HDS of 4,6-dimethyldibenzothiophene over CoMoS supported mesoporous SiO2-TiO2 materials

TiO2 supported SBA-15 (xTi@SBA-15) materials with various high TiO2 loadings (x = 25, 50 and 70 wt%) have been used as support for impregnation of CoMo active phase for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (46DMDBT) as model molecule representative of gazole cuts. Compared to CoMoS supported over pure commercial TiO2 and conventional Al2O3, a higher total activity was measured corresponding to the presence of isomerization and dismutation reactions due to Brönsted acidity of TiO2. However, the HDS activity remains higher using alumina as support. Moreover, the DDS pathway was found favored to the HYD one with sulfided CoMo supported over xTi@SBA-15 catalysts contrary with alumina as support

Influence of the water vapor on the activity of CuO/SBA-15 SOx adsorbents

Both the performance and regenerability of SO2 adsorbents made of CuO supported on SBA-15 ordered mesoporous silica were studied for a cyclic DeSOx process under wet and dry conditions. H2O vapor decreases the performance of a 16 wt% loading CuO/SBA-15 (16CuO/SBA-15) adsorbent along the adsorption/regeneration cycles performed at 400 °C. Indeed, the SO2 breakthrough adsorption capacity of this adsorbent after ten adsorption- regeneration cycles under wet conditions (5 vol% of H2O) decreases of 61% compared to the SO2 performance obtained under dry conditions. The impact of the temperature as well as the CuO loading on the performance and regenerability of CuO/SBA-15 sorbents were also investigated under dry and wet conditions. XRD, TEM/EDX, N2 physisorption characterizations of the adsorbents were performed after the last cycle to correlate the structural and textural properties of the adsorbents and therefore the copper species, with the performance of the adsorbents. Increasing the temperature up to 450 °C with or without water increases the SO2 adsorption capacity of the 16CuO/SBA-15 adsorbent with higher SO2 adsorption capacity at 450 °C with water than without water. In the presence of water vapor, the 8CuO/SBA-15 adsorbent presents the highest average loss of SO2 adsorption capacity at the breakthrough of around 71% when expressed in mgSO2/gCuO , compared to the ones obtained with the 16CuO/SBA-15 and the 26CuO/SBA-15 adsorbents. The increase of the CuO loading up to 26 wt%, shows that the contribution of the surface copper active phase highlighted by the desorption curves, decreases significantly for the highest CuO loading under wet conditions. Moreover, with or without water, the highest total SO2 adsorption capacities obtained after the tenth cycle are observed for the lowest CuO loading (8 wt% of CuO: 547 and 495 mgSO2/gCuO without and with H2O, respectively). These higher total SO2 adsorption capacities could be explained by a better CuO phase dispersion on the SBA-15 support, which makes the copper active species more reactive especially with H2O

Structure-Thermal Conductivity Tentative Correlation for Hybrid Aerogels Based on Nanofibrillated Cellulose-Mesoporous Silica Nanocomposite

Hybrid aerogels have been prepared by freeze-drying technique after mixing water dispersions of cellulose microfibers or cellulose nanofibers and silica (SiO2) of type SBA-15 (2D-hexagonal). The prepared composites were characterized by different analysis techniques such as SEM, hot-filament, DMA, etc. These composites are compared to those previously prepared using nanozeolites (NZs) as mineral charge. The morphology studied by SEM indicated that both systems have different structures, i.e., individual fibers for cellulose microfibers WP-based aerogels and films for nanofibrillated cellulose NFC-based ones.... These differences seem to be driven by the charge of the particles, their aspect ratio and concentrations. These hybrid materials exhibit tunable thermal conductivity and mechanical properties. The thermal conductivity values range between ~18 to 28 mW. m–1. K–1and confirm the superinsulation ability of these fibrous aerogels. Synergism on the thermal insulation properties and mechanical properties was shown by adjunction of mineral particles to both cellulose-based aerogels by reaching pore size lower than 100 nm. It significantly reduces the thermal conductivity of the hybrid aerogels as predicted by Knudsen et al. Furthermore, the addition of mineral fillers to aerogels based on cellulose microfibers induced a significant increase in stiffness

Stoichiometric molecular single source precursors to cobalt phosphides

Crystalline cobalt phosphides were synthesized by using three different, low oxidation-state organometallic clusters as precursors, [Co-4(CO)(10)(mu-dppa)], [Co-4(CO)(10)(mu(4)-PPh)(2)] and [Co-4(CO)(8)(mu-dppa)(2)] (dppa = Ph2PNHPPh2), which are characterized by Co/P ratios of 2:1, 2:1 and 1:1, respectively. Depending on their Co/P ratio, these clusters are suitable single-source precursors to form CoP and Co2P without the need to add any other reagent or surfactant. The thermal behavior of these three clusters was investigated under different conditions. The results show how their Co/P ratios, the nature of the atmosphere used for their thermal activation and the temperature control the nature and composition of the resulting phases. (C) 2013 Elsevier B.V. All rights reserved

Deep hydrodesulfurization of 4,6-dimethydibenzothiophene over CoMoS/TiO2 catalysts: Impact of the TiO2 treatment

Mesostructured titania as support for the CoMoS active phase in deep hydrodesulfurization (HDS) of 4,6-dimethydibenzothiophene (4,6-DMDBT) leads to an increase of the intrinsic HDS activity and a higher selectivity for direct desulfurization (DDS) for HDS reaction in contrast with the conventional CoMoS/alumina catalyst. The temperature treatment of the mesostructured TiO2 support, modifies the catalyst’s activity for the transformation of 4,6-DMDBT. The higher total and HDS activities were obtained after treatment at 380 °C corresponding to the higher specific surface area and to a mesostructured TiO2 material with a semi-crystalline anatase framework. Beyond 550 °C, the specific surface area decreases strongly corresponding to a complete crystallization of the mesopores walls into anatase structure. Moreover, the temperature under which the support is treated prior its impregnation has no impact on the selectivity of the transformation routes of the sulfur compound

Characterization of cobalt phosphide nanoparticles derived from molecular clusters in mesoporous silica

The synthesis of well dispersed cobalt phosphide nanoparticles (NPs) in SBA-15 mesoporous silica by wet impregnation of the molecular cluster [Co4(CO)10(μ-dppa)] (1) (dppa = HN(PPh2)2) is described. The thermal activation of the silica impregnated precursor under a H2/N2 (5/95 %) stream at different temperatures to form NPs was studied and it was found that the size of the latter is limited in the 5.5–6.5 nm range by the size of the pores. The obtained materials were characterized by various analytical methods. The porosity and the structure of the mesoporous silica supports were analyzed by N2 adsorption/desorption and small-angle X-ray diffraction. The nanoparticles were characterized by wide-angle X-ray diffraction, transmission electron microscopy in conventional and scanning modes, electron tomography, energy-dispersive X-ray spectroscopy, and magnetic measurements. Cobalt phosphide NPs of few nanometers were observed in the pores of SBA-15

Rapid synthesis of nanostructured porous silicon carbide from biogenic silica

International audienceNanostructured silicon carbide (SiC) is an exceptional material with numerous applications e.g. in catalysis, biomedicine, high performance composites, and sensing. In this study, a fast and scalable method of producing nanostructured SiC from plant materials by magnesiothermic reduction via self-propagating high-temperature synthesis (SHS) route was developed. The produced biogenic material possessed a high surface area above 200 m 2 /g with a SiC crystallite size below 10 nm, which has not been done previously by SHS. This method enables affordable synthesis of the material plant-based precursors in a reaction that only takes a few seconds, thereby paving a way for nanostructured silicon carbide production in high volumes using renewable resources. The material was also functionalized with carboxylic acid and bisphosphonate moieties, and its use as metal adsorbent in applications such as wastewater remediation was demonstrated