Evaluation of Catalysts for the Metathesis of Ethene and 2-Butene to Propene

Different metathesis catalysts were evaluated regarding their activity for propene production from ethene and trans-butene feedstocks. Nickel, molybdenum, rhenium and tungsten, along with bimetallic nickel-rhenium systems were applied with commercial supports and self-synthesized MCM-41. For the latter support the Si/Al ratio was adjusted as an additional optimization parameter (Si/Al = 60). Attractive activities were observed using Re and NiRe based catalysts at moderate temperatures of 200–250 °C. In contrast, the tungsten-based catalysts were only active above 450 °C. Three catalysts, namely Re/AlMCM-41(60), NiRe/mix (1:1) and W/SiO2 offered propene selectivity’s exceeding 40% at attractive conversion rates. These catalysts were characterized by BET, powder XRD, NH3-TPD and TPR-TPO-TPR cycles. At specific reaction temperatures, reaction-regeneration cycles were performed, which revealed that for the Re and W catalysts the initial reactant conversions and propene selectivity can be recovered. In contrast, for the NiRe catalyst, a continuous, gradual and irreversible decrease of activity was observed. Even though the tungsten catalyst was operated at the highest temperature, no irreversible decrease in conversion and propene selectivity occurred. Therefore, this catalyst has potential as a promising candidate for the synthesis of propene

Corrigendum to ‘‘Alumino-mesostructured Ni catalysts for the direct conversion of ethene to propene” [J. Catal. 305 (2013) 154–168]

Ni/MCM-41 and Ni/AlMCM-41 were synthesized at different Si/Al ratios and tested in the direct conversion of ethene to propene (ETP-reaction). It was intended to evaluate the effect of modifying the catalyst acidity on the ETP-reaction rather than optimizing its performance. All catalysts were characterized by powder XRD, N2-physisorption, 29Si and 27Al MAS NMR, TEM, NH3-TPD, pyridine-DRITFS, H2-TPR, and TPO. Ni/MCM-41 showed low catalytic activity due to its low acidity. Ni/AlMCM-41 catalyst with a Si/Al ratio of 60 had high catalytic activity. Characterization results revealed that the catalyst structure does not have effect on the catalytic activity. Al could be incorporated into the MCM-41 framework up to Si/Al ratio of 16. Two different Ni-composites on the surface of the MCM-41 and AlMCM-41 were observed. Deeper characterization is required to know the Ni state. Important deactivation was observed at 450 °C. The nature of the carbonaceous species and reaction mechanism require deeper characterization

Análisis morfométrico y funcional de ovocitos bovinos obtenidos de ovarios de matadero y por aspiración folicular transvaginal en vacas criollas del altiplano ecuatoriano

This study assessed the morphometric and functional characteristics of oocytes from 10 native cows to the Ecuadorian Andes, collected by transvaginal follicular aspiration (OPU) and oocytes collected post mortem (PM) from abattoir ovaries. For this purpose, 1157 cumulus-oocyte complexes (CCOs) of the OPU group (n=271) and PM group (n=886) were recovered in 10 repetitions per group by follicular aspiration at 90 mm Hg pressure and classified as A, B or C, according to the characteristics of the cytoplasm and cumulus cells. The activity of the enzyme glucose 6 phosphate dehydrogenase (G6PD) was determined as an indicator of follicular growth and maturation and the integrity of the plasma membrane by staining the CCOs with cresyl brilliant blue (BCB +) and trypan blue, respectively. The size (diameter and volume) of the oocytes was evaluated using CaptaVisio® software v. 5.1. The data were analysed by logistic regression and by the SAS general linear model, and the means were compared by the least square method. The results showed that the oocytes of the PM group had a larger diameter (126.0 ± 0.48 vs. 122.7 ± 0.79 µm; p<0.01) and integrity of the plasma membrane (86.0 vs. 76.8%; p<0.05) than the OPU group. However, quality A and B oocytes did not show significant differences between groups with respect to plasma membrane integrity and BCB + values. The results suggest that, although the fact that the size and viability were more affected in the oocytes aspirated by OPU, those of quality A and B from both sources showed similar values regarding the integrity of the plasma membrane and metabolic condition to continue. maturation.El estudio analizó las características morfométricas y funcionales de ovocitos de 10 vacas nativas de los Andes ecuatorianos, colectados por aspiración folicular transvaginal (OPU) y de ovocitos colectados post mortem (PM) de ovarios de matadero. Para este propósito, 1157 complejos cúmulo-ovocito (CCOs) del grupo OPU (n=271) y PM (n=886) fueron recuperados en 10 repeticiones por grupo por aspiración folicular a 90 mm Hg de presión y clasificados en calidad A, B o C, de acuerdo con las características del citoplasma y células del cúmulo. Se determinó la actividad de la enzima glucosa 6 fosfato deshidrogenasa (G6PD) como indicador de crecimiento folicular y maduración finalizado y la integridad de la membrana plasmática tiñendo los CCOs con azul brillante de cresilo (BCB+) y azul de tripán, respectivamente. Se evaluó el tamaño (diámetro y volumen) de los ovocitos usando un software CaptaVisionÒ (v. 5.1). Los datos se analizaron por regresión logística y por el modelo lineal general del SAS, y las medias se compararon por el método de los mínimos cuadrados. Los resultados mostraron que los ovocitos del grupo PM presentaron mayor diámetro (126.0±0.48 vs 122.7±0.79 µm; p<0.01) e integridad de la membrana plasmática (86.0 vs 76.8%; p<0.05) que el grupo OPU. Sin embargo, los ovocitos de calidad A y B no registraron diferencias significativas entre grupos con respecto a la integridad de la membrana plasmática y valores de BCB+. Los resultados sugieren que, a pesar de que el tamaño y la viabilidad fue más afectada en los ovocitos aspirados por OPU, los de calidad A y B provenientes de ambas fuentes mostraron valores similares con respecto a la integridad de la membrana plasmática y condición metabólica para proseguir la maduración

Experimental study of the deactivation of Ni/AlMCM-41 catalyst in the direct conversion of ethene to propene

In this work, an experimental study of the deactivation and regarding a possible regeneration procedure in the ETP-reaction using Ni/AlMCM-41 (Si/Al = 60) was carried out. ETP experiments at different temperatures and long time on-stream were carried out. Characterization of the catalyst after experiments was performed using powder-XRD, N2-physisorption, NH3-TPD, TPO and TEM. At 250 and 350 ◦C the catalyst did not suffer significant deactivation after 107 h on-stream. Nevertheless, the yield of propene was low. A severe deactivation of the catalyst was observed at 450 ◦C where propene was the main reaction product. Regeneration of the catalyst after 30 h on-stream at temperatures lower than 350 ◦C could be performed using a mixture of 5 vol.% oxygen in N2. The regeneration of the catalyst was not possible after 30 h on-stream at 450 ◦C. Filamentous carbon and Ni reduction are considered responsible of the deactivation of the catalyst at 450 ◦C. The analysis of the obtained results suggests that a conjunct polymerization process takes place and is the precursor of the reaction products and the carbon species. However, a detailed study of the mechanism of the ETP-reaction should be done for a better understanding of the deactivation of Ni/AlMCM-41

Direct conversion of ethene to propene on Ni/AlMCM-41 – study of the reaction mechanism

Introduction: Recently, it has been shown that the direct conversion of ethene to propene (ETP-reaction) is an attractive alternative to face the increasing demand of propene [1-3]. In this reaction, it is proposed that propene is producing through a sequence of three single chemical reactions [2]. This sequence consists in the dimerization of ethene to 1-butene in the first step. In the second one, 1-butene dimerizes to 2-butene that reacts with another molecule of ethene to produce propene through a metathesis reaction. More recently, it has been suggested that during the ETP-reaction, propene is participating in other type of reactions [4]. Therefore, in this work a detailed study of the reaction mechanism of the ETP-reaction has been carried out by investigating separately the isomerization of butene isomers, the metathesis of ethene and 2-butene and the retro-metathesis of propene. In situ DRIFTS characterization was also performed. Experimental: The catalysts synthesis procedure is described in [4]. The following experiments were performed; (a) Isomerization of 1-butene, cis-butene, trans-butene by feeding a mixture of 2 vol.% of 1- or cis- or trans-butene with a GHSV of 200 l h-1gcat-1; (b) Metathesis of ethene and 2-butene (trans- or cis-butene) by feeding a mixture of ethene and trans- or cis-butene with a feed concentration of 2.5 vol.% for each olefin, GHSV 1.4 h-1gcat-1; (c) Metathesis of propene was carried out by feeding a mixture of 5 vol.% propene in nitrogen, GHSV 1.4 h-1gcat-1. All experiments were performed in a fixed-bed reactor consisting of a quartz tube with an inner diameter of 0.6 cm at atmospheric pressure. The temperature was changed from 50 to 475 °C. The feed and reaction products were analyzed by on-line CG/MS. In situ DRIFTS was done for ETP-experiments by feeding to a DRIFTS cell a mixture of 2.5% of ethene in nitrogen. The DRIFTS spectra were collected at different temperature without interrupting the ethene feed. Results and short discussion No side reactions were observed in the isomerization of cis- and trans-butene. The contrary was observed in the isomerization of 1-butene. The occurrence of the isomerization of butene confirms the acidity of the catalysts. No catalytic cracking of butene was observed because of the modest acidity of the catalysts. Metathesis of ethene and butenes did not produce propene as main reaction product, indicating that Ni/AlMCM-41 catalysts are not efficient catalysts in metathesis reactions. This behavior was confirmed by feeding propene into the reactor (the retro-metathesis of propene), where the main reaction products were hexenes isomers. The in situ DRIFTS experiments confirmed the formation of oligomeric species on the surface of the catalyst during the ETP-reaction. This type of compounds might be precursor for different carbon species that were observed in the ETP-reaction [4]. The results obtained in this work strongly suggest that a conjunct polymerization (hydropolimerization) is taking place, where propene is one of the main reaction products at high temperature. This conjunct polymerization yields a product that is a complex mixture of saturated (alkanes and cycloalkanes) and unsaturated (alkanes, alkapolyenes, cycloalkenes, and cycloalkapolyenes) hydrocarbons, and occasionally even aromatic compounds [5]. No metathesis properties could be confirmed on Ni/AlMCM-41 catalysts. Detailed results will be discussed during the poster session. References [1] M. Iwamoto, Y. Kosugi, J. Phys. Chem. C., 111 (2006) 13. [2] M. Iwamoto, Catal. Surv. Asia, 12 (2008) 28. [3] T. Lehmann, T. Wolff, V.M. Zahn, P. Veit, C. Hamel, A. Seidel-Morgenstern, Catal. Commun., 12 (2011) 368. [4] L. Alvarado Perea, T. Wolff, P. Veit, L. Hilfert, F. T. Edelmann, C. Hamel, A. Seidel-Morgenstern, J. Catal. 305 (2013) 154. [5]. Olah, G.A.,Á. Molnár, Hydrocarbon Chemistry, 2003