallic phase, followed by Pd and Au; Rh was the less enantioselective metallic phase. The effect of the active site was evaluated for the most enantioselective catalyst: 2Pt-WA30 (prefix indicates the metal loading). A novel method for sintering the Pt metal particles by nitriles reduction was used, and a controlled migration of the metal particles to the surface layers was observed. There existed an optimal particle size with maximization of the enantiomeric excess, corresponding to 24 h sintering. The hydrogenation of ethyl pyruvate to ethyl lactate was found to be structure-sensitive and the importance of the metal particle size for the adsorption of the chiral modifier was proved. Two different chirality induction methods were tried for the 2Pt-WA30 catalyst: (i) the addition of the chiral modifier (CM) to the reaction media, or (ii) the modification of the catalyst in a swelling medium prior to the reaction in order to encapsulate CM. Lower activity but higher enantioselectivity levels were obtained with method (ii). Finally, the reuse of the catalysts was also assessed by means of consecutive reaction tests.

The influence of the kind of metal precursor and the sequence of impregnation on the properties of Pd-Ni catalysts was evaluated during the test reaction of selective hydrogenation of styrene to ethylbenzene by means of physicochemical characterization. The focus was put on the final hydrogenating activity and the resistance to deactivation by sulfided compounds (thiophene). The used techniques of characterization were ICP, XPS, XDR, TPR, CO chemisorption and TEM. XPS results indicated the presence of different Pd species: Pdδ-, Pdº and Pdδ+. In the case of the Ni containing catalysts, Niº and NiO species were also detected. These palladium and nickel species would be responsables of the variation of activity and sulfurresistance of the catalysts. NiClPd catalysts had a higher resistance to deactivation by sulfur poisoning. This was associated to a higher concentration of Pdη+ClxOy species that would prevent the adsorption of thiophene by both steric and electronic effects. It could also be due to the lower concentration of Pdº and Niº on these catalysts, as compared to those shown by the PdNiCl catalysts. Both the Pdº and Niº species are more prone to poisoning because of their higher electronic availability.

Resumen En este trabajo se estudió la transformación en fase líquida de 5 hidroximetilfurfural (5-HMF) a ácido 2,5-furandicarboxilico con el uso de catalizadores de Pt y Pd soportados en carbón activado con la presencia de NaOH ó CaCO3. Los catalizadores fueron caracterizados por quimisorción de H2 a temperatura ambiente, espectroscopia de rayos X (XPS) y análisis termogravimétrico (TGA). Los resultados indican que el tamaño de partícula de los catalizadores sigue el orden PtCl/C < PdCl/C < PdN/C el cual está estrechamente relacionado con la actividad catalítica. Se encontró que las partículas metálicas están presentes como especies de Pd0 and Pt0. Siendo el catalizador de Pt-Cl/C con el uso de CaCO3 como aditivo.

Abstract The liquid phase transformation of 5-hydroxymethylfurfuraldehyde (5-HMF) towards 2,5-furandicarboxylic acid (2,5-FDCA) using Pt and Pd catalysts supported on activated carbon and with the presence of CaCO3 and NaOH, is reported. The catalysts were characterized using different techniques, such as: H2 chemisorption at room temperature, X ray photoelectronic spectroscopy (XPS) and thermogravimetric analysis (TGA). The results indicate that the particle size followed the order: PtCl/C < PdCl/C < PdN/C, which is closely related to the catalytic behavior. It was found that the metal particles are present in the Pd0 and Pt0 form. PtCl/C was most active catalyst using CaCO3 as weak base.

The Wilkinson complex was tested as a catalyst in the partial hydrogenation of 1-heptyne, a medium chain alkyne, at a temperature of T = 303 K and hydrogen pressure PH2 = 150 kPa. The tests were performed in homogeneous system as well as heterogeneous system, supporting the complex on i) γ-Al2O3 and ii) a commercial carbonaceous material, RX3. Characterization by means of XPS and FTIR revealed that the anchored complex did not lose its chemical identity, being the catalytically active species. The Wilkinson complex on RX3 showed better conversions and selectivities, higher than the Lindlar catalyst, used as a reference. Additionally, it was proposed a method to recover Rh as a metal from the remaining solutions, and from it regenerate the complex to be reused from it.

Low-cost tungsten monometallic catalysts containing variable amounts of metal (4.5, 7.1 and 8.5%W) were prepared by impregnating alumina with ammonium metatungstate as an inexpensive precursor. The catalysts were characterized using ICP, XPS, XRD, TPR and hydrogen chemisorption. These techniques revealed mainly WO3-Al2O3 (W6+) species on the surface. The effects of the content of W nanoparticles and reaction temperature on activity and selectivity for the partial hydrogenation of 3-hexyne, a non-terminal alkyne, were assessed under moderate conditions of temperature and pressure. The monometallic catalysts prepared were found to be active and stereoselective for the production of (Z )-3-hexene, had the following order: 7.1WN/A > 8.5 WN/A ≥ 4.5 WN/A. Additionally, the performance of the synthesized xWN/A catalysts exhibited high sensitivity to temperature variation. In all cases, the maximum 3-hexyne total conversion and selectivity was achieved at 323 K. The performance of the catalysts was considered to be a consequence of two phenomena: a) the electronic effects, related to the high charge of W (+6), causing an intensive dipole moment in the hydrogen molecule (van der Waals forces) and leading to heterolytic bond rupture; the H+ and H- species generated approach a 3-hexyne adsorbate molecule and cause heterolytic rupture of the C≡C bond into C- = C+; and b) steric effects related to the high concentration of WO3 on 8.5WN/A that block the Al2O3 support. Catalyst deactivation was detected, starting at about 50 min of reaction time. Electrodeficient W6+ species are responsible for the formation of green oil at the surface level, blocking pores and active sites of the catalyst, particularly at low reaction temperatures (293 and 303 K). The resulting best catalyst, 7.1WN/A, has low fabrication cost and high selectivity for (Z )-3-hexene (94%) at 323 K. This selectivity is comparable to that of the classical and more expensive industrial Lindlar catalyst (5 wt% Pd). The alumina supported tungsten catalysts are low-cost potential replacements for the Lindlar industrial catalyst. These catalysts could also be used for preparing bimetallic W-Pd catalysts for selective hydrogenation of terminal and non-terminal alkynes.

Two complexes of Rh(I) and Pd(II) with chloride and tridecylamine ligands were obtained and characterized by Elementary Analysis and by XPS and FTIR spectroscopies. Complexes anchored on γ-Al2O3 were tested in the styrene semi-hydrogenation reaction carried out in the absence or presence of a sulfur poison. Although both low loaded catalysts were highly selective, the Pd(II) complex was three times more active than the Rh(I) complex. The rhodium complex was more sulfur resistant but less active than the palladium complex. Differences in conversion and sulfur resistance between both complexes could be related to electronic and/or geometric effects.

Semi-hydrogenation of alkynes has industrial and academic relevance on a large scale. To increase the activity, selectivity and lifetime of monometallic catalysts, the development of bimetallic catalysts has been investigated. 1-Heptyne hydrogenation over low-loaded Pd and Ni monometallic and PdNi bimetallic catalysts was studied in liquid phase at mild conditions. XPS results suggest that nickel addition to Pd modifies the electronic state of palladium as nickel loading is increased. Low-loaded Pd catalysts showed the highest selectivities (> 95%). The most active prepared catalyst, PdNi(1%), was more selective than the Lindlar catalyst.

A series of Group VIII metal catalysts was obtained for the semi-hydrogenation of styrene. Catalysts were characterized by Hydrogen Chemisorption, TPR and XPS. Palladium, rhodium and platinum low metal loading prepared catalysts presented high activity and selectivity (ca. 98%) during the semi-hydrogenation of styrene, being palladium the most active catalyst. The ruthenium catalyst also presented high selectivity (ca. 98%), but the lowest activity. For the palladium catalyst, the influence of the precursor salt and of the reduction temperature on the activity and selectivity were studied. The following activity series was obtained: PdN-423 > PdCl-673 > PdCl-373> PtCl-673 > RhCl-673 >> RuCl-673. As determined by XPS, differences in activity could be attributed, at least in part, to electronic effects.

Pocos estudios cualitativos proveen información acerca del fenómeno de la integración de Tecnologías de Información y Comunicaciones (TIC) en educación superior. Este documento corresponde a uno de los 17 estudios de caso adelantados en una investigación adelantada para conocer más a profundidad este fenómeno e identificar aprendizajes de los estudiantes que participan de él. Los datos se recogieron a partir de observaciones no participantes a las clases durante un semestre académico, entrevistas semiestructuradas a la profesora y entrevistas y grupos focales con estudiantes. Adicionalmente se analizaron los trabajos de los estudiantes realizados con apoyo de TIC. Los datos fueron analizados mediante categorías deductivas e inductivas comunes a todos los casos y finalmente contextualizados. El caso descrito en este artículo se refiere al ambiente de aprendizaje construido por 16 estudiantes y su profesora donde se integraron las TIC coherentemente con la estrategia pedagógica pero no agregaron valor al proceso de aprendizaje. La descripción presenta patrones de comportamiento, concepciones y prácticas pedagógicas que para otros profesores pueden constituirse en elementos para tomar decisiones sobre cómo diseñar sus ambientes de aprendizaje con TIC y para motivarlos a reflexionar sobre sus propias prácticas pedagógicas.

A few qualitative studies provide information about the integration of Information and Communication Technologies (TIC) into higher education. This article corresponds to one of the 17 case studies carried out in a research to know about this phenomenon more deeply and to identify the learning process of the students who participated in it. The data was collected from nonparticipant class observations to the classes in an academic semester, semi-structured interviews to the teacher and interviews and targeted groups with students. Additionally the works of the students were analyzed with the support of TIC's. The data was analyzed with common deductive and inductive categories that were common to all the cases and was finally contextualized. The case described in this article talks about the learning environment constructed by 16 students and their professor, where she coherently integrated the TIC with her pedagogical strategy but did not add value to the learning process. The description presents behavior patterns, conceptions and pedagogical practices that other teachers can use as elements to make decisions about how to design their learning environments with TIC and to motivate them to reflect on their own pedagogical practices.

Poucos estudos qualitativos fornecem informação acerca do fenômeno de integração de Tecnologias de Informação e Comunicações (TIC) na educação superior. Este documento corresponde a um dos 17 estudos de caso realizados numa pesquisa com o objetivo de conhecer com mais profundidade este fenômeno e identificar as aprendizagens dos estudantes que participaram nele. Os fatos foram recolhidos a partir de observações não participantes nas aulas durante um semestre acadêmico, entrevistas semi-estruturadas à professora e entrevistas e grupos focais com estudantes. Adicionalmente analisaram-se os trabalhos dos estudantes realizados com apoio das TIC. Os dados foram analisados mediante categorias dedutivas e indutivas comuns a todos os casos e depois foram contextualizados. O caso descrito neste artigo refere-se ao ambiente de aprendizagem construído por 16 estudantes e sua professora, onde foram integradas as TIC coerentemente com a estratégia pedagógica, mas não agregaram nenhum valor ao processo de aprendizagem. Esta descrição apresenta padrões de comportamento, conceições e práticas pedagógicas que para os outros professores podem constituir-se em elementos para a toma de decisões sobre como desenhar ambientes de aprendizagem com TIC e para motivá-los a refletir sobre as suas próprias práticas pedagógicas.