Olefin Purification and Selective Hydrogenation of Alkynes with Low Loaded Pd Nanoparticle Catalysts

The catalytic performance of Pd-nanoparticle catalysts for the selective hydrogenation of alkynes at mild conditions (150 kPa and 303 K) was evaluated. A Lindlar commercial catalyst was also tested for comparison. The effects of acidity, amount of active sites and dispersion on the catalytic activity and selectivity were studied. At mild conditions, Pd-nanoparticle catalysts were considerably more active and slightly more selective than the Lindlar catalyst. The best synthesized catalyst for the purification of 1-pentene was Pd/Al2O3-Mg (r0 = 41.1 mol gPd–1 min–1, 94% selectivity). The activity and selectivity of Pd/CaCO3 were similar to those of the Lindlar catalyst. The smallest particle sizes (3–4.5 nm) favored the dissociative adsorption of hydrogen over Pd° active sites and a good catalytic behavior. The weaker acid centers (Lewis) of Pd/Al2O3-Mg and Pd/CaCO3 favored higher selectivities to the desired alkene. Pd/Al2O3 was the most active catalyst but also the least selective. This was due to strong acid sites, remnant Bronsted acid sites, which provide extra hydrogen that favors the alkyne hydrogenation rate and also the undesired overhydrogenation of the alkene and/or the isomerization.The financial support provided by UNL (Grants CAI+D 50420150100074LI and 50420150100028LI), CONICET (Grant PIP 11220130100457CO), and ANPCyT (Grant PICT 2016 1453) are acknowledged

Metal and precursor effect during 1-heptyne selective hydrogenation using an activated carbon as support

Palladium, platinum, and ruthenium supported on activated carbon were used as catalysts for the selective hydrogenation of 1-heptyne, a terminal alkyne. All catalysts were characterized by temperature programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. TPR and XPS suggest that the metal in all catalysts is reduced after the pretreatment with H2 at 673 K. The TPR trace of the PdNRX catalyst shows that the support surface groups are greatly modified as a consequence of the use of HNO3 during the catalyst preparation. During the hydrogenation of 1-heptyne, both palladium catalysts were more active and selective than the platinum and ruthenium catalysts. The activity order of the catalysts is as follows: PdClRX > PdNRX > PtClRX ≫ RuClRX. This superior performance of PdClRX was attributed in part to the total occupancy of the d electronic levels of the Pd metal that is supposed to promote the rupture of the H2 bond during the hydrogenation reaction. The activity differences between PdClRX and PdNRX catalysts could be attributed to a better accessibility of the substrate to the active sites, as a consequence of steric and electronic effects of the superficial support groups. The order for the selectivity to 1-heptene is as follows: PdClRX = PdNRX > RuClRX > PtClRX, and it can be mainly attributed to thermodynamic effects.UNL and CONICET

Role of the support and chloride during the purification of 1‐pentene in alkyne/alkene streams over Pd catalysts

BACKGROUND: Pd nanoparticles over different supports were evaluated during the alkyne selective hydrogenation of medium chain (C7 and C5) and the 1‐pentene purification at mild operational conditions (150 kPa and 303 K). The role of support and chloride was investigated; γ‐Al2O3, γ‐Al2O3 modified with Mg, CaCO3 and activated carbon were used as supports, and PdCl2 as precursor salt. The classical Lindlar catalyst was used as reference. RESULTS: Surface acidity of supports, active sites dispersion and surface species (MgO, PdxClyOz and/or functional groups) can favor or disfavor the desorption of 1‐alkene during the purification of 1‐pentene stream. The smallest particle sizes (3.8–10.0 nm) favor the dissociative adsorption of hydrogen over Pd° active sites, promoting good catalytic behavior. The best synthesized catalysts are Pd/Al–Mg and Pd/Ca, and their high selectivity (≥90%) is favored by the presence of superficial acidic Lewis sites. On the contrary, lower selectivity (74–80%) is assessed on catalysts with Brönsted acidic sites (Pd/Al and Pd/RX3) that favored the undesired overhydrogenation or isomerization reactions. CONCLUSION: The geometric and electronic properties of the support have a major influence on the activity and selectivity of the catalysts. Low loaded Pd catalysts supported on Al2O3‐Mg and CaCO3 (Pd/Al‐Mg, Pd/Ca) can be used for the purification of medium or large terminal alkenes at mild reaction conditions as an alternative to the toxic Lindlar commercial catalyst.The financial support provided by Universidad Nacional del Litoral (UNL, Grants CAI+D), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Grant PIP 11220130100457CO), and Agencia Nacional de Promoción de Ciencia y Tecnológica (ANPCyT, Grants PICT 2016 and 2020) are acknowledged. L. García thanks Ministerio de Ciencia Tecnología e Innovación de Colombia (Minciencias, Call 860, for Doctorates abroad 2019)

Graphite oxide as a support for palladium and rhodium complexes, assessed as catalysts for the partial hydrogenation of 1-heptyne

Graphite oxide (GO) was used to anchor [PdCl2(TDA)2] and [RhCl(TDA)3] (TDA =NH2(CH2)12CH3) with 2wt % of metal load. Elemental analysis (EA), FTIR, XPS, XRD and atomic absorption spectroscopy (AA) were the techniques employed for characterization. FTIR and XRD revealed that both complexes were mainly immobilized on the GO surface. The partial hydrogenation of 1-heptyne was the test reaction to evaluate the catalytic behavior of these heterogenized complexes under mild conditions of temperature and pressure in a semi continuous process. The results were compared with those obtained with the Wilkinson catalyst under the same operational conditions. AA analysis revealed that there is no leaching of the complexes during the heterogeneous catalytic evaluations. [RhCl(TDA)3]/GO was the best catalyst due to electronic and steric effects as well as the influence of the support

La renovación de la palabra en el bicentenario de la Argentina : los colores de la mirada lingüística

El libro reúne trabajos en los que se exponen resultados de investigaciones presentadas por investigadores de Argentina, Chile, Brasil, España, Italia y Alemania en el XII Congreso de la Sociedad Argentina de Lingüística (SAL), Bicentenario: la renovación de la palabra, realizado en Mendoza, Argentina, entre el 6 y el 9 de abril de 2010. Las temáticas abordadas en los 167 capítulos muestran las grandes líneas de investigación que se desarrollan fundamentalmente en nuestro país, pero también en los otros países mencionados arriba, y señalan además las áreas que recién se inician, con poca tradición en nuestro país y que deberían fomentarse. Los trabajos aquí publicados se enmarcan dentro de las siguientes disciplinas y/o campos de investigación: Fonología, Sintaxis, Semántica y Pragmática, Lingüística Cognitiva, Análisis del Discurso, Psicolingüística, Adquisición de la Lengua, Sociolingüística y Dialectología, Didáctica de la lengua, Lingüística Aplicada, Lingüística Computacional, Historia de la Lengua y la Lingüística, Lenguas Aborígenes, Filosofía del Lenguaje, Lexicología y Terminología

Hidrogenación selectiva en fase liquida de 1-heptino sobre Ni/Al2O3. Efecto de la temperatura de reacción

In this work, it was studied the effect of reaction temperature during selective hydrogenation of 1-heptyne to 1- heptene. Supported nickel on ã -alumina was used as catalyst. Different operation temperatures (273, 303 and 323 K) were evaluated and the best behavior was found at the higher reaction temperature, showing high selectivity (c.a. 90 %). The prepared nickel catalyst can be seen as a cheaper alternative to industrial level compared to known palladium catalysts, not only due to the lower cost of metal, but also because of its small metal loading (3,6 % mass). The catalyst was characterized by X-Ray Diffraction, Temperature Programmed Reduction and X-Ray Photoelectron Spectroscopy. These different techniques indicated the presence of nickel oxide with support strong interactions at bulk level, and the presence of electron-deficient species of nickel at surface level, which were the active species during the hydrogenation of the terminal alkyne.En este trabajo fue evaluado el efecto de la temperatura de reaccion en la hidrogenacion selectiva de 1-heptino a 1-hepteno usando un catalizador de niquel soportado sobre �Á -alumina. Fueron estudiadas diferentes temperaturas operacionales (273, 303 y 323 K), obteniendose mayor conversion total del reactivo a la mayor temperatura, con una selectividad proxima al 90%. El catalizador de niquel preparado puede considerarse como una alternativa mas economica a nivel industrial frente a los ya conocidos catalizadores de paladio, no solo debido al bajo costo del metal sino tambien debido a su bajo contenido metalico (3,6% en masa). El catalizador fue caracterizado por Difraccion de Rayos X, Reduccion a Temperatura Programada y Espectroscopia Fotoelectronica de Rayos X. Estas indicaron la presencia de oxido de niquel a nivel masico con fuertes interacciones con el soporte y la existencia de especies electro-deficientes de niquel a nivel superficial quienes serian las especies activas durante la hidrogenacion del alquino terminal

Hydrogenation of diacetyl over composite-supported egg-shell noble metal catalysts

Two composite supports with a mixed inorganic–organic structure were synthesized: BTAl and UTAl. Hydrophilic–hydrophobic dual properties of the supports were suitable for preparing egg-shell-supported metal catalysts for selective hydrogenation reactions. The catalysts were characterized by ICP, XRD, OM, TEM, EPMA, XPS and TGA. Their mechanical resistance was assessed. Activity and selectivity were tested with the hydrogenation of 2,3-butanedione (diacetyl) to 3-hydroxy-2-butanoneacetoin (acetoin). The same order of increasing metal particle size was found for the two tested supports: Pt < Ru < Pd. The XPS analysis showed that the metal/composite catalysts reduced in H2 at 503 K had two kinds of active sites: reduced (Me°) and electron-deficient (Me+). It was rationalized that the hydrogen bond cleavage was performed on the Me° active sites, while reactant adsorption occurred on the Me+ sites. The differences in activity and selectivity between the composite catalysts were attributed to electronic effects on the different metals and to different adsorptive properties of the different polymers. The high selectivity to acetoin was attributed to the preferential adsorption of diacetyl as compared to the adsorption of acetoin. The BTAl catalysts were slightly more active and selective than the UTAl ones. This was attributed to electronic effects caused by remnant organic groups on the composite supports (urethane or biphenyl on UTAl or BTAl, respectively). Pd-BTAl was the most active and selective catalyst, a fact related to electronic effects of both palladium and the support.We thank CONICET, ANPCyT and UNL for the financial assistance of this work (Grants PIP 112-201101-00410 and 112-201301-00457, PICT and CAI + D)

Sulfur resistance of Pt-W catalysts

The sulfur resistance of low-loaded monometallic Pt catalysts and bimetallic Pt-W catalysts during the partial selective hydrogenation of styrene, a model compound of Pygas streams, was studied. The effect of metal impregnation sequence on the activity and selectivity was also evaluated. Catalysts were characterized by ICP, TPR, XRD, and XPS techniques. Catalytic tests with sulfur-free and sulfur-doped feeds were performed. All catalysts showed high selectivities (>98%) to ethylbenzene. Activity differences between the catalysts were mainly attributed to electronic effects due to the presence of different electron-rich species of Pt0 and electron-deficient species of Ptδ+. Pt0 promotes the cleavage of H2 while Ptδ+ the adsorption of styrene. The catalyst successively impregnated with W and Pt (WPt/Al) was more active and sulfur resistant than the catalyst prepared with an inverse impregnation order (PtW/Al). The higher poison resistance of WPt/Al was attributed to both steric and electronic effects.UNL, CONICET, and ANPCyT

Influence of ni addition to a low-loaded palladium catalyst on the selective hydrogenation of 1-heptyne

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

In Situ DRIFTS Analysis during Hydrogenation of 1-Pentyne and Olefin Purification with Ag Nano Particles

The catalytic performance of nanoparticles (NPs) of Ag anchored on different supports was evaluated during the selective hydrogenation of 1-pentyne and the purification of a mixture of 1-pentene/1-pentyne (70/30 vol %). The catalysts were identified: Ag/Al (Ag supported on ɣ-Al2O3), Ag/Al-Mg (Ag supported on ɣ-Al2O3 modified with Mg), Ag/Ca (Ag supported on CaCO3) and Ag/RX3 (Ag supported on activated carbon-type: RX3). Besides, in situ DRIFTS analysis of 1-pentyne adsorption on each supports, catalysts and 1-pentyne hydrogenation were investigated. The results showed that the synthesized catalysts were active and very selective (≥85%) for obtaining the desired product (1-pentene). Different adsorbed species (-CºC- and -C=C-) were observed on the supports and catalysts surface using in situ DRIFT analysis, which can be correlated to the activity and high selectivity reached. The role of the supports and electronic properties over Ag improve to H2 dissociative chemisorption during the hydrogenation reactions; promoting the selectivity and the high catalytic performance. Ag/Al and Ag/Al-Mg were the most active catalysts. This was due to the synergism between the active Ag°/Ag+ species and the supports (electronic effects). The results show that Ag/Al and Ag/Al-Mg catalysts have favorable properties and are promising for the alkyne hydrogenation and olefin purification reactions