Preparation of nanosized Mn3O4/SBA-15 catalyst for complete oxidation of low concentration EtOH in aqueous solution with H2O2

Abstract

A new heterogeneous Fenton-like system consisting of nano-composite Mn3O4/SBA-15 catalyst has been developed for the complete oxidation of low concentration ethanol (100ppm) by H2O2 in aqueous solution. A novel preparation method has been developed to synthesize nanoparticles of Mn3O4 by thermolysis of manganese (II) acetylacetonate on SBA-15. Mn3O4/SBA-15 was characterized by various techniques like TEM, XRD, Raman spectroscopy and N2 adsorption isotherms. TEM images demonstrate that Mn3O4 nanocrystals located mainly inside the SBA-15 pores. The reaction rate for ethanol oxidation can be strongly affected by several factors, including reaction temperature, pH value, catalyst/solution ratio and concentration of ethanol. A plausible reaction mechanism has been proposed in order to explain the kinetic data. The rate for the reaction is supposed to associate with the concentration of intermediates (radicals: OH, O2− and HO2) that are derived from the decomposition of H2O2 during reaction. The complete oxidation of ethanol can be remarkably improved only under the circumstances: (i) the intermediates are stabilized, such as stronger acidic conditions and high temperature or (ii) scavenging those radicals is reduced, such as less amount of catalyst and high concentration of reactant. Nevertheless, the reactivity of the presented catalytic system is still lower comparing to the conventional homogenous Fenton process, Fe2+/H2O2. A possible reason is that the concentration of intermediates in the latter is relatively high.