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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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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From manganese oxide to manganese sulphide: Synthesis and its effect on electrochemical energy storage performance

Publication . Almeida, M. M.; Más, A. A.; Moura E Silva, Teresa; MONTEMOR, M.F

High power pseudocapacitors are extremely relevant to answer specific needs in the current energy transition arena and to implement an efficient renewable energy society. However, literature shows that are still open gaps concerning improvement of their energy density at high power, conversion efficiency, cost and cycle life. Electrodes based on active transition metal compounds, and in particular metal sulphides, evidence high potential to meet these objectives. This work discusses the dependence on the synthesis route of the charge storage mechanism of manganese sulphide-based materials and relates the pseudocapacitive response of these electrodes with their polycrystalline nature. Results reveal that a manganese oxy-sulphide mixture can achieve a high specific capacitance of 231 F.g−1 at 0.5 A/g in a 0.65 V active window. These values represent a 31.5 % increase compared to pure rambergite, γ-MnS, and 436 % compared to pure hausmannite Mn3O4 prepared under the same conditions. Moreover, the results show that manganese oxy-sulphide electrodes are characterized by good charge retention (73%), and superior long term capacity retention (above 86%) after 5000 cycles, evidencing potential for high power energy storage applications.

2021-09-01Journal article

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Influence of corrosion on the electrical and mechanical performance of hybrid busbars

Publication . Sampaio, Rui F. V.; Bragança, Ivo; Pragana, J. P. M; Silva, C. M. A.; Fernandes, João C. S.; Martins, Paulo A. F.

This paper is focused on the electrical and mechanical performance of aluminum-copper hybrid busbars subjected to corrosion over time. Two different types of hybrid busbars with joints produced by conventional fastening with M8 hexagonal socket head bolt-nut pairs made from medium carbon steel and by a new injection lap riveting process with semi-tubular rivets made from the material of the softer conductor are used and subjected to salt spray and electrochemical tests. Electrical resistance measurements performed on hybrid busbars taken from the corrosion testing cabinet at the end of each exposure period allow concluding that the new injection lap riveted hybrid busbars have a better electrical performance over time due to the elimination of fasteners with a higher electrical resistivity than aluminum and copper and to the elimination of the aluminum-steel and copper-steel galvanic pairs. The capability of the injection lap riveted hybrid busbars to withstand shear forces after corrosion testing also revealed to be adequate and like those of the original (uncorroded) hybrid busbars.

2022-06Journal article

Open access

Vanadium(V) complexes supported on porous MIL-100(Fe) as catalysts for the selective oxidation of toluene

Publication . Sutradhar, Manas; Marques, Guilherme; Soliman, Mohamed M. A.; Guedes Da Silva, M. Fátima C.; Flores, Daniela S. S.; Granadeiro, Carlos; Balula, Salete; Pombeiro, Armando; Alegria, Elisabete

The vanadium(V) complexes bearing the aroylhydrazone Schiff base 2-hydroxy-N'-((2-hydroxynaphthalen-1-yl) methylene)benzohydrazide ligand [VO(OMe)L] (1) and [Et3NH][VO2L] (2) were synthesized, characterized and supported on porous MIL-100(Fe) forming the 1@MIL-100(Fe) and 2@MIL-100(Fe) composites. The outcome of such immobilizations was assessed by several characterization techniques, namely powder X-ray diffraction, UV/ Vis, FTIR, SEM-EDS, ICP and BET surface area analysis, confirming the successful heterogenization of both va-nadium complexes. They were screened as catalysts towards the oxidation of toluene, under homogenous (1 and 2) and heterogeneous (1@MIL-100 and 2@MIL-100) conditions. The influence of several parameters, namely the type and amount of catalyst or oxidant, reaction time, temperature, and radical trapping, was studied. The main products obtained were benzaldehyde, benzyl alcohol and benzoic acid. Under the optimized conditions, using 1 and 2 as homogeneous catalysts, total yields of 19 and 23%, respectively, were achieved at 80 degrees C after 6 h. Using 1@MIL100(Fe) and 2@MIL100(Fe) composites under heterogeneous conditions, total yields up to 11% after 24 h, were achieved.

2022-08Journal article

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