CuO/cryptomelane catalyst for preferential oxidation of CO in the presence of H2: deactivation and regeneration

Abstract

Cryptomelane and CuO/cryptomelane catalysts have been tested in the preferential oxidation of CO in the presence of H₂ (CO-PROX reaction), paying special attention to deactivation and regeneration issues. Cryptomelane was stable during the CO-PROX reactions in ramp experiments until 200 °C and in a long-term isothermal experiment (10 h). Changes neither in the H₂ reducibility and porosity nor in the crystalline phases detected by XRD were observed. On the contrary, CuO/cryptomelane was partially deactivated during the consecutive CO-PROX reaction cycles performed until 200 °C, and the catalytic activity was partially restored by reoxidising the catalyst at 200 °C or 400 °C, the latter temperature being more effective. In spite of the CuO/cryptomelane partial deactivation, the CO-PROX activity of this catalyst was higher than that of cryptomelane once a stable behaviour was achieved. The partial deactivation of CuO/cryptomelane was attributed to the segregation of crystalline phases (hausmannite (Mn₃O₄) and/or hopcalite (CuMn₂O₄)), with the segregation of potassium to the surface and decrease in the copper cations' reducibility. The potential contribution to deactivation of the changes in the porous texture of CuO/cryptomelane was ruled out.