Conversion of NH3-NOx in gasified biomass over LaMnAl11O19 catalyst

LaMnAl11O19 catalysts were prepared by co-precipitation method and characterized by XRD, BET, and XPS. The conversion of NH3 under the conditions of catalytic and homogeneous combustion was studied by the combustion of simulated biomass gasification gas and NH3 oxidation, respectively. Moreover, the NH3 adsorption and oxidation on the surfaces of the catalyst samples were examined by in-situ DRIFT experiments. It was found that calcination of the precursors at 1200°C led to the formation of a final monophasic material with an MP structure and a high surface area, whereas the Mn ions were either divalent or trivalent. Under homogeneous combustion condition, NH3 in a simulated biomass gasification gas started reacting at 500°C; then, NO was formed. Under catalytic combustion condition, the curves of NH3 oxidation both with and without addition of simulated gasification gas showed no obvious differences. NH3 started reacting at 310°C, and NO exhibited a higher concentration in the temperature range of approximately 350–800°C. However, NO2 was generated at a higher temperature within a narrow temperature range. The concentration of N2O during the reaction was less than 10 × 10−6. More than 40% of the NH3 was converted to NO during the experiment. The results of in-situ DRIFT indicated that the reaction of ammonia conversion followed the imide (-NH) mechanism, that is, the ammonia adsorbed on the catalyst surface was first decomposed to -NH, then the -NH reacted with atomic oxygen (O) to further form nitroxyl (HNO) and N2 or nitrous oxide (N2O), or −NH reacted with molecular O2 to produce nitric oxide (NO) directly.