SYNTHESIS AND CHARACTERIZATION OF EUROPIUM-DOPED CRYPTOMELANE FOR THE CATALYTIC OXIDATION OF ETHANOL

The mineral cryptomelane (KMn⁴⁺, Mn²⁺)₈O₁₆) is an attractive catalyst owing to its high surface area, mesoporosity, hydrophobicity, and high oxygen mobility but more importantly its low-cost, ease of synthesis, and ability to be enhanced with promoters. In this investigation, cryptomelane was synthesized and promoted with europium (Eu) to explore the resulting effects on its physical, chemical, and catalytic properties. Synthesis of a Eu-doped cryptomelane has not yet been done and is being pursued because of significant catalytic activity improvement reported from cerium-doping - Ce being a chemically similar element to Eu.

Syntheses were carried out by solid-state and reflux methods and Eu was incorporated by co-precipitation and by ion-exchange; along with undoped controls this yielded six unique sample types. An extensive suit of analyses were used to determine the (1) nature of the crystal structure and morphology, (2) surface and pore geometry, (3) thermal properties, (4) bulk chemistry and Mn oxidation state, and (5) catalytic activity. The cryptomelane samples were evaluated in the catalytic oxidation of ethanol, a 1^st order reaction that cryptomelane has previously been demonstrated to be active for.

Overall, Eu introduced properties into cryptomelane that are considered catalytically favorable: structural defects, smaller crystal size, higher surface area, greater mesoporosity, improved thermal stability, and increased valence oxygen. Each synthesis method yielded different results with respect to reaction rate and activation energy that were consistent with these measured changes in properties, with the solid-state cryptomelane Eu-doped via co-precipitation showing the most improvement relative to its undoped equivalent in terms of activation energy (E_a = 29.2 kJ/mole vs. 62.9 kJ/mole).