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 UO_x. As demonstrated by H₂-TPR, the uranium in the generated UO_x 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.