Selective catalytic oxidation of ammonia over LaMAl11O19−δ (M = Fe, Cu, Co, and Mn) hexaaluminates catalysts at high temperatures in the Claus process

Abstract

A method for the selective catalytic oxidation of ammonia at high temperature was innovatively proposed to substitute the traditional combustion method to remove the ammonia impurity in the Claus process. In the present work, transition metal (Fe, Cu Co, and Mn)-substituted La-hexaaluminate catalysts were synthesized and investigated for the selective catalytic oxidation of ammonia (NH₃-SCO) at high temperature. It was observed that Cu-substituted catalysts could achieve the highest N₂ yield at around 520 °C. It was confirmed that the conversion of NH₃ was closely related to the reducibility of the prepared catalyst. In particular, it was observed that the molecular O₂ could not be dissociatively adsorbed on the prepared catalyst surface. However, both lattice oxygen and gas-phase O₂ could participate in NH₃-SCO, with gas-phase O₂ being the most favorable under the experimental conditions. It was evidenced that the NH₃-SCO reaction over the prepared catalysts followed the i-SCR mechanism. Moreover, monodentate nitrates were the main reactive intermediates toward forming N₂. Therefore, the development of high-temperature SCO technology and an efficient catalyst are beneficial for the sustainable development of the chemical industry.