Steam-treated SAPO-18 with well-regulated acidity and excellent DTO performance

Abstract

The hydrothermally synthesized SAPO-18 catalyst was steam treated to investigate the catalytic performance in dimethyl ether to olefins (DTO) reaction. After steam treatment, micropores and mesopores were created on the SAPO-18 catalyst. To evaluate the catalytic activity of steamed SAPO-18, the DTO reaction was carried out at 673 K with weight hourly space velocity (WHSV) of 3.546 h⁻¹, and the steamed SAPO-18 (S-773) at 773 K exhibited excellent DTO conversion performance (single-run lifetime 5.5 h, light olefin selectivity 95.9 %) with BET surface area of 737 m² g⁻¹, mesopore volume of 125 mm³ g⁻¹, total amount of acid sites of 533 μmol g⁻¹, and Brønsted/Lewis ratio of 0.97. The improvement of DTO stability can be attributed to the increased mesoporosity and significantly reduced total amount of acid sites (well-regulated Brønsted/Lewis ratio) after steam treatment of SAPO-18 catalyst.