Abstract: Effects of SiO2/Al2O3, P2O5/Al2O3 and H2O/Al2O3 ratios in the synthesis gel on the crystallization of SAPO-34 were systematically studied with triethylamine as a templating molecule for the purpose of improving its catalytic performance in MTO reaction. Pure SAPO-34 phase can only be synthesized with the synthesis gel having a SiO2/Al2O3 ratio larger than 0.25, demonstrating the structure-directing role of Si. Nevertheless, a further increase in the Si content in the synthesis gel led to not only the formation of Al2O3 but also the decrease in the crystallinity, surface area and catalytic stability of SAPO-34. The P2O5/Al2O3 and H2O/Al2O3 ratios in the synthesis gel also significantly influenced the crystallization and catalytic performance of SAPO-34. When P2O5/Al2O3 and H2O/Al2O3 were 1.1 and 36 respectively, the synthesized sample with a (P+Si)/Al ratio close to 1 showed high surface area and appropriate acidity, resulting in a catalytic lifetime of 520 min without lowering olefin selectivity. The catalytic performance of SAPO-34 is also highly dependent on its calcination conditions. The sample calcined at 550 oC for 8 h in flowing air showed a much higher catalytic stability (its catalytic lifetime reached 580 min) than the sample calcined for 10 h under the same conditions as a result of different hydrocarbon residuals kept in SAPO-34 after calcination.

Key words: SAPO-34, Synthesis, Characterization, Calcinaiton, MTO