Depleted uranium catalysts for chlorine production

Abstract

This study demonstrates depleted uranium as a remarkable heterogeneous catalyst for the oxidation of HCl to Cl2. This reaction comprises a sustainable approach to valorise byproduct HCl streams in the chemical industry. Bulk α-U3O8 showed an outstanding stability against chlorination, which is crucial for its durability in catalytic tests. UO2 and γ-UO3 transformed into α-U3O8 under reaction conditions. Uranium deposition on different carriers by dry impregnation concluded the superiority of zirconia as support. HAADF-STEM investigations revealed that the uranium oxide on the surface of this carrier is present in the form of a film-like nanostructure with a thickness ranging from a monolayer to 1 nm as well as atomic dispersion. The effect of variables (temperature, feed O2/HCl ratio, metal loading, and Cl2 co-feeding) on the performance of U3O8/ZrO2 has been studied. The HCl conversion over this catalyst increased with reaction time as a likely consequence of in situ re-dispersion of the original uranium phase into atomically dispersed UOx. As demonstrated by H2-TPR, the uranium in the generated UOx phase is more oxidised than in the original U3O8. Such a highly dispersed active phase is produced faster in the uncalcined sample. The extraordinary stable Cl2 production over U3O8/ZrO2 at 773 K for 100 h on stream indicates its potential for application in high-temperature HCl oxidation. Under these conditions, other known catalytic materials suffer from significant deactivation. © 2013 Royal Society of Chemistry.