Estudo de catalisadores contendo cobre para a reação de redução de NO pelo CO

Abstract

This study focuses mainly on the investigation of the influence of the preparation methods on the redox behavior and the structural thermal stability of Cu and Al based catalysts in order to improve the catalytic activity for NO reduction by CO. The physical mixing of the oxides method (CuAl-o), the solid-state reaction method (CuAl-s) and the precursor method (CuAl-p, CuAl-HT-c and Cu-p) were used. For the CuAl-HT-c catalyst, the precursor method was used to obtain the hydrotalcite phase, obtaining a high purity precursor and a catalyst with advantages over other preparation methods, such as greater surface area and greater reducibility. In addition, it can be said that this catalyst proved to be structurally and texturally more stable (by XRD in situ), as it maintained its crystal size throughout the heat treatment up to 500 ° C. By analyzing the pre-treatment effect under inert atmosphere for all catalysts, the hydrotalcite-derived catalyst showed a significant reduction from 440 ° C, with the formation of Cu2O and Cu foil confirmed by XRD and XANES, both in situ. In a first cycle of NO reduction by CO, the catalyst CuAl-HT-c is not the most active, however, its activity improves after a second cycle of reaction, which was attributed to the diffusion of the active species to the surface. Furthermore, the impact of thermal treatment at 900 ° C for 12 h resulted in a catalyst (CuAl-HT-c_env) composed of a mixture of CuO and CuAl2O4, as well as a significant drop in the surface area. However, the results of the catalytic tests showed that no thermal deactivation occurred, improving the catalytic activity in relation to the calcined catalyst, which was related to Cu+ formation, oxygen vacancy and thermal stability. After pretreatment with H2, the CuAl-HT-c catalyst showed the best catalytic performance, reaching 100% conversion at 200 ° C, when the formation of the N2O pollutant is no longer present. All other catalysts demonstrated deactivation, possibly by the agglomeration of copper foil. Finally, this thesis shows that catalyst preparation methods lead to different formations of reduced copper species during pretreatment and NO reduction by CO reaction. The formation of N2O appears to be favored mainly by the presence of Cu+ and possibly by the low reactivity of the reaction of reduction of N2O by copper foil