Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 1. Effect of nickel loading and preparation conditions on catalyst properties

Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, Ni/HZSM-5 catalysts were synthesized via deposition-precipitation (DP) and characterized. The effect of synthesis parameters; including nickel loading, DP time (synthesis contact time), and calcination temperature, on catalyst properties were studied. N2 and CO2 adsorption techniques were used to look at textural properties and confirmed the existence of lamellar species generated from DP. X-ray diffraction (XRD) confirmed that nickel metal was present on the support after reduction and passivation of the catalyst. Temperature programmed reduction showed that all the catalyst preparations were reducible at 733 K after 4 h, and that the DP method formed a mixture of Ni2+ species on the support. Transmission electron microscopy, XRD, and H2 chemisorption were used to determine approximate particle size and dispersion of nickel metal. From all the preparations, the 15 wt% Ni/HZSM-5 catalyst with long DP time (16 h) and low calcination temperature (673 K), exhibited the most favorable particle size (~5 nm) and dispersion (7%)

Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 2. Catalytic hydrodeoxygenation reactions of lignin model compounds in organic and aqueous systems

Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, the ability of catalysts prepared via deposition-precipitation (DP) to perform hydrodeoxygenation (HDO) on two lignin model compounds in organic and aqueous solvents was evaluated; guaiacol in dodecane and 2-phenoxy-1-phenylethanol (PPE) in aqueous solutions. All Ni/HZSM-5 catalysts were capable of guaiacol HDO into cyclohexane at 523 K. The role of the HZSM-5 acid sites was confirmed by comparison with Ni/SiO2 (inert support) which exhibited incomplete deoxygenation of guaiacol due to the inability to perform the cyclohexanol dehydration step. The catalyst prepared with 15 wt% Ni, a DP time of 16 h, and a calcination temperature of 673 K (Ni(15)/HZSM-5 DP16_Cal673), performed the guaiacol conversion with the greatest selectivity towards HDO products, with an intrinsic rate ratio (HDO rate to conversion rate) of 0.31, and 90% selectivity to cyclohexane. Catalytic activity and selectivity of Ni/HZSM-5 (15 wt%) in aqueous environments (water and 0.1 M NaOH solution) was confirmed using PPE reactions at 523 K. After 30 min reaction time in water, Ni/HZSM-5 exhibited ~100% conversion of PPE, and good yield of the desired products; ethylbenzene and phenol (~35% and 23% of initial carbon, respectively). Ni/HZSM-5 in NaOH solution resulted in significantly higher ring saturation compared to the Ni/HZSM-5 in water or the NaOH solution control

Massive open star clusters using the VVV survey III: A young massive cluster at the far edge of the Galactic bar

Context: Young massive clusters are key to map the Milky Way's structure, and near-IR large area sky surveys have contributed strongly to the discovery of new obscured massive stellar clusters. Aims: We present the third article in a series of papers focused on young and massive clusters discovered in the VVV survey. This article is dedicated to the physical characterization of VVV CL086, using part of its OB-stellar population. Methods: We physically characterized the cluster using $JHK_S$ near-infrared photometry from ESO public survey VVV images, using the VVV-SkZ pipeline, and near-infrared $K$-band spectroscopy, following the methodology presented in the first article of the series. Results: Individual distances for two observed stars indicate that the cluster is located at the far edge of the Galactic bar. These stars, which are probable cluster members from the statistically field-star decontaminated CMD, have spectral types between O9 and B0V. According to our analysis, this young cluster ($1.0$ Myr $<$ age $< 5.0$ Myr) is located at a distance of $11^{+5}_{-6}$ kpc, and we estimate a lower limit for the cluster total mass of $(2.8^{+1.6}_{-1.4})\cdot10^3 {M}_{\odot}$. It is likely that the cluster contains even earlier and more massive stars.Comment: Accepted for publication as a Letter in A&

Spatio-temporal variation in the composition of the macroalgae assemblage of the intertidal rocky zone from maitencillo, valparaíso, central coast of Chile

Indexación: Scopus.Records on the diversity of algae serve as a foundation for establishing management and environmental protection programs, as well as for determining new commercial uses of algae. With this context in mind, the goal of the present study was to determine the richness, coverage, and composition of the macroalgae assemblage in the intertidal zone of Maitencillo, Valparaíso, Chile over the course of 3 years (2013-2015). A total of 29 species were recorded from 3 phyla - 23 Rhodophyta; 3 Ochrophyta, of the Phaeophyceae class; and 3 Chlorophyta. Species richness presented high spatial and temporal variations, with these variations most significantly explained by intertidal zone (61%) and the seasons (31%). The highest levels of specific richness were recorded in the mid and lower intertidal zones (14 species) in spring, as well as in the lower intertidal zone (14 species) during summer. The lowest values of specific richness were recorded for the mid intertidal zone (2 species) during fall. The distinct levels of the intertidal zone also notably impacted algae assemblage, explaining 53% of variation while the seasons explained 18% of variation. The greatest coverage was recorded in the mid intertidal zone during spring, with a predominance of Mazzaella laminarioides and Ulva spp. complex. In turn, the lowest coverage was found in fall, linked with processes of sand accretion. In rocky walls, the Pyropia complex dominated. Results indicate a marked pattern of vertical and seasonal distribution in the macroalgae assemblage, as well as notably high presence of Rhodophyta species. This benthic flora description serves to update information on the diversity of representative algal species from Valparaíso Region of Chile. © 2018, Universidad de Valparaiso. All rights reserved

Dynamic heterogeneities in attractive colloids

We study the formation of a colloidal gel by means of Molecular Dynamics simulations of a model for colloidal suspensions. A slowing down with gel-like features is observed at low temperatures and low volume fractions, due to the formation of persistent structures. We show that at low volume fraction the dynamic susceptibility, which describes dynamic heterogeneities, exhibits a large plateau, dominated by clusters of long living bonds. At higher volume fraction, where the effect of the crowding of the particles starts to be present, it crosses over towards a regime characterized by a peak. We introduce a suitable mean cluster size of clusters of monomers connected by "persistent" bonds which well describes the dynamic susceptibility.Comment: 4 pages, 4 figure

Effect of morphology and hydrophobization of MoS2 microparticles on the stability of poly-α-olefins lubricants

International audienceThe use of MoS ⁠ 2 nanoparticles as additive to lubricating oils is restricted by their low stability in oily media, which limits their use despite the enormous benefits associated with their intrinsic properties in terms of reduction of friction and wear coefficients. In this context, we investigated the effect of morphologies (platelets vs spheres) and surface functionalization of nanoparticles on the stability of their suspensions in poly-α-olefins (PAO) with various viscosities, which are base oils used in wind turbines. The particles were characterized by XRD, FTIR, scanning electron microscopy, atomic force microscopy and dynamic light scattering, and the stability of the resultant formulations was followed by optical (non-contact) measurements. It was found that the dispersions had similar stability despite the larger size of platelet-like particles compared to spherical ones (1-5 μm vs 600-800 nm). The dispersibility could be increased through grafting of alkylsilane on the surface defects (the longer the alkyl chain, the more stable the formulation) and with the increase of the oil kinematic viscosity (from 34 to 1705 cps at 25 °C)

New galactic star clusters discovered in the VVV survey : Candidates projected on the inner disk and bulge

Context. VISTA Variables in the Vía Láctea (VVV) is one of six ESO Public Surveys using the 4 meter Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey covers the Milky Way bulge and an adjacent section of the disk, and one of the principal objectives is to search for new star clusters within previously unreachable obscured parts of the Galaxy. Aims. The primary motivation behind this work is to discover and analyze obscured star clusters in the direction of the inner Galactic disk and bulge. Methods. Regions of the inner disk and bulge covered by the VVV survey were visually inspected using composite JHKS color images to select new cluster candidates on the basis of apparent overdensities. DR1, DR2, CASU, and point spread function photometry of 10 × 10 arcmin fields centered on each candidate cluster were used to construct color-magnitude and color-color diagrams. Follow-up spectroscopy of the brightest members of several cluster candidates was obtained in order to clarify their nature. Results. We report the discovery of 58 new infrared cluster candidates. Fundamental parameters such as age, distance, and metallicity were determined for 20 of the most populous clusters.Peer reviewedFinal Accepted Versio