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Cyclic carbonate synthesis from CO2 and epoxides using zinc(II) complexes of arylhydrazones of beta-diketones

Publication . Moreno Montoya, Carmen Alicia; Gomez, Clara F.; Paninho, Ana B.; Nunes, Ana V. M.; Mahmudov, Kamran; Najdanovic-Visak, Vesna; Martins, Luisa; Guedes Da Silva, M. Fátima C.; Pombeiro, Armando; Nunes Da Ponte, Manuel

Zinc(II) complexes of arylhydrazones of beta-diketones (AHBD) were used for the first time as catalysts combined with tetrabutylammonium bromide (TBABr), in the coupling reaction between CO2 and epoxides. The influence of pressure and temperature on cyclic carbonate formation was investigated, as well as the catalytic activity toward different substrates (e.g. styrene oxide, propylene oxide and cyclohexene oxide). The molar ratio between metal complex and TBABr was determined for maximum catalytic activity.

2016-03Journal article

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Oxidative desulfurization strategies using Keggin-type polyoxometalate catalysts: Biphasic versus solvent-free systems

Publication . Ribeiro, Susana; Granadeiro, Carlos; Almeida, Pedro L.; Pires, João; Capel-Sanchez, Maria C.; Campos-Martin, J. M.; Gago, S.; De Castro, Baltazar; Balula, Salete

Strategic polyoxometalate Keggin-type structural modification was performed to increase the oxidative catalytic performance to desulfurize model and real diesels. The most active lacunar structure [PW11O39](7-) (PW11) showed to complete desulfurize a simulated diesel after 60 min at 70 degrees C. Its application as homogeneous catalyst using a biphasic system 1: 1 diesel/acetonitrile needed to use an excess of oxidant (ratio H2O2/S = 8). The immobilization of the PW11 on amine-functionalized SBA-15 supports originated two heterogeneous catalysts PW11@aptesSBA-15 and PW11@tbaSBA-15. The best results were attained with the PW11@aptesSBA-15 catalyst showing identical oxidative desulfurization performance as the homogeneous analogue. As advantage, this heterogeneous catalyst promotes the complete desulfurization of simulated diesel using a solvent-free system, i.e. without the need of acetonitrile use. On the other hand, the same desulfurization efficiency could be achieved using half the amount of oxidant (H2O2/S = 4). The oxidative desulfurization of the real diesel achieved a remarkable 83.4% of efficiency after just 2 h. The recycling capacity of PW11@aptesSBA-15 catalyst was confirmed for eight consecutive cycles using the biphasic and the solvent-free systems. Its stability investigation demonstrates to be higher under the solvent-free system than the biphasic system, without practically any occurrence of PW11 leaching in the first case. On the other hand, the Venturello peroxocomplex [PO4{W(O-2)(2)}(4)](3-), recognized as active intermediate in the homogeneous biphasic system, was not identified in the heterogeneous catalytic systems.

2019-08-01Journal article

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Effective zinc-substituted keggin composite to catalyze the removal of sulfur from real diesels under a solvent-free system

Publication . Ribeiro, Susana; Granadeiro, Carlos; Almeida, Pedro L.; Pires, João; Valença, Rita; Campos-Martin, J. M.; Ribeiro, Jorge C.; De Castro, Baltazar; Balula, Salete

The Keggin phosphotungstate (PW12) and its zinc derivative (PW11Zn) were tested as oxidative catalysts for desulfurization processes using simulated and real diesels. These compounds were used as homogeneous catalysts, while the corresponding SBA-15 composites were used as heterogeneous catalysts. The comparison of their catalytic performance demonstrated that the zinc-substituted polyoxometalate is more eﬃcient than the plenary PW12 structure. Additionally, using the heterogeneous PW11Zn@aptesSBA-15, the sustainability and catalytic eﬃciency was largely improved, allowing the total sulfur removal from model diesel after 1 h using a small amount of oxidant (H2O2/S = 4) under an oxidative solvent-free system. The desulfurization of real diesels was performed under similar conditions, achieving 87.8% of eﬃciency using the PW11Zn@aptesSBA-15 catalyst. Furthermore, the catalyst maintained its activity over consecutive desulfurization cycles. The cost-eﬀective operational conditions achieved with PW11Zn@aptesSBA-15 turn this into a promising material to be used in an industrial scale to treat diesel.

2019-10-09Journal article

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Biomass-derived nanoporous carbons as electrocatalysts for oxygen reduction reaction

Publication . Fernandes, Diana M; Mestre, Ana S.; Martins, Angela; Nunes, Nelson; Carvalho, A. P.; Freire, Cristina

Electrocatalysts (ECs) for the oxygen reduction reaction (ORR) are crucial in fuel cells and for this reason developing cost-effective metal-free ECs with high electrocatalytic activity and high-volume production remains a huge challenge. Herein, we report the application as ORR electrocatalysts of a series of high grade nanoporous carbons, prepared by chemical activation of acid-chars obtained from the H2SO4 digestion and polycondensation (acid-mediated carbonization) of a biomass residue (Agave sisalana). All the nanoporous carbons presented good ORR electrocatalytic activities in alkaline medium. The AC(1) carbon exhibited the most promising ORR performance with E-onset = 0.84 vs. RHE, j(L, 0.26 V, 1600 rpm) = -3.12 mA cm(-2) and n(O2) = 3.6 electrons. The Tafel slopes of all carbons varied between 47 mV dec(-1) (AC(3)) and 250 mV dec(-1) (AC(1)). Furthermore, the carbons revealed superior tolerance to methanol when compared with commercial Pt/C and a competitive long-term electrochemical stability, with current retentions of 75-85 % after 20,000 s. The results obtained in this work suggest a promising method based on sustainable and economical biomass residues towards the development and engineering of novel value-added biomass-derived carbons as effective metal-free electrocatalysts for alkaline fuel cells.

2020-11-01Journal article

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Vanadium C-scorpionate supported on mesoporous aptes-functionalized SBA-15 as catalyst for the peroxidative oxidation of benzyl alcohol

Publication . Correia, Luís M. M.; Soliman, Mohamed Mostafa Aboelhassan; Granadeiro, Carlos; Balula, Salete; Martins, Luisa; Pombeiro, Armando; Alegria, Elisabete

The neutral trichloro[hydrotris(1-pyrazolyl)methane]vanadium(III) [VCl3(Tpm)] (Tpm = HC(pz)(3); pz = pyrazolyl) C-scorpionate complex was immobilized on amine-functionalized mesoporous silica (aptesSBA-15) via an impregnation method forming the [VCl3(Tpm)]@aptesSBA-15 composite. The immobilization of the vanadium compound was confirmed by several characterization techniques, namely SEM/EDS, powder XRD, FT-IR/ATR, ICP and BET surface area analysis, revealing the successful incorporation of the complex, and confirming the structural and morphological preservation of the porous support and the vanadium complex. The vanadium composite was tested as heterogeneous catalyst for the peroxidative oxidation of benzyl alcohol under mild conditions and its catalytic performance was compared to that of the analogous homogeneous [VCl3(Tpm)] complex. The catalytic studies were extended to other substrates. The effect of various parameters, such as amount and type of oxidant, catalyst and additives, temperature and reaction time were investigated allowing to reach overall yields of ca. 60% and turnover numbers (TONs) up to ca. 7.6 x 10(3). The results obtained demonstrated the higher performance of the heterogeneous catalyst using much less [VCl3(Tpm)] complex under a solvent-free system. Furthermore, consecutive reaction cycles could be performed, showing its recycling capacity. Structural stability was also investigated, indicating the viability of the vanadium C-scorpionate composite as catalyst for other oxidative reactions with high industrial interest.

2021-06Journal article

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