Organotemplate-free and seed-directed synthesis of ZSM-34 zeolite with good performance in methanol-to-olefins

Abstract

The methanol-to-olefins (MTO) reaction over zeolites is of great importance due to the shortage of crude oil, and we demonstrate here a fast, organotemplate-free, and seed-directed synthesis of ZSM-34 zeolite, designated as ZSM-34-S, having very high selectivity for propylene. When the temperature is at 140–180 °C, ZSM-34-S zeolite could be crystallized for 2–6 h in the presence of ZSM-34 crystals as seeds. For industry, a fast and organotemplate-free synthesis, a typically green route, means significant savings in energy and costs. Characterizations using XRD, SEM, ²⁷Al and ²⁹Si MAS NMR, and N₂ sorption techniques show that the ZSM-34-S crystals grow from the seeds of ZSM-34 crystals in an amorphous aluminosilicate. Catalytic tests of the MTO reaction show that HZSM-34-S has a very high selectivity for propylene (55.2%), which is even higher than that (47.0%) of SAPO-34 under the same conditions. Moreover, the hydrothermal treatment of HZSM-34-S significantly improves the catalyst life for MTO due to decreasing acidic concentration and increasing anti-deactivation. The combination of a “green” synthesis and the good catalytic performance of ZSM-34-S would be potentially important for the highly effective conversion of methanol, which can be easily obtained from coal, natural gas, or biomass at a large scale.