Loading...
5 results
Search Results
Now showing 1 - 5 of 5
- Acid-modified clays as green catalysts for the hydrolysis of hemicellulosic oligosaccharidesPublication . Vilcocq, Léa; Spínola, Vítor; Moniz, Patrícia; Duarte, Luís C.; Carvalheiro, Florbela; Fernandes, César; Castilho, PaulaThe hydrolysis of hemicellulosic oligosaccharides (OS) was investigated using acid-activated clays (prepared from natural Porto Santo montmorillonite clay) as catalysts. Acid activation was performed in HCl solution or with aluminium exchange. The clay catalysts were characterized by XRD, N2 adsorption isotherms, CEC, FTIR, titration of acid sites in water and adsorption of sugars and disaccharides. They were tested for the hydrolysis of a model compound, maltose, and of OS-rich liquor from rice straw fractionation. The HCl-activated clays were the most efficient catalysts for maltose hydrolysis. It was demonstrated that the hydrolysis of OS into monomer sugars over a clay catalyst is technically feasible and that this reaction leads to the selective removal of glucose, arabinose and acetic acid side groups from the OS structure, thus yielding simpler xylo-oligosaccharide chains. Furthermore, no significant conversion of monomer sugars into furans was observed.
- Porosity in ion-exchanged and acid activated clays evaluated using n-nonane pre-adsorptionPublication . Ribeiro Carrott, M.M.L.; Cansado, I.P.P.; Carrott, P.J.M.; Russo, P.A.; Castilho, P.; Fernandes, C.; Catrinescu, C.; Breen, C.The applicability of the n-nonane pre-adsorption method for characterising the porosity in clays is presented. Na-SD, a Naþ-exchanged purified bentonite, and materials obtained by Al3þ-exchange and acid treatments of Na-SD and SAz-1 were used. Nitrogen adsorption isotherms, at 196 C, were determined before and after n-nonane pre-adsorption on each of the samples. In all materials, n-nonane remained adsorbed in ultramicropores after outgassing at 25 C. Outgassing at higher temperatures (50, 75 and 200 C) removed nonane and ultramicropores became available for nitrogen adsorption. All treatments on Na-SD led to increase in micropore volume. Larger ultramicropore and supermicropore volumes were obtained for Na-SD acid activated with HCl at 95 C than for treatments at 25 C with HCl or following Al3þ-exchange (Al-SD), and increased with increasing acid concentration to 3 M. Activation with 4 M HCl led to the largest pore volume with contribution from mesopores. However, the specific external surface area was the same as that obtained for Na-SD, Al-SD and for most of the other acid activated samples. Treatments at 95 C with 1 M and 6 M HCl promoted increase in specific external surface area. The micropore volumes and specific external surface area for SAz-1 treated with 1 M HCl at 95 C were larger than those of Al-SAz-1, but lower than those obtained for corresponding materials derived from Na-SD. The n-nonane pre-adsorption method enabled micropore volumes and specific external surface areas to be obtained for all samples.
- Selective methoxylation of limonene over ion-exchanged and acid-activated claysPublication . Catrinescu, C.; Fernandes, C.; Castilho, P.; Breen, C.; Carrott, M.M.L. Ribeiro; Cansado, I.P.P.In this study, we report the use of clay-based catalysts in the methoxylation of limonene, for the selective synthesis of -terpinyl methyl ether. Na-SAz-1, Ca-SWy-2 and Sap-Ca source clays and a montmorillonite (SD) from Porto Santo,Madeira Archipelago, Portugal weremodified by (i) ion-exchange with Al, Fe, Ni and Na and (ii) acid activation, to produce catalysts with markedly different acidic and textural properties. The lack of activity of Ni2+-SAz-1 (with Lewis acidity maximized), provided evidence that the process occurs preferentially on Brönsted acid sites. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150 ◦C, afforded the highest number of Brønsted acid sites located in the clay gallery and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize limonene conversion and selectivity, was studied over Al-SAz-1. When the reaction was performed for 20 h at 40◦ C, the conversion reached 71% with 91% selectivity to the mono-ether. Mild acid activation (1 M HCl, 30 min, reflux) of the raw SAz-1 clay leads to a material with a good catalytic behaviour (slightly inferior to Al-SAz-1), while any increase in the severity of the acid-treatment (6 M HCl, 30 min, reflux), caused a marked decrease in catalytic activity.
- Selective methoxylation of α-pinene to α-terpinyl methyl ether over Al3+ ion-exchanged claysPublication . Catrinescu, C.; Fernandes, C.; Castilho, P.; Breen, C.In this study, we report the use of clay-based catalysts in the methoxylation of -pinene, for the selective synthesis of -terpinyl methyl ether, TME. The main reaction products and intermediates were identified by GC–MS. The reaction conditions (stirring rate and catalystload)that afford a kinetic regime were estab lished. SAz-1 (Cheto, Arizona, USA) source clay and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal, were modified by ion-exchange with Al3+ to produce catalysts with markedly different acidities and textural properties. The catalysts based on the high layer-charge SAz-1 montmo rillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150 ◦C, afforded the highest number of Brønsted acid sites – a significant proportion of which were located in the clay gallery – and this coincided with the maximum catalytic activity. The influence of various reac tion conditions, to maximize -pinene conversion and selectivity, was studied over AlSAz-1. When the reaction was performed for 1 h at 60 ◦C, the conversion reached 65% with 65% selectivity towards the mono-ether, TME. Similar conversions and selectivities required up to 50 h over zeolites and other solid acid catalysts. The kinetic dependencies of this reaction on temperature and reagent concentration, over the selected clays were also investigated. It was established that, in the temperature and reagent con centration regime studied, the reaction was first order with respect to -pinene. The apparent activation energies over the two catalysts, calculated from Arrhenius plots, were almost identical at 72 kJ mol−1.
- Calcium phosphate-mediated gene delivery using simulated body fluid (SBF)Publication . Nouri, Alireza; Castro, Rita; Santos, José L.; Fernandes, César; Rodrigues, João; Tomás, HelenaThe present study aimed at developing a new approach in gene delivery of calcium phosphate nanoparticles through simulated body fluid (CaP-SBF). The physicochemical and biological characteristics of the CaP-SBF nanoparticles were compared with those made in pure water (CaP-water) via a similar procedure. The CaP-SBF and CaP-water solutions were then adjusted to two different pH values of 7.4 and 8.0, mixed with plasmid DNA (pDNA), and added in varying amounts to human embryonic kidney (HEK 293T) cells. The transfection efficiency and cell viability were studied in vitro by reporter gene (luciferase and Enhanced Green Fluorescent Protein) expression and the resazurin reduction assay, respectively, 24 and 48 h after the incubation with the nanoparticles. Our results indicated considerably high in vitro transfection efficiency for CaP-SBF/DNA complexes at physiological pH (7.4) with high amounts of CaP. Additionally, the SBF solution exhibited the ability to reduce the rapid growth of CaP particles over time, leading to higher transfection efficiency of CaP-SBF/DNA complexes than those made in water (CaP-water/DNA).