Synthesis of light olefins and alkanes on supported iron oxide catalysts

Abstract

Catalytic synthesis of C1–C4 hydrocarbons from clean synthesis gas, representative of natural gas, biomass or coal, was investigated over conventional supported catalyst (FeOx/Al2O3 and FeOx/ZrO2) and compared with catalytic cartridges made from anodized Al plates (FeOx/AAO-Al). Porous aluminum oxide layers (ca. 50 and 100μm thick) and uniform meso/macro pores (ca. 25–50nm, 50–75nm diam.) were established on Al plates by anodization treatment. Iron was supplied by incipient wetness impregnation (particles), wet impregnation and ultrasonic spray deposition (plates). Catalysts were characterized by SEM, XPS, H2-TPR N2-BET and Hg porosimetry. Synthesis performance was studied at 350–500°C, H2/CO ratios 1–3 and atmospheric pressure. Loading of FeOx and its reducibility was favoring gaseous products and determining reaction mode. Conditions were strongly favoring accumulation of carbonaceous material, being governing for performance and limiting lifetime. Low olefins selectivity (< 5%) and yields (< 1%) were obtained. Addition of 1wt.%K favored syngas conversion and deactivation, 1.2wt.% Cu caused no effect. Results indicate that large pores favor olefin selectivity and lifetime. The catalyst working state, as evolving during reaction was independent on initial state (calcined oxide, reduced, precursor nitrate salts), indicating that thermodynamics was structure controlling.