Syngas to light olefin synthesis over La doped ZnxAlyOz composite and SAPO-34 hybrid catalysts

Abstract

La doped Zn_xAl_yO_z catalysts were prepared with various precipitating agents and pH values and used in the direct synthesis of light olefins from syngas by combining with SAPO-34. It is found that the precipitating agents and pH values have significant effects on phase composition, surface acidity/basicity and textural properties, which lead to different catalytic performance. The reaction results show that compared to using (NH₄)₂CO₃, NaOH and Na₂CO₃ as the precipitating agents, the catalyst precipitated with NH₄OH at pH 7 has the best activity. The selectivity to light olefins (C₂–C₄⁼) can reach up to 81.4% with 14.2% CO conversion at 380 °C and 2 MPa. Characterization results show that cubic spinel structured ZnAl₂O₄ is formed and co-exists with amorphous ZnO and Al₂O₃ when precipitated with NH₄OH at pH 7, which has a suitable amount of acidic and basic sites and would contribute to the good catalytic performance. Moreover, in situ DRIFT studies reveal that *HCOO and *OCH₃ species are the key intermediates formed during the hydrogenation of CO to methanol over the La doped Zn_xAl_yO_z catalysts.