Catalisadores La-Cu-Al para a reação de redução do NO pelo CO

Abstract

In recent years, new types of catalysts are being studied to reduce NOx emissions into the atmosphere, due to the contaminating potential of nitrogen oxides, mainly N2O, which is a highly harmful greenhouse gas. Usually, catalysts composed of noble metals are used, which present several disadvantages, highlighting their high cost and the significant formation of N2O, mainly during cold emissions. In order to seek the development of low cost and high activity catalysts, the present dissertation sought to study the influence of lanthanum in copper and aluminum catalysts, in the reaction of reducing NO by CO, aiming at improving catalytic activity, in addition to evaluating the influence of different preparation methods and the thermal stability of the catalysts. This aspect is also relevant considering the high temperatures to which these catalysts are subjected. The precursor method by coprecipitation was used, in continuous mode (CuAlHT and LaCuAlHT) in order to obtain the hydrotalcite phase, the impregnation method (La/CuAlHT) and the solid state reaction method (CuAlRS and LaCuAlRS). From the XRD analysis, it was verified, for the precursors, the obtaining of the pure hydrotalcite phase. After calcination of the precursors at 600 °C, only the crystalline phase of CuO was observed; whereas those aged at 900 and 1000 °C showed the crystalline phases of CuO and CuAl2O4. The CuAlHT900 catalyst showed the highest reducibility among new and aged catalysts. The analysis of X-ray absorption spectroscopy indicated that initially, the CuAlHT600 and CuAlHT900 catalysts mainly have Cu2+ species, however, after reduction CuAlHT600 presented only the Cu0 species, and CuAlHT900 presented the Cu+ and Cu0 species, with Cu+ in greater quantity. The catalysts aged at 900 °C showed better catalytic activity when compared to the new ones, except for the La/CuAlHT900 catalyst. This improvement is probably due to the presence of copper aluminate species in aged catalysts. When aged at 1000 °C, only CuAlHT1000 showed better activity compared to the new catalyst, and the catalysts synthesized by reaction in solid state suffered deactivation, probably due to the effect of high temperatures of thermal aging. The catalysts synthesized by reaction in solid state based on La, LaCuAlRS600 and LaCuAlRS900, showed less formation of N2O because they are less active at low temperatures.