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.