(374g) The Effect of Nanostructured Mnox Crystallographic Phase and Particle Size in the Catalytic Decomposition of Hydrogen Peroxide for Environmental Remediation of Effluents

Product solutions or effluents of peroxygen reactions may contain variable amounts of unreacted peroxide, usually in the form of hydrogen peroxide, percarboxylic acids, and/or organic peroxide. For reasons related to safety, waste treatment or product stability, it is usually necessary to destroy unreacted peroxide species in the product solution or effluent prior to discharge or workup, and certainly before any product concentration process. A possible treatment of such effluents contaminated with unreacted peroxides can be through catalytic decomposition. The most active catalysts for these reactions are Mn-based oxides. The use of nanostructured catalyst is expected to increase activity and reaction kinetics in such systems. Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen peroxide. The effect of type of precipitant (Na2CO3 y NH4OH) over the particle size, crystallographic phase and catalytic activity was established. Characterization of the obtained nanoparticles was performed through XRD analysis, BET surface area and TEM microscopy. Catalytic activity was followed through gasometry of the oxygen evolution [H2O2(l) = H2O(l) + O2 (g)] at 25°C. Results indicate that the catalyst synthesized using Na2CO3 (Mn-1) as precipitant produced 5-10 nm nanoparticles, while, catalyst from NH4OH (Mn-2) produced 20 nm nanoparticles. This result was attributed to greater pH stability (Na2CO3) during the precipitation process. XRD results revealed delta-MnO2 for Mn-1 and Mn5O8 for Mn-2 catalysts. Catalytic activity resulted in intrinsic rate constants (kint = min-1g-1) of 5.2 and 2.3 for Mn-1 and Mn-2, respectively. The greater catalytic activity was attributed to the presence of Mn5O8 phase.