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- Polyoxometalate@Periodic mesoporous organosilicas as active materials for oxidative desulfurization of dieselsPublication . Ribeiro, Susana; Almeida, Pedro L.; Pires, João; De Castro, Baltazar; Balula, SaleteNovel material catalysts based in the active zinc-substituted polyoxotungstate ([PW11Zn(H2O)(39)](5-), abbreviated as PW11Zn) were efficiently used in the oxidative desulfurization of real and model diesels. These active catalytic center was strategically immobilized in a less hydrophilic periodic mesoporous organosilicas (PMOs), containing ethane-bridge (PMOE) and benzene-bridge (PMOB) walls, functionalized with (3-aminopropyl)triethoxysilane (aptes). The efficiency of the novel catalytic composites (PW11Zn@aptesPMOE and PM11Zn@aptesPMOB) was studied under oxidative desulfurization system (CODS) without the presence of an extraction solvent and also using a biphasic (diesel/extraction solvent) oxidative desulfurization system (ECODS). Both composites presented higher desulfurization efficiency under the solvent-free system, reaching ultra-low levels of sulfur compounds after only 1 h and using low ratio of H2O2/S = 4. The catalysts could be recycled without loss of activity for ten consecutive cycles. However, after the first desulfurization cycle complete desulfurization was achieved within only 30 min using PW11Zn@aptesPMOE composite. Also, the structure of PW it Zn@aptesPMOE demonstrated to be more stable than PW11Zn@aptesPMOB, probably due to the occurrence of some PW11Zn leaching from the PMOB surface, probably caused by the lower interaction of PW11Zn with the benzene-bridge PMOB wall. The most robust catalyst PW11Zn@aptesPMOE was used to desulfurize a real diesel achieving 75.9% of desulfurization after 2 h. The catalyst was further recycled with success to treat real diesel.
- Effective zinc-substituted keggin composite to catalyze the removal of sulfur from real diesels under a solvent-free systemPublication . Ribeiro, Susana; Granadeiro, Carlos; Almeida, Pedro L.; Pires, João; Valença, Rita; Campos-Martin, J. M.; Ribeiro, Jorge C.; De Castro, Baltazar; Balula, SaleteThe 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.
- Oxidative desulfurization strategies using Keggin-type polyoxometalate catalysts: Biphasic versus solvent-free systemsPublication . Ribeiro, Susana; Granadeiro, Carlos; Almeida, Pedro L.; Pires, João; Capel-Sanchez, Maria C.; Campos-Martin, J. M.; Gago, S.; De Castro, Baltazar; Balula, SaleteStrategic 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.
- Efficient heterogeneous polyoxometalate-hybrid catalysts for the oxidative desulfurization of fuelsPublication . Mirante, Fátima; Dias, Luís; Silva, Mariana; Ribeiro, Susana; Corvo, Marta C.; De Castro, Baltazar; Granadeiro, Carlos; Balula, SaleteThe heterogenization of the highly active monovacant polyoxotungstate ([PW11O39](7-), abbreviated as PW11) was achieved by preparing the corresponding long chain quaternary ammonium salt (ODA(7)PW(11), ODA = CH3(CH2)(17)(CH3)(3)N). The complete cation exchange confers total heterogeneity to the monovacant catalyst while keeping its oxidative catalytic activity. In fact, the heterogeneous catalyst allowed for the complete desulfurization of a multicomponent model diesel (2000 ppm S) after 40 min of reaction, conciliating extraction (using BMIMPF6 solvent) and oxidation (ECODS process using H2O2 oxidant). The heterogeneous catalyst has shown a superior desulfurization performance when compared with the homogeneous quaternary ammonium TBAPW(11) catalyst (TBA = (C4H9)(4) N). Both hybrid catalysts have been successfully reused in consecutive ECODS cycles. Additionally, the long carbon chain cations provide a protective environment around the polyoxometalate allowing for ODA(7)PW(11) to retain its heterogeneity and structure after the ECODS process.
- A novel red emitting material based on polyoxometalate@periodic mesoporous organosilicaPublication . Granadeiro, Carlos; Ribeiro, Susana; Kaczmarek, Anna M.; Cunha-Silva, Luis; Almeida, Pedro L.; Gago, Sandra; Van Deun, Rik; De Castro, Baltazar; Balula, SaleteThe first lanthanopolyoxometalate-supported bifunctional periodic mesoporous organosilica (BPMO) composite is here reported. The incorporation of decatunsgstoeuropate anions ([Eu(W5O18)(2)](9-)) within the porous channels of an ethylene-bridged TIVIAPS-functionalized BPMO produced a luminescent material exhibiting a strong red emission under UV irradiation. Photoluminescence studies showed an efficient energy transfer process to the lanthanide emitting center in the material (antenna effect). A significant change in the coordination environment of Eu3+ ions was observed after its incorporation into the TMAPS-functionalized material. The possible reason for this is discussed within the paper.