Hydrothermally modified nanosheet ZSM-5 with MnOx nanoparticles and its high MTP performance

Abstract Hydrothermally modified nanosheet ZSM-5 zeolite by directly using MnOx nanoparticles was carried out and this substantially offered a high performance catalyst for methanol to propylene (MTP) reaction. The properties of as synthesized ZSM-5 nanosheets with different MnOx amounts (NS-x) were compared with ZSM-5 nanosheets modified by impregnation method (IM-0.5) and physically mixed method (PM-0.5), respectively. The initial state of MnOx nanoparticles was close to Mn2O3 with 20 nm in size. XRD, H2-TPR and XAFS results confirmed under high temperature hydrothermal condition, the Mn2O3 nanoparticles disaggregated into Mn2O3 clusters and entered the framework defects of nanosheet zeolite with high dispersion. Infrared spectra of hydroxyl groups (OH-IR) showed that the Mn2O3 clusters were bonded with silanol defects both on the surface and inside zeolite, which substantially increased the stability of Mn2O3 clusters and healed the framework defects. In contrast, the Mn species in the impregnated sample was close to the co-existence of Mn2+ ions and MnO2 nanoparticles with 2–3 nm, no interaction between Mn species and Si–OH group was determined. Notably, the typical sample (NS-0.5) with MnOx cluster modification performed much higher propylene selectivity and catalytic stability (~52%, 240 h, WHSV = 3 h−1), while the conventional IM-0.5 and PM-0.5 showed poor propylene selectivity (48%, 46%) and catalytic stability (166 h, 133 h) in MTP reaction. The excellent result should be attributed to the subtle control of external strong acid and the less structural defects, due to specific existence of bonded Mn2O3 clusters.