Effect of composition and thermal treatment in catalysts derived from Cu-Al hydrotalcites-like compounds in the NO reduction by CO

Abstract In order to minimize the emission of pollutants in the atmosphere copper-based catalysts were studied. This is a cheaper alternative to traditional catalysts, which use noble metals. Catalysts for the NO by CO reduction reaction have been synthesized from Cu-Al type hydrotalcite with different compositions. The influence of thermal treatment at high temperatures, and the atmosphere of the pretreatment before catalytic tests, were also investigated. The characterization by chemical analysis, X-ray diffraction and thermal analysis indicated that pure hydrotalcite was obtained in the precursor with low Al/(Al + Cu) ratio, and that the catalysts were composed of mainly crystalline CuO and amorphous aluminum compounds. Temperature programmed reduction and in-situ XANES showed that some species of Cu + are present in the catalyst with 50:50 Cu:Al. After thermal treatments, CuO and copper aluminate were formed. All catalysts showed a very good performance, with conversion of 100% in most of them. The catalyst with the least N 2 O yield was the 50:50 Cu:Al. The corresponding precursor (50:50 Cu:Al) treated at 900 °C for 12 h improved clearly the activity, and when it was in-situ reduced (before catalytic test) it was most active in comparison to the other catalysts that were evaluated.