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  • Polyoxometalate@Periodic mesoporous organosilicas as active materials for oxidative desulfurization of diesels
    Publication . Ribeiro, Susana; Almeida, Pedro L.; Pires, João; De Castro, Baltazar; Balula, Salete
    Novel 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.
    2020-08-01Journal article Restricted access Show more
  • Design optimization of functionally graded plates under thermo-mechanical loadings to minimize stress, deformation and mass
    Publication . Moleiro, Filipa; Madeira, Jose Firmino Aguilar; Carrera, Erasmo; Reddy, J. N.
    This work addresses the multiobjective design optimization of metal-ceramic functionally graded (FG) plates, which are composed of a main functionally graded material (FGM) layer and may include metal and/or ceramic faces, under thermo-mechanical loadings. The design variables are the thickness of the FGM layer, the index of its power-law distribution of metal-ceramic volume fractions, and if included, the thickness of the metal and/or ceramic faces. The three objectives focus on mass, maximum transverse displacement and maximum value of the Tsai-Hill failure criteria to measure the stress field, aiming to minimize all together. Both thermal and mechanical problems are solved simultaneously using a layerwise mixed model based on least-squares formulation with multi-field independent variables, namely, displacements, temperature, transverse stresses, transverse heat flux, in-plane strains and in-plane components of the thermal gradient. The FGM layer z-continuous effective properties are fully described via high-order z-expansions, similarly to finite element approximations. The multiobjective optimization problem is solved by Direct MultiSearch (DMS) derivative-free method, which uses the notion of Pareto dominance to retain a list of feasible non-dominated solutions. Numerical results provide optimal designs of FG plates under thermo-mechanical loadings, exploring distinct metal-ceramic constituent materials and different side-to-thickness ratios, including three-dimensional approximate solutions for validation.
    2020-08-01Journal article Restricted access Show more