Chapter 5.5 - Inorganic materials (metals, ceramics, glasses) under the influence of reactants in supercritical aqueous solutions as well as Chemical reactions (partial oxidations, hydrolysis, dehydrations) under the influence of inorganic materials in supercritical aqueous solutions

Abstract

This chapter discusses about the inorganic materials under the influence of reactants in supercritical aqueous solutions, as well as chemical reactions under the influence of inorganic materials in supercritical aqueous solutions. Supercritical water (SCW) has been growing in importance as a medium for chemical reactions. Corrosion studies of metals showed that most investigated metals were stable in pure SCW. For reactions in oxygen containing SCW palladium and copper appear to be suitable as catalysts. In corrosion tests of ceramic materials in SCW aluminium titanate, A12O3- and TiO2-ceramics proved to be stable. TiO2-ceramic was used as a platinum supported carrier in the partial oxidation of m-xylene and the hydrogenation of cyclohexene. Chemical syntheses such as partial oxidation, hydrolysis, dehydration, and hydrogenation can be carried out in SCW. Partial oxidations are possible in SCW, but show several problems. The hydrogenation of cyclo­hexene to cyclohexane by addition of formic acid, which decomposed to hy­drogen and carbon dioxide, was successful. The cyclohexene was formed in situ by the dehydration of cyclohexanol. In several reactions, especially in partial oxida­tions, catalysts were examined, but they either promote above all the forma­tion of the total oxidation products or have no influence on the reaction at all.