Selective reduction of NO by CO using copper-aluminum oxides from hydrotalcite-type precursors: Study of chemical species and thermal stability

Abstract

The objective of this work was to analyze the influence of Al on copper catalysts, regarding thermal stability and performance during NO reduction by CO. Two copper-based catalysts were prepared by precipitation and subsequent calcination at 600 °C, with and without aluminum in their composition (CuAl-HT-c and Cu-p). The precursor CuAl-HT was synthesized to obtain a hydrotalcite structure. The catalysts obtained after calcination of the precursors were characterized by N2 physisorption, TPR, N2O titration, in situ XRD and in situ XANES. They showed good catalytic performance, however with Cu-p being the most active but with larger formation of N2O (important greenhouse gas). In this catalyst, the interaction between the adsorbed NO molecules is facilitated, probably due to the higher concentration of Cu+.Regarding the aged catalysts, Cu-p was deactivated due to sintering, which is attributed to the lack of aluminum. CuAl-HT-c-900 had its performance improved during aging, either because the reduction of NO by CO is a structure-sensitive reaction for this catalyst (and the increase in particle size after aging is related to larger activity), or because of the presence of copper aluminate, which can also improve activity and selectivity.