One-pot synthesis, characterization and ammonia-selective catalytic reduction performance of MnSAPO-18 molecular sieves

Abstract

A one-pot synthetic method was used to prepare novel MnSAPO-18 catalysts with high crystallinity that were employed to efficiently scrub NOx in the flue-gas denitration reaction. In the controllable synthesis of MnSAPO-18, the effect of Mn content, organic amine templates, Mn precursors as well as hydrothermal crystallization time on the SCR performance of the resulting MnSAPO-18 catalysts and the structure-activity relationship of these samples was also investigated. The optimum combination of these variables in the hydrothermal synthesis process appeared to be using N,N-Diisopropylethylamine as the organic templates, manganese acetate as the Mn precursor, a crystallization time of 24 h and Mn content of n(MnO)/n(Al2O3) = 0.2 in the synthesis gel. The optimum Mn0.2SAPO-18-2 catalyst exhibited nearly 95% NOx conversion and 90% N2 selectivity in temperature range of 275–375 °C with a space velocity of 37,500 h−1. In the low-cost seed-assisted, one-pot synthesis of Mn0.2SAPO-18-1.0DIPEA-Seed, it was found that this sample had almost comparable activity as the Mn0.2SAPO-18-2 in the traditional one-pot method. These novel catalysts were characterized using the H2-TPR, NH3-TPD, XRD, FESEM, DR UV–Vis and ESR analysis. The results of these characterizations showed that the optimum SCR performance of Mn0.2SAPO-18-2 was closely related to its abundant high valence framework manganese, suitable surface acidity and high redox capability. Thus, Mn0.2SAPO-18-2 was shown to be a promising catalyst for NH3-SCR removal of NOx and this fabrication technique appeared to be potentially valuable for application in industry.