Facile preparation of highly thermal conductive ZnAl2O4@Al composites as efficient supports for cobalt-based Fischer-Tropsch synthesis

Abstract

The development of alternative to silicon carbide (SiC) holds great promise in energy and environmental related catalysis because the harsh preparation process and high cost limit its large-scale application. In this work, the core-shell structured ZnAl2O4@Al ceramic-metal composites (Zn-Al-T) are prepared from low cost metallic Al powder by a facile and environment-friendly approach to replace silicon carbide for Co-based Fischer-Tropsch synthesis (FTS, a typical strong exothermic heterogeneous catalytic reaction). The composition, thermal conductivity, surface chemical properties and pore configuration of the ZnAl2O4@Al composites can be easily modulated by controlling the calcination condition. Among Zn-Al-T composites, the Zn-Al-650 and Zn-Al-750 samples demonstrate optimum coupling of physicochemical properties, i.e., robust chemical stability, meso-macropore structure (wide mesopore and high macroporosity) and high thermal conductivity. Thus, the excellent FT performance (low CH4 selectivity and high selectivity to C5+) was obtained on the Co/Zn-Al-650 and Co/Zn-Al-750 catalysts. The heat transfer experiments were conducted on a special tubular fixed-bed reactor (I.D. = 22 mm) under near-industrial conditions. At similar reaction rates, the effective radial thermal conductivity coefficient (keaff) in the Co/Zn-Al-650 catalyst bed is 3–4 times and 1–2 times that in the Co/Al2O3 and Co/SiC catalyst beds respectively, resulting in a more uniform temperature distribution in Co/Zn-Al-650 catalyst bed. In addition, the ZnAl2O4@Al composite has wide application prospect in strong exothermic/endothermic catalytic system owing to its high thermal conductivity, adjustable physico-chemical properties, facile preparation method and low cost.