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- 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.