Influência do potássio em óxidos mistos à base de cobre na reação de redução do NO e N2O pelo CO

Abstract

Among nitrogen oxides, N2O is a greenhouse gas with a highly harmful effect, because of that, it is important to implement processes in order to reduce its emission, as well as other NOx. The most common catalysts used in NOx reduction are based on noble metals and have two important limitations: the high price and the formation of nitrous oxide at low temperatures. In this study, alternative copper-based catalysts with different structures like hydrotalcite, perovskite and spinel were impregnated with potassium and evaluated in the reduction reaction of NO by CO. This dissertation aims to evaluate the influence of potassium in the reducibility of the metal in reaction selectivity, as well as its role in NOx storage. The samples were impregnated in each support with 0.06, 0.6 and 10 K/Cu (mol / mol). The results of X-ray diffraction indicated the presence of the K2CO3 phase in hydrotalcite and spinel type catalysts with higher amounts of potassium. The perovskite type catalyst with a higher amount of potassium presented the K2O phase form at around 270 °C in reducing atmosphere.The reducing behavior of the catalysts and the positive influence of potassium were observed through H2-TPR. The best catalysts were those with 0.06 K/Cu (mol / mol) for hydrotalcite catalysts and 0.6 for spinel ones and these were monitored by XRD and XANES in situ. The results demonstrate a presence of Cu0 and Cu +1 as catalysts, proving a high efficiency of a reduced surface, which promotes the reduction of N2O reduction reactions by CO, as already reported in the literature. In the perovskite type catalysts, potassium did not improve the reducibility and, therefore, did not positively influence the activity, however there was no formation of N2O in the catalysts with potassium. The alkali metal, depending on the structure, worked to improve the reducibility or to store NOx, enhancing, in all cases, the selectivity to N2.