Perovskitas à base de La e Cu como catalisadores para a reação de redução do NO pelo CO

Abstract

The aim of this thesis was to synthesize and evaluate the performance of perovskite-like mixed oxides La2-xBaxCu1-yPdyO4-x/2, where x = 0 or 0.4 and y = 0 or 0.05, in the reduction reaction of NO by CO, focusing on their activity, selectivity and thermal stability. The catalysts were prepared by the coprecipitation method. The influence of the partial substitutions by Ba and/or Pd on the physical properties and the catalytic performance of the catalysts was evaluated. In addition, the impact on catalytic performance of the catalyst after thermal aging at 900 °C for 4 h was studied. Characterization tests such as ATG-ADT, N2 fisisorption, ICP-OES, XRD, TPD-O2, TPR-H2 and XANES were performed. For the catalytic evaluation, a mixture of 1% NO and 1% CO in He was used over a temperature ramp from room temperature to 500 °C. The characterization results indicated that the partial substitutions by Ba and/or Pd caused structural and physico-chemical changes in the catalysts, where the addition of Ba led to the formation of superficial oxygen vacancies and the addition of Pd promoted a greater reductibility of the catalysts. All the catalysts were active for the NO + CO reaction, but when subjected to thermal aging, the partial substitution of La by Ba increased the thermal stability of the perovskites. These results can be associated to the Cu+ species observed by XANES in the thermally aged catalyst containing Ba. The catalysts were even more active in their reduced form, where the previously reduced LaBaCuPd catalyst obtained the best performance among all the catalysts, reaching 100% of NO conversion at 310 °C. All catalysts had low N2O yield over the evaluated temperature range when compared to traditional supported catalysts