Conversion of Y into SSZ-13 zeolites and ethylene-to-propylene reactions over the obtained SSZ-13 zeolites

Y zeolites having wide ranges of SiO₂/Al₂O₃ ratios (silica/alumina ratios or SARs) were converted into SSZ-13 zeolites in the presence of N,N,N-trimethyl-1-adamantanamine iodide (TMAda-I) as a template. SSZ-13s with increased SARs could be obtained from Y zeolites having SARs of 5.1-80 and sodium silicate by both conventional electric (CE) and microwave (MW) heating. The syntheses conducted using MW and CE heating at 140 °C were completed in 2 h and 144 h, respectively, because of accelerations by MW in both the nucleation and crystal growth stages. The obtained yields of SSZ-13 decreased as SARs of the starting Y zeolites increased, demonstrating the relatively easy conversion of aluminous Y into SSZ-13. The obtained SSZ-13s with wide SAR ranges (19-287) were applied as catalysts in the direct conversion of ethylene-to-propylene (ETP) to understand the effect of the SARs on the ETP performances, including the conversion of ethylene and propylene selectivity. The stability of ETP was highly dependent on the SAR of the SSZ-13 zeolites. SSZ-13s with excessively high or low SARs caused low ethylene conversion (from the beginning of the reaction) or rapid deactivation in the conversion, respectively. The propylene selectivity or yield (at a fixed ethylene conversion of 80%) generally increased with decreasing SARs (up to 19) of SSZ-13s under the studied conditions because of a steady increase in the selectivities for butenes and higher products with increasing SARs of SSZ-13s.