Browsing by Author "Fernandes, Auguste"
Now showing 1 - 10 of 11
Results Per Page
Sort Options
- Aluminum containing dendrimeric silica nanoparticles as promising metallocene catalyst supports for ethylene polymerizationPublication . Cecílio, Duarte M.; Fernandes, Auguste; Lourenço, João P.; Ribeiro, M. RosárioSeveral aluminum containing dendrimeric silica nanospheres, DSAl materials, were prepared using different synthesis and post-synthetic procedures. These materials were used for the immobilization of Cp2ZrCl2 via direct impregnation. The support materials were rigorously characterized by TEM, N2 adsorption, FTIR (using pyridine as probe molecule) and SS-NMR to assess their morphological, textural and surface acidic properties. Supported catalysts were tested in ethylene homopolymerization using methylaluminoxane (MAO) as co-catalyst and scavenger. The relationships between the types and strength of acid sites, as well as the textural and morphological parameters of DSAl materials with the behavior of catalytic systems are explored in this work. The results analyzed in this paper confirm the importance that support surface acidity plays in the formation of the active species for ethylene polymerization and in its activity without neglecting the contribution of support textural properties as well.
- 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.
- Conversion of glycerol over vanadium supported beta zeolite: role of acidity and alkali cationsPublication . Fernandes, Auguste; Ribeiro, M. Filipa; Lourenço, João P.Different vanadium supported beta zeolites modified with Cs and K, were used as catalysts for the conversion of glycerol, in gas phase, without any external reductant. The catalytic data show that all the catalysts studied are active in the conversion of glycerol and that the presence of vanadium oxide species promotes the formation of allyl alcohol. Moreover, modification of the vanadium-based catalysts with Cs or K changes the vanadium species and puts in evidence the importance of the acidity in this process. A low density of acid sites favors the formation of allyl alcohol, in detriment of acrolein one. The data also indicate that the formation of these compounds is closely related and could be explained using the same mechanistic path.
- Gas-phase conversion of glycerol to allyl alcohol over vanadium-supported zeolite betaPublication . Almeida, Ruben; Filipa Ribeiro, M.; Fernandes, Auguste; Lourenço, João PauloVanadium oxide supported beta zeolite (Si/Al = 25, 4% V) was used as catalyst for the one-pass gas-phase conversion of glycerol to allyl alcohol without any external reductant. The catalytic data strongly suggest a consecutive reactions path involving the dehydration to acrolein over the zeolite acid sites followed by a selective reduction through a hydrogen-transfer reaction. Acidity is expected to play a major role in what concerns the selectivity, as demonstrated by the catalytic results obtained by the impregnation of vanadium on a previously Cs-exchanged sample that achieved ca. 30% selectivity to allyl alcohol at ca. 20% glycerol conversion.
- Gas-phase conversion of glycerol to allyl alcohol over vanadium-supported zeolite betaPublication . Almeida, Ruben; Ribeiro, M. Filipa; Fernandes, Auguste; Lourenço, João P.Vanadium oxide supported beta zeolite (Si/Al=25, 4% V) was used as catalyst for the one-pass gas-phase conversion of glycerol to allyl alcohol without any external reductant. The catalytic data strongly suggest a consecutive reactions path involving the dehydration to acrolein over the zeolite acid sites followed by a selective reduction through a hydrogen-transfer reaction. Acidity is expected to play a major role in what concerns the selectivity, as demonstrated by the catalytic results obtained by the impregnation of vanadium on a previously Cs-exchanged sample that achieved ca. 30% selectivity to allyl alcohol at ca. 20% glycerol conversion.
- Gas-phase dehydration of glycerol over hierarchical silicoaluminophosphate SAPO-40Publication . Fernandes, Auguste; Filipa Ribeiro, M.; Lourenço, J. P.Hierarchical silicoaluminophosphate SAPO-40 was synthetized using an organosilane acting as additional porogen agent. The structural, textural and acid properties of the new material were evaluated using XRD, 29Si and 27Al MAS NMR, SEM, N2 adsorption, pyridine adsorption followed by IR spectroscopy and thermal analyses. The evaluation of the catalytic performance in the dehydration of glycerol has evidenced a high activity and a very low deactivation rate. When compared with the conventional SAPO-40, this catalyst shows higher acrolein selectivity and a significantly longer catalytic lifetime.
- A novel approach for preparation of nanocomposites with an excellent rigidity/deformability balance based on reinforced HDPE with halloysitePublication . Cecílio, Duarte M.; Cerrada, Maria L.; Pérez, Ernesto; Fernandes, Auguste; Lourenço, João P.; McKenna, Timothy F. L.; Ribeiro, M. RosárioAn innovative approach, designated as supported activator (SA), allows preparation of high density polyethylene (HDPE)-based highly performant hybrid materials. This procedure makes use of a nano-sized supported methylaluminoxane (MAO)-activator, based on halloysite natural nanotubes (HNT), combined with an in situ supporting concept. The new protocol when compared with a more conventional approach gives rise to higher polymerization activities as well as ultimate materials with better morphological features, greater crystallinity, thicker crystals, and highly increased stiffness. Moreover, a remarkable synergy between rigidity and toughness is attained. The Young’s modulus of a film obtained from the nanocomposite with the highest HNT content increases more than 70 % relatively to a pristine HDPE film, while retaining the limit stretching ability of pristine HDPE (more than 800%). A beneficial impact of using a high aspect ratio support such as HNT in the mechanical properties is also observed, when compared to similar HDPE hybrid materials derived from dendrimer-like silica (DS) nanospheres. Interestingly, polymerization activity, polymer features and derived properties found in the ultimate materials are less impacted by support/filler nature than by preparation method. This fact highlights the crucial role of the synthetic methodology used and corroborates the high potential of the SA route for the preparation of high-performance polyethylene-based nanocomposites with an excellent balance between stiffness and deformability.
- On the characterization and performance of highly dispersed TiO2 nanoparticles onto BEA zeolite in the continuous gas-phase photooxidation of ethylene.Publication . Ferreira, Ricardo; Morales-Torres, Sergio; Pastrana-Martínez, Luisa María; Maldonado Hodar, Francisco Jose; Lourenço, João P.; João, Isabel M.; Silva, João Miguel; Ribeiro, M. Filipa; Fernandes, AugusteTwo series of TiO2-based zeolite composites (BEA structures) were prepared by employing a sol–gel method using two different synthesis approaches, i.e., acidic and basic media. Different photocatalytic composites obtained with increasing amounts of TiO2 (10–50 wt%) were thoroughly characterized and subsequently tested in the photooxidation of ethylene in a continuous gas-phase system. Results showed that sol–gel experimental conditions had a significant effect on the final properties of the samples, as photocatalytic composites obtained under basic conditions showed better TiO2 dispersion and interaction with the BEA support than their counterparts prepared in an acidic medium. The same photocatalysts showed high performance in ethylene photooxidation, demonstrating complete mineralization and results comparable to or even better than those of the bulk TiO2 material.
- Sulfonic-functionalized SBA-15 as an active catalyst for the gas-phase dehydration of glycerolPublication . Lourenço, J. P.; Macedo, Maria I.; Fernandes, AugusteSulfonic-functionalized mesoporous silicas (SBA-15) were used as catalysts in the gas-phase dehydration of glycerol at moderate temperature (275 and 300 ºC). For the tested conditions all the samples show a very high catalytic activity. At the lowest temperature and for 140 h on stream a nearly constant selectivity to acrolein of ca. 80 % could be obtained. Both the pore size and density of acid sites play an important role in the deactivation rate and selectivity: larger pore size may extend significantly the catalytic activity and high density of acid sites may reduce acrolein production. Increasing the temperature to 300 ºC is beneficial to the acrolein production, but it also leads to an increase of the deactivation rate.
- Unique stiffness-deformability features of dendrimeric silica reinforced HDPE nanocomposites obtained by an innovative routePublication . Cecílio, Duarte M.; Cerrada, Maria L.; Pérez, Ernesto; Fernandes, Auguste; Lourenço, João P.; McKenna, Timothy F.L.; Ribeiro, M. RosárioA set of dendrimeric silica (DS) reinforced polyethylene-based nanocomposites is prepared using a novel and straightforward in-situ catalyst supporting procedure by means of "in-situ" polymerization technique, labeled DSSA. These materials are characterized with regard to molar masses, filler dispersion, thermal stability, crystalline characteristics, thermal properties and mechanical response and then compared with an equivalent set of samples prepared using a more common method, named DS-MAO, as well as a non-reinforced HDPE reference. The mechanical performance of all these materials is discussed based on the crystalline features and molar masses of the polymeric component together with the dispersion of the DS nanofiller. The results of this study confirm the potential of the DS-SA approach as an innovative and promising technique, with resulting materials achieving superior filler dispersion and significantly higher mechanical performance compared to their DS-MAO analogues at high filler loadings, while retaining the limit stretching ability of HDPE.