Centro de Química Estrutural

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Bio-oils/FCC co-processing: insights into the adsorption of guaiacol on Y zeolites with distinct acidity and textural properties

Publication . Silva, João; Ribeiro, M. F.; Graça, I.; Fernandes, A.

The guaiacol adsorption capacity of several Y zeolites with different physicochemical properties was tested by performing breakthrough adsorption experiments, in order to investigate the guaiacol adsorption on Fluid Catalytic Cracking catalysts during bio-oils/FCC feedstocks co-processing. X-Ray diffraction, nitrogen sorption measurements and pyridine adsorption followed by Infrared Spectroscopy were used to determine the framework Si/Al ratio, the textural parameters, and finally the nature and amount of acid sites. Klinkenberg model was used to fit the experimental data and to obtain the guaiacol adsorption capacity and ka (overall coefficient of mass transfer) and Ke (adsorption equilibrium constant) parameters, which are directly related to, respectively, kinetic and thermodynamic aspects. Ke values, and so guaiacol adsorption, were observed to increase with the total number of Bronsted and Lewis acid sites on the zeolites, as well as with the amount of Na exchange. Conversely, mesoporosity increases the diffusion rate of guaiacol inside the zeolite structure, leading to higher ka values and decreasing guaiacol retention. Overall, data show that guaiacol adsorption on the FCC catalysts, and so its impact on the activity, might decrease with the catalyst age, owing to the changes on the FCC catalyst properties taking place during operation.

2021-08Journal article

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Ultrasound and radiation-induced catalytic oxidation of 1-phenylethanol to acetophenone with iron-containing particulate catalysts

Publication . Soliman, Mohamed Mostafa Aboelhassan; Kopylovich, Maximilian N.; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Ferraria, Ana Maria; Rego, Ana; Correia, Luís M. M.; Saraiva, Marta S.; Pombeiro, Armando

Iron-containingparticulatecatalystsof0.1–1 µmsizewerepreparedbywetandball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic ﬁeld of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling aﬀord better acetophenone yields (up to 83%). A signiﬁcant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also veriﬁed.

2020-02-01Journal article

Open access

Supercritical carbon dioxide extraction, antioxidant activity, and fatty acid composition of bran oil from rice varieties cultivated in Portugal

Publication . Pinto, Tânia I.; Coelho, Jose; Pires, Bruna I.; Neng, N.R.; Nogueira, José M.; Bordado, João; Sardinha, José P.

Bran of different rice cultivars produced in Portugal were used to study supercritical carbon dioxide extraction conditions of rice bran oil (RBO) and evaluate and compare antioxidant activity and fatty acid composition of the different rice bran varieties. The effect of plant loading (10-20 g), CO2 flow rate (0.5-1.5 L/min), pressure (20-60 MPa), and temperature (40-80 degrees C) was studied. The amount of oil extracted ranged from 11.72%, for Ariete cultivar, to 15.60%, for Sirio cultivar. The main fatty acids components obtained were palmitic (13.37%-16.32%), oleic (44.60%-52.56%), and linoleic (29.90%-38.51%). Excellent parameters of the susceptibility to oxidation of the oils were obtained and compare. RBO of Ariete and Gladio varieties presented superior DPPH and ABTS radical scavenging activities, whereas, Minima, Ellebi, and Sirio varieties had the lowest scavenging activities. Moreover, the oil obtained towards the final stages of extraction presented increased antioxidant activity.

2021-08-05Journal article

Open access

Friedel-crafts acylation reaction over hierarchical Y zeolite modified through surfactant mediated technology

Publication . Martins, Angela; Neves, Vera; Moutinho, João; Nunes, Nelson; Carvalho, Ana

Friedel-Crafts acylation reaction was studied under mild conditions using hierarchical HY zeolite samples prepared through surfactant mediated technology, in the presence of NH4OH, using CTAB or DTAB as surfactants and changing the duration of treatment from 6 to 48 h. The materials were characterized by powder X-ray diffraction, low temperature N2 adsorption isotherms, SEM microscopy and pyridine adsorption followed by FTIR. The catalytic behaviour was studied in the acylation of furan by acetic anhydride. The catalytic results reflect the role of the duration of the treatment as well as the surfactant molecule used. As the time of treatment increases, the enlargement of the pores leads to an increase of the rate constant and turnover frequency (TOF), except for sample modified during longer time, 48 h, due to the occurrence of secondary reactions that produce larger products or reaction intermediates that become trapped inside the pores. The role of the surfactant molecule is also relevant since the sample modified in the presence of the larger surfactant molecule, CTAB, a significant increase in product yield and rate constant is obtained when compared with the sample prepared in the same conditions using DTAB. However, in that case, by prolonging the treatment a substantial decrease in the same parameters occurs due to the occurrence of deactivation phenomena, pointing out that the optimized modification of porosity needs to be customized according to the needs of each catalytic system.

2021-08Journal article

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Silver(I) coordination polymers immobilized into biopolymer films for antimicrobial applications

Publication . Fernandes, Tiago; Costa, Inês F. M.; Jorge, Paula; Sousa, Ana Catarina; André, Vânia; Cerca, N.; Kirillov, Alexander M.

This study describes a template-mediated self-assembly synthesis, full characterization, and structural features of two new silver-based bioactive coordination polymers (CPs) and their immobilization into acrylated epoxidized soybean oil (ESOA) biopolymer films for antimicrobial applications. The 3D silver(I) CPs [Ag-4(mu(8)-H(2)pma)(2)](n)center dot 4nH(2)O (1) and [Ag-5(mu(6)-H(0.5)tma)(2)(H2O)(4)] (n)center dot 2nH(2)O (2) were generated from AgNO3 and pyromellitic (H(4)pma) or trimesic (H(3)tma) acid, also using N,N'-dimethylethanolamine (Hdmea) as a template. Both 1 and 2 feature the intricate 3D layer-pillared structures driven by distinct polycarboxylate blocks. Topological analysis revealed binodal nets with the flu and tcj/hc topology in 1 and 2, respectively. These CPs were used for fabricating new hybrid materials, namely, by doping the [ESOA](n) biopolymer films with very low amounts of 1 and 2 (0.05, 0.1, and 0.5%). Their antimicrobial activity and ability to impair bacterial biofilm formation were investigated in detail against both Gram-positive (Staphylococcus epidermidis and Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria. Both silver(I) CPs and derived biopolymer films showed activity against all the tested bacteria in a concentration-dependent manner. Compound 1 exhibited a more pronounced activity, especially in preventing biofilm growth, with mean bacterial load reductions ranging from 3.7 to 4.3 log against the four bacteria (99.99% bacterial eradication). The present work thus opens up antibiofilm applications of CP-doped biopolymers, providing new perspectives and very promising results for the design of functional biomaterials.

2021-03-24Journal article

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