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Osegueda O.,Rovira i Virgili University | Osegueda O.,as Research Center on Engineering of Materials and Micro nanoSystems | Osegueda O.,Jose Simeon Canas Central American University | Dafinov A.,Rovira i Virgili University | And 6 more authors.
Catalysis Today | Year: 2012

Commercial ceramic hollow fibres have been used as a starting material for the preparation of catalytic membrane reactors (CMRs). The original nominal pore sizes of the membranes were 4, 20, 100, 500 and 1400 nm. The CMRs have been produced by palladium precursor impregnation followed by calcinations and reduction in hydrogen flow at 350 °C. The direct generation of hydrogen peroxide from hydrogen and oxygen has been studied at ambient conditions. The efficiency of hydrogen peroxide generation, with respect to hydrogen supply, as well as the rate of H 2O 2 production and the maximum H 2O 2 concentration as a function of the original membrane pore size have been determined. The μ-XRD and SEM analyses have revealed that the Pd is uniformly distributed throughout the entire membranes. The rate of hydrogen peroxide generation has been shown to depend inversely on the membrane pore size. It has been demonstrated that the upper hydrogen peroxide concentration level is set by the catalyst deactivation and therefore not caused by reverse reactions or hydrogen peroxide reduction by the activated hydrogen. This finding has been confirmed by the XPS analysis. The in situ oxidation of phenol by a subsequent heterogeneous Fenton process in phenol-containing water has been assessed using the CMRs prepared. In these cases no significant activity has been detected. Addition of Fe(II) to the reaction solution has resulted in CMRs with considerable activity for phenol oxidation. In another series of ceramic hollow fibre membranes, the Pd impregnation was preceded by the incorporation of a second active phase (Fe 2O 3, CuAl 2O 4, TiO 2 or CeO 2). The rates of hydrogen peroxide generation as well as the maximum H 2O 2 concentration for these bi-functional CMRs have been determined following the same procedure developed for the first series of CMRs. All of them have shown activity in producing H 2O 2. The initial tests for phenol oxidation by the in situ generated H 2O 2 have demonstrated the viability of the proposed reaction system for waste water treatment. © 2012 Elsevier B.V. Source


Osegueda O.,Rovira i Virgili University | Osegueda O.,as Research Center on Engineering of Materials and Micro nanoSystems | Osegueda O.,Jose Simeon Canas Central American University | Dafinov A.,Rovira i Virgili University | And 6 more authors.
Chemical Engineering Journal | Year: 2015

This work presents a novel method for oxidation of organic matter in water solutions based on catalytic membrane reactors. The oxidant, hydrogen peroxide, is generated directly in the bulk of the liquid investigated. Commercial symmetric alumina hollow fibers have been used as a starting material thereafter introducing the active phases. It has been proven that two different catalysts are necessary in order to complete the overall reaction, as well as to generate hydrogen peroxide and a heterogeneous Fenton process. Palladium has been used for the hydrogen peroxide generation and a second active phase, transitional metal oxides or homogeneous Fe2+, has been used for the hydroxyl radical generation. An additional method for specific Pd loading to the reaction zone based on sputtering technique has been developed. All prepared catalytic membrane reactors (CMRs) are capable of generating hydrogen peroxide in amounts comparable to CMRs reported in the literature. The catalytic membrane reactors prepared by Pd impregnation show very high activity and stability in phenol oxidation reaching 40% of the generated H2O2 usage in the oxidation reaction. Despite the very high activity of the catalytic membrane reactors obtained by Pd sputtering in H2O2 production they suffer very fast deactivation. Specific reactivation including a calcination step has been found to be appropriate for the recovery of their activity. Additional experiments give new insights for better understanding of Pd deactivation especially when the metal particles are of nanometer sizes. © 2014 Elsevier B.V. Source

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