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

Abstract

La doped ZnxAlyOz 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 ZnxAlyOz catalysts.