Browsing by Author "Lourenço, J. P."
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- An elegant way to increase acidity in SAPOs: use of methylamine as co-template during synthesisPublication . Fernandes, Auguste; Ribeiro, F. R.; Lourenço, J. P.; Gabelica, Z.SAPO-34 and SAPO-11 with an increased number of acid sites were synthesized by adding methylamine (MA) as co-template to tetraethylammonium hydroxide (TEAOH) or dipropylamine (DPA) respectively used as true templates.
- Biodegradable polyesters reinforced with mesoporous silica particlesPublication . Campos, João M.; Ribeiro, M. R.; Deffieux, A.; Péruch, F.; Lourenço, J. P.; Cerrada, María L.In recent years, the development of mechanically reinforced nanocomposites based on biodegradable polyester matrices has gained a strong incentive due to their potential use as biomaterials and to growing worldwide environmental concerns.
- Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0) as precursor to a molybdenum(VI) catalyst for olefin epoxidationPublication . Figueiredo, Sónia; Gomes, Ana C.; Fernandes, José A.; Paz, Filipe A. Almeida; Lopes, Andre D.; Lourenço, J. P.; Pillinger, Martyn; Gonçalves, Isabel S.Bis(pyrazolyl)methanetetracarbonyl-molybdenum(0), cis-[Mo(CO)4(BPM)] (1), was prepared from Mo(CO)6 and the ligand bis(pyrazolyl)methane (BPM), and examined as a catalyst precursor for the epoxidation of olefins using tert-butylhydroperoxide (TBHP) as oxidant. Catalytic activities followed the sequence 1-octene < trans-2-octene < a-pinene < (R)-(þ)-limonene < cis-cyclooctene, and, with the exception of a-pinene and limonene, the corresponding epoxide was always the only reaction product. Turnover frequencies for the epoxidation of cyclooctene were 580 mol molMo 1 h 1 at 55 C and 1175 mol molMo 1 h 1 at 75 C, which compare favourably with those found for other molybdenum carbonyl complexes used as catalyst precursors for the same reaction under similar conditions. Catalytic activities were lower in the presence of organic co-solvents, decreasing in the sequence 1,2-dichloroethane > nitromethane > ethanol > hexane > acetonitrile. It is proposed that the oxodiperoxo complex [MoO(O2)2(BPM)] (2) may be the active catalyst formed in situ by oxidative decarbonylation of 1, since crystals of 2 suitable for structure determination by X-ray diffraction were obtained from the reaction solution recovered after a catalytic run at 55 C with cis-cyclooctene as substrate. In support of this hypothesis, the catalytic performance of 2 for the epoxidation of cyclooctene at 55 C is very similar to that for 1.
- Characterization of stability and porosity of SAPO-40 using m-xylene as model reactionPublication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.The thermal and hydrothermal stability of SAPO-40 has been evaluated using the isomerization of m-xylene as model reaction. The characterization of the porosity was also studied and compared to other well known structures, namely Y zeolite, mordenite and ZSM-5. The structural changes that occur under thermal treatments influence the activity and selectivity of SAPO-40, while hydrothermal treatments do not significantly change those properties. The results confirm the high stability of SAPO-40 under thermal and hydrothermal treatments. Catalytic tests and adsorption of cyclohexane indicate that regular large side pockets or lobes exist along the main channels of SAPO-40, which create a large void volume responsible for the high rate of adsorption, high amount of adsorbed cyclohexane and the low shape selectivity in m-xylene isomerization.
- Charged pullulan derivatives for the development of nanocarriers by polyelectrolyte complexationPublication . Dionísio, Marita; Braz, L.; Corvo, M.; Lourenço, J. P.; Grenha, Ana; Costa, Ana M. Rosa daPullulan, a neutral polysaccharide, was chemically modified in order to obtain two charged derivatives: reaction with SO3(.)DMF complex afforded a sulfate derivative (SP), while reaction with glycidyltrimethylammonium chloride gave a quaternary ammonium salt (AP). The presence of the charged groups was confirmed by FTIR. Assessment of the positions where the reaction took place was based on (1)H- and (13)C NMR (COSY, HSQC-TOCSY, HSQC-DEPT, and HMBC) experiments. Estimation of the degree of substitution (DS) was made from elemental analysis data, and further confirmed by NMR peak areas in the case of AP. These new derivatives showed the capability to condense with each other, forming nanoparticles with the ability to associate a model protein (BSA) and displaying adequate size for drug delivery applications, therefore making them good candidates for the production of pullulan-based nanocarriers by polyelectrolyte complexation.
- Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41Publication . Monteiro, Bernardo; Balula, Salete S.; Gago, Sandra; Grosso, Carla; Figueiredo, Sónia; Lopes, Andre D.; Valente, Anabela A.; Pillinger, Martyn; Lourenço, J. P.; Gonçalves, Isabel S.A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17Mo/nm2 was prepared by liquid phase deposition ofMoO2Cl2(dmf)2 (1) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N2 adsorption studies of Mo-MCM-41 indicate that the texture properties of the support were preserved during the grafting experiment. On the basis of evidence from FTIR spectroscopy, 13C and 29Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO2[(–O)3SiO]2(dmf)2} species, with a small contribution from oxo-bridged dimers. Catalysis tests show that complex 1 and Mo-MCM-41 are highly active oxidation catalysts for liquid-phase epoxidation of unfunctionalised olefins using tert-butylhydroperoxide as oxidant, from ambient to 55 ◦C. The high stability and recyclability of the heterogeneous Mo-MCM-41 catalyst is attributed to the strong metal oxide–support interaction. With cyclooctene, 1-octene, trans-2-octene and norbornene substrates, the corresponding epoxides were the only observed reaction products. The reactions of the other substrates gave by-products such as 8,9-p-menthen-1,2-diol from (R)-(+)-limonene, campholenic aldehyde from -pinene, and benzaldehyde from styrene. The addition of dichloromethane as a co-solvent had a beneficial effect on catalytic performance, and in the case of (R)-(+)-limonene allowed the epoxide to be formed as the only reaction product.
- Copolymerization of ethylene and non-conjugated diene with metallocene/methylaluminoxane system supported on MCM-41 mesoporous materialPublication . Lopes, D. E. B.; Marques, M. F. V.; Dias, M. L.; Ribeiro, M. R.; Lourenço, J. P.Ethylene was copolymerized with the non-conjugated diene 5,7-dimethylocta-1,6-diene by metallocene catalysts, homogenous and supported on MCM-41 mesoporous material activated by methylaluminoxane at room temperature. The employed metallocenes were (BzCp)2ZrCl2 (1), (C18H37Cp)2ZrCl2 (2), (CH3)2Si(Ind)2ZrCl2 (3) and /2C(Cp,Flu)ZrCl2 (4). Diene incorporation and thermal characteristic of the polymers were determined by 13CNMR and DSC. For the homogeneous systems, only the unbridged metallocene (1) showed a decrease in the activity as the diene content was increased. The ability for diene incorporation in the polymer chain followed the catalyst order (1) < (3) < (2) < (4). Regarding the supported systems, it was observed that all of them showed lower activity than the corresponding homogeneous catalysts. A sharp loss of activity in relation to the homogeneous counterpart was noticed by employing the ansa-metallocenes on MCM-41, especially the complex (4) supported catalyst. The effect of the mesoporous material as support on the behavior of the studied metallocene homogeneous systems in ethylene–diene copolymerization was an increase of polymer molecular weight, maintaining the same level of diene incorporation, except for catalyst (2), when a decrease of the diene incorporation was observed.
- Cycloaddition reactions of nitrosoalkenes, azoalkenes and nitrile oxides mediated by hydrotalcitePublication . Lemos, A.; Lourenço, J. P.Mg:Al 3:1 hydrotalcite (Ht), used in catalytic quantities, promotes the generation of nitrosoalkenes, azoalkenes and nitrile oxides. These can be intercepted in situ by heterocycles and olefins in [4+2] and [3+2] cycloaddition reactions, producing dihydro-1,2-oxazines, tetrahydropyridazines and isoxazolines. The regeneration and reuse of Ht without loss of activity and the absence of organic solvent are the main advantages of this methodology.
- Decorated MCM-41/polyethylene hybrids: crystalline details and viscoelastic behaviorPublication . Cerrada, María L.; Pérez, Ernesto; Lourenço, J. P.; Bento, A.; Ribeiro, M. R.Polyethylene-based nanocomposites have been prepared by in-situ polymerization of ethylene with mesostructured MCM-41. Different approaches are used to improve interfacial adhesion between components, high density polyethylene (HDPE) matrix and MCM-41. These consist either of the incorporation of UA in the polymer chains by copolymerization in a very small content or of the modification of MCM-41 surface with the system based on undecenoic acid, UA/triisobutylaluminum, TIBA, before polymerization. The materials attained exhibit minimal changes in the crystallinity resulting from first melting process although a slight increase of long spacing at room temperature is seen as MCM-41 is incorporated in the hybrids. Moreover, a confinement effect is noticed and, thus, a delay in the crystallization process of the macrochains within pores and channels is detected. These novel self-reinforced nanocomposites show higher stiffness than other similar hybrids with poorer interfacial adhesion. Accordingly, they exhibit an enhancement in their mechanical performance without changing the final processing temperature since Tm is the same for all of the specimens.
- Dichlorodioxomolybdenum(VI) complexes bearing oxygen-donor ligands as olefin epoxidation catalystsPublication . Oliveira, Tânia S. M.; Gomes, Ana C.; Lopes, Andre D.; Lourenço, J. P.; Almeida Paz, Filipe A.; Pillinger, Martyn; Gonçalves, Isabel S.Treatment of the solvent adduct [MoO2Cl2(THF)2] with either 2 equivalents of N,N-dimethylbenzamide (DMB) or 1 equivalent of N,N'-diethyloxamide (DEO) gave the dioxomolybdenum(vi) complexes [MoO2Cl2(DMB)2] () and [MoO2Cl2(DEO)] (). The molecular structures of and were determined by single-crystal X-ray diffraction. Both complexes present a distorted octahedral geometry and adopt the cis-oxo, trans-Cl, cis-L configuration typical of complexes of the type [MoO2X2(L)n], with either the monodentate DMB or bidentate DEO oxygen-donor ligands occupying the equatorial positions trans to the oxo groups. The complexes were applied as homogeneous catalysts for the epoxidation of olefins, namely cis-cyclooctene (Cy), 1-octene, trans-2-octene, α-pinene and (R)-(+)-limonene, using tert-butylhydroperoxide (TBHP) as oxidant. In the epoxidation of Cy at 55 °C, the desired epoxide was the only product and turnover frequencies in the range of ca. 3150-3200 mol molMo(-1) h(-1) could be reached. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the cosolvent. Complexes and were also applied in liquid-liquid biphasic catalytic epoxidation reactions by using an ionic liquid of the type [C4mim][X] (C4mim = 1-n-butyl-3-methylimidazolium; X = NTf2, BF4 or PF6] as a solvent to immobilise the metal catalysts. Recycling for multiple catalytic runs was achieved without loss of activity.