In situ generation of hydrogen peroxide in catalytic membrane reactors

Abstract

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 1400nm. 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 H2O2 production and the maximum H2O2 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 (Fe2O3, CuAl2O4, TiO2 or CeO2). The rates of hydrogen peroxide generation as well as the maximum H2O2 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 H2O2. The initial tests for phenol oxidation by the in situ generated H2O2 have demonstrated the viability of the proposed reaction system for waste water treatment.