[en] Results of a study on the purifier system used at the Closed Loop recirculation gas plant of the CMS experiment at the CERN LHC are reported. Previous studies have focused the attention on pollutant and gas analyses. This study mainly deal with characterization of new, used and regenerated metallic purifiers by XRD analyses and thermodynamic simulations. The study is focused on the regeneration processes of the metals, including the reaction mechanisms of copper, zinc and nickel reduction/oxidation and confirms the purifying system efficiency towards the O₂. Partial reduction of CuO to Cu₂O and a not complete reduction to Cu is evident from data reported for copper based purifier. Results discussed provide a complete understanding of both filtration process and reactions implied in the system, thus preluding to optimization of regeneration procedures